High-Temperature Short-Time and Ultra-High-Temperature Processing of Juices, Nectars and Beverages: Influences on Enzyme, Microbial Inactivation and Retention of Bioactive Compounds

Abstract

HTST (high-temperature short-time) pasteurization and UHT (ultra-high-temperature) sterilization are techniques commonly used in the dairy industry. Although the use of these methods in fruit and vegetable processing is also well known, the multitude of diverse food matrices determines the need to test and adjust process parameters in order to obtain the best quality of the final product. HTST and UHT are methods that provide effective inactivation of microorganisms and enzymes. Despite the fact that UHT and HTST are thermal processes that cause degradation of bioactive ingredients or color change, in many cases, these two methods are superior to traditional pasteurization, which uses significantly longer exposures to high temperatures. Therefore, this article aims to review the effect of HTST and UHT processing on the quality of juices, nectars and beverages, taking into consideration the quality characteristics, like the presence of microorganisms, pH, titratable acidity, total soluble solids, turbidity, color parameters, contents of bioactive components, antioxidant activity, enzymatic activity and volatile compounds. The impacts of HTST and UHT methods on various food products are discussed, including the food matrix, preservation parameters and the mechanism of interaction. The ability to modify the processing parameters can allow for the selection of adequate preservation parameters for individual products and better results than other unconventional methods, such as HPP (high-pressure processing) or PEF (pulsed electric field). Based on the cited literature, it can be concluded that pH, titratable acidity and TSS most often experience slight changes. As for the other parameters considered, it is extremely important to choose the right temperature and duration for a specific food matrix.

1. Introduction

Regular consumption of fruits and vegetables has been proven to improve human well-being and reduce incidences of type II diabetes, cancer, obesity and other diet-related diseases [1]. Fruits and vegetables exhibit anti-inflammatory, antihypertensive, and antioxidant properties. This is due to the presence of bioactive components, such as fiber, vitamins, phenolics and carotenoids [2,3]. Because of their short shelf-lives, it is necessary to process them properly and preserve the resulting products with available methods.

The most common method of preserving fruit and vegetable products is pasteurization [4], generally using temperatures of between 80 and 90 °C and a time duration of several minutes. Despite ensuring adequate enzyme inactivation and microbiological stability, it usually leads to negative quality changes [5]. Duhan and Kar [6] indicated that traditional pasteurization of sugarcane juice (70 °C/10 min) resulted in an approximately five-fold reduction in antioxidant activity. Heating at 90 °C for 10 min resulted in a 2–10% decrease in the antioxidant capacity of peach beverage, with negligible changes in total phenolic content and total flavonoid content [7]. Pasteurization (95 °C/3 min) led to reductions in individual anthocyanin contents of unclarified (39–51%) and clarified (11–18%) crude black mulberry juice [8]. Bhagat and Chakraborty [9] indicated absolute color differences in pomegranate juice of ∆E = 4.19 and ∆E = 6.29 after heating at 95 °C for 2 and 3 min, respectively.

Because of changing consumer needs, including the search for products with high contents of bioactive ingredients and highly rated organoleptic quality, recently, intensive studies have been conducted on the use of modern preservation methods [3,10,11,12,13,14,15]. Also, because of numerous negative reports on the effects of heating on the quality of fruit and vegetable products [12,16,17,18,19], further research is needed to optimize preservation parameters in order to obtain the best possible quality. Two modern and still improving methods of food preservation are HTST (high-temperature short-time) pasteurization and UHT (ultra-high-temperature) sterilization. Thanks to the better heat exchange and much shorter exposition time for heating than traditional pasteurization, HTST and UHT allow for obtaining a better quality final product [20].

The aim of the paper is to review the effects of HTST and UHT processing on the quality of juices, nectars and beverages, taking into account quality characteristics such as the presence of microorganisms, pH, titratable acidity, total soluble solids, turbidity, color parameters, content of bioactive components, antioxidant activity, enzymatic activity and volatile compounds. This article can serve as a significant compendium of knowledge for use in work on food processing and scientific research design. Highlighting the different directions of the changes in individual quality characteristics of different food matrices confirms the need for continuous research on the selection of appropriate parameters, also taking into account the food matrix.

When searching for publications, we were guided by the time criterion (40% of all publications used are articles within the last 5 years (i.e., 2020–2024) and 70% from the last 10 years, i.e., 2015–2024) to ensure the timeliness of the review, along with keywords. The use of older publications—prior to 2015—was intended to demonstrate that the discussed methods have been developed over the long term. To ensure the broadest coverage and inclusion of as many relevant publications as possible, we used internationally recognized and reliable scientific databases such as Web of Science and Scopus.

2. Applications of UHT and HTST

UHT and HTST are methods of thermally preserving liquid products in a flow-through tubular or plate pasteurizers. They are most often accompanied by bottling into pre-sterilized containers [21]. In the literature, different ways of distinguishing UHT and HTST from each other are encountered. For example, Zvaigzne et al. [22] stated that the UHT method is heating at temperatures above 135 °C for 1–2 s, while Aguiló-Aguayo et al. [21] stated that UHT requires a higher temperature than HTST, above 100 °C, and a shorter time of up to a few seconds. Based on an analysis of the literature on the topic, it can be concluded that the decisive differentiating factor among the analyzed methods is the process temperature. UHT preservation happens at temperatures above 100 °C and a time limited to 10 s, while HTST processing takes place at temperatures up to 100 °C and from few up to several dozen of seconds.

The following stages can be distinguished in both of the preservation techniques: pre-heating, high heating, cooling, and sterile or aseptic packaging. Before these, food products are often homogenized to increase and unify the heat transfer by volume. HTST/UHT systems can work in the direct mode—whereby the product and heating medium are in direct contact with each other. But the most common choice is the use of devices that work in the indirect mode, where the product and heating medium do not come into contact with each other, and heat is transferred via a heat exchanger [23]. In the food industry, UHT and HTST, as continuous flow thermal processes, are mainly applied to milk, soup, honey, stew, soy milk, wine, yogurt and cream [22]. In fruit and vegetable processing, the UHT and HTST methods are used for juices, nectars and beverages.

The most common UHT preservation parameter found in the literature is 110 °C/8.6 s. In the application of the UHT technique for juice preservation, temperatures in a range of 110–138 °C and durations of 2–8 s are used the most often, following the principle that the higher the temperature, the shorter the time. In the case of the application of the HTST technique for heating juices and beverages, the most common temperature chosen is 90 °C, although trials are most often conducted with a temperature range of 71.1–100 °C and times of 2–90 s. Detailed summaries of the temperatures used, depending on the type of technique, as well the type of juice, nectar or beverage, are included in tables in this manuscript.

3. Advantages and Disadvantages of UHT and HTST

It is emphasized that the UHT and HTST methods have smaller impacts on the sensory and physicochemical qualities of fruit products compared to traditional pasteurization. This is possible because of the use of high temperatures and shorter processing times. Moreover, direct heating of the product prior to packaging increases the efficiency of the process, because the resistance associated with the packaging material is omitted and the direction of the heat flow during this process changes. These techniques also ensure a high degree of preservation by ensuring the commercial sterility and microbiological safety of the product, allowing for a relatively long shelf-life while maintaining the desired sensory characteristics. However, high temperatures still affect the degradation of bioactive ingredients, such as vitamin C and phenolics, as well as aromatic compounds, and, therefore, reduces antioxidant activity, as well as changes in sensory and nutritional characteristics [21,24,25,26,27]. The color changes in HTST and UHT products result not from the activity of enzymes but because high temperatures inactivate them. This is the consequence of nonenzymatic browning reactions (Maillard reaction and caramelization), degradation, or oxidation of pigments due to exposure to heat [27]. It is emphasized that heating at high temperatures may lead to unfavorable changes in aroma, such as an unacceptable off-flavor or odor when cooked [28]. Thermal treatment may also lead to decreases in the quality of proteins and lipid oxidation, as well as depreciation of the biological viabilities of the natural color pigments, influencing consumers’ preferences and loss of product marketability [29]. Compared to nonthermal preservation methods, such as high-pressure processing (HPP), high-pressure homogenization (HPH) or ultrasound (US), HTST and UHT may lead to much greater changes in color due to the thermal degradation of color substances or nonenzymatic browning reactions [30,31]. Also, because of thermally induced reactions in the products, the profiles of the aroma compounds may change, as well as consumer acceptance and assessments of quality characteristics, such as taste, smell and color. Samples preserved under high pressure are better in quality in these aspects [25,32]. Therefore, it is important to appropriately select the processing parameters (i.e., time and temperature) in order to maintain product quality as much as possible and, at the same time, ensure sufficient shelf-lives [24]. Over the years, researchers have tried to optimize the process conditions, including by shortening processing times and minimizing unfavorable losses, but this is not always fully possible [21].

4. Impacts of HTST and UHT on Food Quality

4.1. Microbiological Quality and Shelf-Life

Occurrences of microorganisms in fruit and vegetable products are related to contamination of the raw materials’ surfaces during harvesting and further processing. The heat resistance of microorganisms depends on many factors, such as pH, redox potential, water activity, moisture content, salt content, types of targeted microorganisms and activities of the enzymes [21,33]. For selecting the preservation parameters, the most important factor to take into consideration is the pH. Products with a pH up to 4.5 are preserved with temperatures up to 100 °C (pasteurization), inactivating non-spore-forming bacteria, while products with a pH above 4.5 are preserved with temperatures above 100 °C (sterilization), inactivating non-spore-forming and spore-forming microorganisms [21,23]. To ensure their safety, a 5-log reduction in microorganisms is needed [9]. Heat affects various parts of microbial cells and their functioning, ultimately leading to varying degrees of inactivation. The most relevant cellular events that occur in a vegetative bacterial cell associated with heat treatment are DNA alterations; increases in the mutation rate; denaturation and aggregation of proteins; loss of specific protein function; reduction in protein repair capacity; ribosome confirmation loss; outer- and inner-membrane permeabilizations; loss of membrane-associated functions; and loss of intracellular components [34].

A detailed summary of the effects of the UHT and HTST parameters on the preservation efficiency of juices, nectars and beverages is provided in Table 1. According to the literature, the UHT method is very effective in preserving liquid food products. Xu et al. [25] showed that this method resulted in reducing the numbers of the total aerobic bacteria (TAB) and the yeasts and molds (Y&M) to below detection limits and provided a shelf-life for kiwifruit juice of 42 days at 4 °C. Wang et al. [35] also observed TAB and Y&M contents below the detection limits for 12 weeks in purple sweet potato nectar stored at 4 °C and 25 °C. Huang et al. [36] demonstrated complete inactivation of aerobics, psychrotrophs, Escherichia coli Coliformis and Y&M in carambola juice after the process, as well as within 40 days of storage. Wang et al. [24] compared different UHT temperatures within the same preservation time, showing that better inactivation occurred at 120 °C and 135 °C than at 110 °C. However, both of these temperatures effectively inactivated microorganisms to safe levels. Chen et al. [37] achieved desirable 90-day shelf-life for pomegranate juice after UHT treatment. Also, other studies have shown the effectiveness of the UHT method in inactivating microorganisms immediately after processing [12,17,38,39,40], maintaining microbiological safety during storage over 20 days [40,41], 25 days [42], 28 days [27], 90 days [43] and 16 weeks [44,45]. Compared to innovative, emerging methods of preservation like HPP, UHT is much more effective [41].

The HTST method is also effective in ensuring appropriate microbiological stability. Heating peach juice at 72 °C for 15 s resulted in the destruction of E. coli O157:H7 by 5 logarithmic cycles [31]. Heating sea buckthorn juice at a configuration of 100 °C/15 s reduced TAB and Y&M counts below detection levels and ensured microbiological safety for 31 days at 4 °C [30]. The good effectiveness of the HTST treatment in inactivating various microorganisms has been demonstrated in many other research works [5,40,46,47,48,49]. Deng et al. [5] indicated a shelf-life for cloudy apple juice of 9 weeks. Microbial counts for the HTST-pasteurized orange juice (94 °C/26 s) remained at or below detection limits over the entire study (168 days) [50].

Table 1. Effects of UHT and HTST processing on microbial contents.

Matrix	Parameter	Contents of Microorganisms	Reference
UHT
Mango nectar	110 °C/8.6 s	Total aerobic bacteria counts 5.7 log ↓ * Yeasts and molds—nondetected	[45]
Watermelon juice	135 °C/2 s	Total flora count more than 3.8 log ↓ *	[43]
Watermelon juice	110 °C/2 s, 120 °C/2 s, 135 °C/2 s	Total flora count—survival rate below 0.01%, 0.1% and 0.01%, respectively	[24]
Açai juice	138 °C/6 s	Yeast and mold counts 2.2 log ↓ *	[51]
Carrot juice	110 °C/8.6 s	Total plate count 4.9 log ↓ * Yeasts and molds—nondetected	[52]
Pepper and orange juice blend	110 °C/8.6 s	Total aerobic bacteria—nondetected Yeasts and molds—nondetected	[42]
Cucumber juice	110 °C/8.6 s	Total aerobic bacteria 3.6 log ↓ * Yeasts and molds—nondetected	[41]
Grapefruit juice	110 °C/8.6 s	Total plate count—nondetected Yeasts and molds—nondetected	[53]
Korla pear juice	110 °C/8.6 s	Total plate count—nondetected Yeasts and molds—nondetected	[54]
Carambola juice	110 °C/8.6 s	Total aerobics, psychrotrophs, E. coli/coliforms, yeasts and molds—nondetected	[36]
Mulberry juice	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[27]
Cloudy ginger juice	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[38]
Papaya beverage	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[39]
Clear and cloudy Se-enriched kiwifruit juices	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[25]
Apricot nectar	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[20]
Red prickly pear juice	130 °C/3 s	Total coliforms, yeasts and molds, mesophilic and psychrophilic—nondetected	[40]
Black carrot juice	130 °C/5 s	Total bacterial content, E. coli and yeasts and molds—nondetected	[17]
Freshly squeezed lettuce juice	115 °C/5 s	Total aerobic bacteria, yeasts and molds ↓ * (commercial asepsis)	[12]
Mulberry juice	110 °C/8.6 s	Total viable bacteria and yeasts and molds—below 1 log CFU	[55]
HTST
Sea buckthorn juice	100 °C/15 s	Total aerobic bacteria counts 3.0 log ↓ * Yeast and mold counts—nondetected	[56]
Orange and carrot juice	98 °C/21 s	Total plate counts—nondetected Yeast and mold counts—nondetected	[46]
Nonconcentrated and concentrated sea buckthorn juice	100 °C/15 s	Total plate counts—nondetected Yeast and mold counts—nondetected	[30]
Cloudy apple juice	98 °C/50 s	Total aerobic bacteria counts—nondetected Yeast and mold counts—nondetected E. coli—nondetected	[5]
Açai juice	90 °C/6 s	Yeast and mold counts 1.8 log ↓ *	[51]
Orange juice	72 °C/20 s	E. coli, Enterobacteriaceae, yeasts and molds < 10 cfu/g Total aerobic plate counts < 1000 cfu/g Lactic acid bacteria < 100 cfu/g	[48]
Pomegranate juice (MW—Mollar de Elche varietal juice + Wonderful varietal juice; ML—Mollar de Elche + lemon juice; M100—Molar de Elche)	90 °C/5 s	Total mesophilic aerobic plate count—nondetected	[57]
Red prickly pear juice	80 °C/30 s	Total coliforms, yeasts and molds, mesophilic and psychrophilic—nondetected	[40]
Peach juice	72 °C/15 s	E. coli O157:H7 5-log reduction	[31]
Pomegranate fermented beverage	72 °C/15 s	Aerobic mesophilic bacteria 1.3 log ↓ * Yeasts and molds 3.0 log ↓ *	[58]
Orange juice	94 °C/26 s	Total aerobic bacteria—below detection limit	[50]
Apple juice with raspberry	85 °C/6 s	Total aerobic mesophilic and psychrophilic counts, yeasts and molds—nondetected	[13]
Apple juice	72 °C/26 s	Native microorganisms 5 log ↓	[59]
Fruit smoothie-type beverage	72 °C/15 s	Native microorganisms 3.5 log ↓ * E. coli 6.3 log ↓ *	[60]
Kale juice	72 °C/60 s	Total plate count 5.5 log ↓	[61]
Whey–grape juice drink	72 °C/15 s	Bacterial counts below 1 CFU/mL	[62]

↓—decrease. * Statistically significant change.

Table 1. Effects of UHT and HTST processing on microbial contents.

Matrix	Parameter	Contents of Microorganisms	Reference
UHT
Mango nectar	110 °C/8.6 s	Total aerobic bacteria counts 5.7 log ↓ * Yeasts and molds—nondetected	[45]
Watermelon juice	135 °C/2 s	Total flora count more than 3.8 log ↓ *	[43]
Watermelon juice	110 °C/2 s, 120 °C/2 s, 135 °C/2 s	Total flora count—survival rate below 0.01%, 0.1% and 0.01%, respectively	[24]
Açai juice	138 °C/6 s	Yeast and mold counts 2.2 log ↓ *	[51]
Carrot juice	110 °C/8.6 s	Total plate count 4.9 log ↓ * Yeasts and molds—nondetected	[52]
Pepper and orange juice blend	110 °C/8.6 s	Total aerobic bacteria—nondetected Yeasts and molds—nondetected	[42]
Cucumber juice	110 °C/8.6 s	Total aerobic bacteria 3.6 log ↓ * Yeasts and molds—nondetected	[41]
Grapefruit juice	110 °C/8.6 s	Total plate count—nondetected Yeasts and molds—nondetected	[53]
Korla pear juice	110 °C/8.6 s	Total plate count—nondetected Yeasts and molds—nondetected	[54]
Carambola juice	110 °C/8.6 s	Total aerobics, psychrotrophs, E. coli/coliforms, yeasts and molds—nondetected	[36]
Mulberry juice	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[27]
Cloudy ginger juice	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[38]
Papaya beverage	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[39]
Clear and cloudy Se-enriched kiwifruit juices	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[25]
Apricot nectar	110 °C/8.6 s	Total aerobic bacteria, yeasts and molds—nondetected	[20]
Red prickly pear juice	130 °C/3 s	Total coliforms, yeasts and molds, mesophilic and psychrophilic—nondetected	[40]
Black carrot juice	130 °C/5 s	Total bacterial content, E. coli and yeasts and molds—nondetected	[17]
Freshly squeezed lettuce juice	115 °C/5 s	Total aerobic bacteria, yeasts and molds ↓ * (commercial asepsis)	[12]
Mulberry juice	110 °C/8.6 s	Total viable bacteria and yeasts and molds—below 1 log CFU	[55]
HTST
Sea buckthorn juice	100 °C/15 s	Total aerobic bacteria counts 3.0 log ↓ * Yeast and mold counts—nondetected	[56]
Orange and carrot juice	98 °C/21 s	Total plate counts—nondetected Yeast and mold counts—nondetected	[46]
Nonconcentrated and concentrated sea buckthorn juice	100 °C/15 s	Total plate counts—nondetected Yeast and mold counts—nondetected	[30]
Cloudy apple juice	98 °C/50 s	Total aerobic bacteria counts—nondetected Yeast and mold counts—nondetected E. coli—nondetected	[5]
Açai juice	90 °C/6 s	Yeast and mold counts 1.8 log ↓ *	[51]
Orange juice	72 °C/20 s	E. coli, Enterobacteriaceae, yeasts and molds < 10 cfu/g Total aerobic plate counts < 1000 cfu/g Lactic acid bacteria < 100 cfu/g	[48]
Pomegranate juice (MW—Mollar de Elche varietal juice + Wonderful varietal juice; ML—Mollar de Elche + lemon juice; M100—Molar de Elche)	90 °C/5 s	Total mesophilic aerobic plate count—nondetected	[57]
Red prickly pear juice	80 °C/30 s	Total coliforms, yeasts and molds, mesophilic and psychrophilic—nondetected	[40]
Peach juice	72 °C/15 s	E. coli O157:H7 5-log reduction	[31]
Pomegranate fermented beverage	72 °C/15 s	Aerobic mesophilic bacteria 1.3 log ↓ * Yeasts and molds 3.0 log ↓ *	[58]
Orange juice	94 °C/26 s	Total aerobic bacteria—below detection limit	[50]
Apple juice with raspberry	85 °C/6 s	Total aerobic mesophilic and psychrophilic counts, yeasts and molds—nondetected	[13]
Apple juice	72 °C/26 s	Native microorganisms 5 log ↓	[59]
Fruit smoothie-type beverage	72 °C/15 s	Native microorganisms 3.5 log ↓ * E. coli 6.3 log ↓ *	[60]
Kale juice	72 °C/60 s	Total plate count 5.5 log ↓	[61]
Whey–grape juice drink	72 °C/15 s	Bacterial counts below 1 CFU/mL	[62]

↓—decrease. * Statistically significant change.

4.2. Basic Physicochemical Characteristics

Total soluble solids (TSS) is one parameter that determines the organoleptic characteristics of juices, nectars and beverages. It indicates the content of water-soluble and nonvolatile substances in the studied food matrix. Changes in TSS are associated mainly with changes in the compounds such as sugars and organic acids. A second important parameter influencing the organoleptic characteristics of food is titratable acidity (TA), which corresponds to the total concentration of acidic hydrogen ions. pH is the main indicator for the selection of preservation parameters and determines the microbiological stability of the product. Turbidity and color are the primary qualitative discriminators that a consumer is able to assess during contact with food. The content of macromolecular compounds, as well as chemical reactions, especially thermally induced ones, can lead to an increase or decrease in the turbidity of liquid products.

4.2.1. Total Soluble Solids

The UHT technique, because of the very fast processing time, does not significantly affect the components of the TSS. Generally, many studies confirm the lack of significant changes in TSS after preservation with this method [22,35,36,37,39,41,45,52,53,54], as well as during storage [27,41,42,45,53]. However, different observations are found by Jittanit et al. [63]. The significant decrease in TSS they noted was caused by the design of the equipment. The authors assume that because of the need to constantly supply water to the apparatus, the test sample could be diluted and the TSS decreased. Decreases in TSS were also demonstrated by other studies [12,17,42]. Moreover, no significant effects of UHT on the contents of sucrose, glucose and fructose in purple sweet potato nectar were revealed [35]. In another study, there was no effect on the sucrose content, but significant decreases in glucose, fructose and total sugars were observed [45].

Thermal processing of peach juice (72 °C/15 s) did not result in a significant change in TSS following HTST treatment compared to raw juice immediately after processing, as well as during 28 days of storage [31]. Also, other studies have shown no significant effects of HTST on the TSS of juices, nectars and beverages from fruits and vegetables immediately after preservation [5,22,30,32,50,64,65], as well as during storage [5,50,65,66]. Bonilla et al. [67], examining three blackberry–soy–flaxseed-based beverages, also confirmed the lack of significant effects of HTST preservation (71.1 °C/3 s) on TSS. Rivas et al. [46] indicated a 9.5% increase in the TSS in blended orange and carrot juice. In lime juice, a decrease of more than 8% in TSS (85 °C/30 s and 95 °C/30 s) was observed [63].

4.2.2. pH

Many researchers have found no significant changes in pH after UHT [35,38,40,41,53], as well as during storage [27,35,39,40,41,53]. Only a few researchers found a drop in the pH after the preservation process [17,54,63] or during storage [45].

Typically, researchers indicate that there is no significant effect of HTST heating on pH immediately after preservation [5,13,30,32,40,46,48,50,64,65,66,67] and during storage [48,50,65]. However, some researchers point to an increase or decrease in pH after preservation. When preservation conditions of 73 °C/27 s, 80 °C/27 s or 83 °C/27 s were applied to an apple juice, the pH increased by more than 6% [68]. Heating lime juice at 85 °C for 30 s and 95 °C for 30 s resulted in a significant decrease in pH [63]. Conditions of 72 °C/15 s resulted in a significant reduction of 3% in peach juice pH, while the pH dropped by 9.4% over 28 days of storage. However, the dynamics of the changes in pH were less than those in fresh juice, for which the pH decreased by 16.4% [31]. A decrease in pH after the process was also observed by other researchers [69]. There was a decrease in pH of 38.6% during a 50-day storage period, as stated by Zhao et al. [66]. Deng et al. [5] indicated that there was no effect of HTST heating on pH over 9 weeks of storage.

4.2.3. Titratable Acidity

Researchers have mostly determined that there is no significant change in titratable acidity (TA) after UHT preservation [22,25,36,38,41,45,53], as well as during storage [25,35,53,54]. Chen et al. [38], despite showing no significant change in the TA of cloudy ginger juice immediately after preservation, indicated a significant decrease in TA during a 91-day storage period. However, different reports can be found in the literature. Chen et al. [37], in pomegranate juice, observed a significant decrease in TA after UHT preservation. Tian et al. [32] observed an increase in TA of almost 7%, using the same parameters as Chen et al. [37]—110 °C/8.6 s. Bao et al. [17] observed a significant 12.9% increase in acidity after UHT preservation of black carrot juice compared to fresh. Liu et al. [45] observed an increase in acidity within 16 weeks of preservation and Liu et al. [41] within 20 days.

The HTST treatment of peach juice (72 °C/15 s) did not result in a significant change in TA compared to raw juice, immediately after preservation, as well as during a 28-day storage period [31]. Other researchers [5,32,49,56] also observed no significant effects of HTST treatment on the acidity of fruit and vegetable products. In contrast, the acidity of orange juice decreased significantly by 7.6% and 8.4% as a result of heating at 90 °C for 10 and 20 s, while an increase in TA was noted over 180 days. A different observation was made by Rivas et al. [46], whereby TA increased by 10.2% in blended juice after the process.

4.2.4. Turbidity

Tian et al. [32] demonstrated a 110.4% increase in turbidity following heating at 110 °C for 8.6 s. On the other hand, Liu et al. [41] and Zhao et al. [54] showed significant decreases in clarity following UHT preservation of 2.2% and 3.7%, respectively. This was likely due to the degradation of various compounds, such as proteins, phenols or polysaccharide. In addition, liquid products preserved thermally by this method are less transparent than after HPP.

HTST treatment (72 °C/15 s), immediately after the process, did not result in a significant change in the turbidity of peach juice, while there was a significant 25.9% reduction in particle size. During storage, there was a significant increase in turbidity but to a lesser extent than in fresh juice [31]. Bonilla et al. [67] observed an increase in turbidity of 6.4–15.5% in three different formulations of blackberry–soy–flaxseed-based beverages. On the other hand, Tian et al. [32] noted a significant increase in turbidity in cloudy pomegranate juice by 79.4% (110 °C/8.6 s). Rivas et al. [46] observed an increase of as much as 105.7% in blended orange and carrot juice.

4.2.5. Color

Color is affected by the presence of color substances, such as anthocyanins (from red to purple or blue in color), chlorophylls (different intensities of green hues), carotenoids (from yellow to orange or red in color) and betalains (betacyanins—red to violet in color; betaxanthins—yellow to orange in color) [29]. The direction of the change depends on the chemical composition of the food and the preservation conditions. During preservation and storage, the presence of oxygen in the container, enzyme activity or chemical transformations of pigments (for example, degradation, polymerization and Maillard reactions) are also important [39,63]. An increase in the preservation temperature, at the same time, results in a greater color change [24]. Tian et al. [32] showed a significant increase in L*, a* and b* and ΔE = 6.6 compared to raw juice using 110 °C/8.6 s parameters for UHT. Xu et al. [25] showed the difference between clear and cloudy juices—in the case of the former, the L*, a* and b* parameters increased significantly after thermal preservation (ΔE = 2.3), while in the latter juice, the L* and b* parameters decreased (ΔE = 4.6). In addition, their colors continued to change significantly during storage. Visible color changes (ΔE > 3) were also demonstrated by other studies [12,36,38,42,49,53]. An intense color change was demonstrated by Jittanit et al. [63] where ΔE = 11.4 was obtained after preservation of lime juice (136°/4 s), and was associated with decreases in L* of 12.5% and a* of 59.7% and an increase in b* of 85.4%. Smaller color changes were indicated by Liu et al. [41] (ΔE = 3.0), Wang et al. [35] (ΔE = 3.0), Chen et al. [37] (ΔE = 2.4), Chen et al. [39] (ΔE = 1.2) and Zou et al. [27] (ΔE = 0.1), but they confirmed the discoloration process during storage. Wang et al. [35] observed that ΔE = 8.0 at 12 weeks of storage at 4 °C and ΔE = 5.4 at 25 °C, while Liu et al. [41] ΔE = 24.0 at 20 days of storage at 4 °C. In contrast, Gao et al. [53] noted no obvious color changes after the process (ΔE = 2.0) or during a 21-day storage period (ΔE between 1.8 and 2.5). Small ΔEs may be due to the inactivation of enzymes. However, it is emphasized that UHT leads to much larger color changes compared to HPP [37,41]. Yuan et al. [70] compared HTST (85 °C/30 s) with UHT (110 °C/8.6 s). Cloudy pomegranate juice preserved at a higher temperature and for a shorter time achieved a higher value of ΔE = 6.8 than that at a lower temperature and for a longer time, at ΔE= 5.5.

Heating peach juice at 72 °C for 15 s resulted in slight decreases in the L* and a* parameters and a significant increase in the b* value immediately after HTST preservation compared to raw juice. There was a significant change in the brightness and proportion of the yellow color during 28 days of storage. After HTST, the peach juice became more yellow and darker [31]. In contrast, heating at 80 °C for 30 s resulted in increases in the L*, a* and b* values of cloudy pomegranate juice [32]. de Souza et al. [64], on the basis of the thermal processing of two juices and a lemonade, showed different effects for the same HTST preservation conditions on the color parameters. In lemonade, there were significant increases in a* and b* values of 5.6% and 3.9%, respectively. In citrus juice, there was an increase in the a* value of 60.0%, and in green juice there were changes in all three color parameters (L* of 14.1%, a* of 120.0% and b* of 4.9%). The consecutive ΔEs for these products were 0.3, 1.4 and 8.0, respectively. In other studies, for cloudy pomegranate juice, the ΔEs were 5.2 under conditions of 80 °C/30 s [32], 3.6 for sea blackthorn juice preserved at 100 °C/15 s [56] and 1.7–2.6 for blackberry–soy–flaxseed beverages preserved at 71.1 °C/3 s [67]. Small changes in the color of the product (ΔE = 0.6) after HTST processing were observed by Rios-Corripio et al. [58]. Yuan et al. [70] compared the effects of HTST (85 °C/30 s) and UHT (110 °C/8.6 s) on the color of cloudy pomegranate juice—the ∆Es were 5.5 and 6.8, respectively. As can be seen, depending on the heating conditions and food matrix, different visual changes in food can occur. Researchers emphasize that the HTST method exhibits worse retention of the natural color of a product than ultrasound, UV-C radiation, high-pressure homogenization or HPP technique [13,30,31]. However, various observations were made by Lee et al. [71]. In three juices from different apple varieties, the authors indicated that the HTST-treated samples experienced much smaller color changes than the PEF-treated samples. They confirmed significant changes in color during storage. The ΔE of cucumber juice drink after 50 days of storage at 4 °C was as high as 9.2 [66].

4.3. Bioactive Compounds

Detailed summaries of the effects of the applied UHT and HTST preservation temperatures on phenolic compounds, vitamins and other bioactive components in fruit and vegetable juices, nectars and beverages are provided in Table 2 and Table 3.

4.3.1. Vitamin C

Vitamin C is a thermolabile, water-soluble antioxidant. It can scavenge singlet oxygen, superoxide radical, hydroxyl radical and hydrogen peroxide [19]. The kinetics of its decomposition depends on numerous factors, such as temperature, pH, light access and the presence of oxygen, metal catalysts or enzymes[71]. Vitamin C contents in products decrease during storage [72]. Degradation is most often associated with the effects of available oxygen (the increase in temperature determines the mobility of the molecules, thus increasing the contact of ascorbic acid with oxygen), causing oxidation of ascorbic acid to dehydroascorbic acid and further degradation to 2,3-diketogulonic acid or the formation of furfural and 3-hydroxy-2-pyrone. Conversion to dehydroascorbic acid is conducted without losses in vitamin C activity, but further degradation results in a loss of these desirable properties [73]. Vitamin C may be partially protected from degradation by the presence of phenolics [74]. Ascorbic acid degradation can reduce the nutritional and sensory quality of food products and cause changes in color and flavor due to nonenzymatic browning reactions [19]. Vitamin C has numerous health-promoting properties and is used in the prevention of numerous diseases, such as heart disease, cancer, the common cold, diabetes, atherosclerosis, macular degeneration, strokes, cataracts, glaucoma and COVID-19 [75]. In addition, it is involved in collagen synthesis and improves iron absorption [72].

UHT heating reduced the vitamin C content by 27.9% in red grapefruit juice [53], 13.4% in korla pear juice [54], and by 38.4% and 22.1% in clear and cloudy kiwifruit juices enriched with selenium, respectively [25] (Table 2). Much greater changes were observed by Zhang et al. [12] in UHT-processed lettuce juice—the vitamin C content dropped by 85.1%. Other researchers have also pointed out the degrading effect of the UHT method in this aspect [18,22,70]. On the other hand, Liu et al. [44] indicated that UHT had no effect on L-ascorbic acid in mango nectar immediately after preservation but showed a significant decreases during 16 weeks of storage at 4 °C and 25 °C, respectively. Huang et al. [36] also showed no significant changes in vitamin C content after preservation. On the other hand, researchers have indicated that by heating at 136 °C for 4.1 s, vitamin C can be extracted and significantly increase in content in acerola juice [76,77]. Researchers highlight that the use of a closed system, which is tubular heat exchange, allows for the protection of this bioactive compound from the degrading effects of oxygen [76].

HTST conditions like 72 °C/15 s resulted in a significant reduction in the ascorbic acid content of peach juice immediately after preservation of 22%. During 28 days of storage, ascorbic acid decreased by 54.3% in HTST-treated juice, while in raw juice, this decrease was only 16.7% [31]. Increased temperatures significantly contribute to changes in the content of bioactive components [31,65]. Amaro et al. [14], in modelling studies on orange juice, indicate that as the HTST preservation temperature increases while maintaining the same processing time, the vitamin C content decreases. Vitamin C retention in orange juice processed at 70, 80, 90 and 100 °C over 10 s were 0.92, 0.87, 0.85 and 0.82, respectively. Other researchers also report decreases in vitamin C contents after HTST preservation, as follows: Mena et al. [57] of 12.9–59.6%, depending on the juice’s composition; Deng et al. [5] of 27.2%; Hou et al. [56] of 14.3%; Yuan et al. [70] of 19.8%; and Zvaigzne et al. [22] of about 9%. In lemonade, the ascorbic acid content decreased by 91.7%, while in citrus juice it only decreased by 12.1% under the same preservation conditions [64]. Atuonwu et al. [78] revealed that there was no significant change in vitamin C content as a result of heating orange juice at 76.8 °C/15 s. Torregosa et al. [65] showed the remaining concentration of ascorbic acid to be at a level of 83%, wherein the use of a pulsed electric field preserved as much as 90% of this vitamin. Yuan et al. [70] suggest that HTST is less effective at preserving vitamin C than high-pressure processing. Torregosa et al. [65] and Deng et al. [5] confirmed that the vitamin C contents of HTST-preserved products decreased significantly during storage. The opposite observation was made by Alves Filho et al. [76] and Fonteles et al. [77], with vitamin C contents increased by 35% in acerola juice after preservation at 90 °C for 120 s. The lack of significant changes due to HTST heating is evidenced by Yildiz and Aadil [26] and Yang et al. [30].

4.3.2. Phenolics

Phenolic compounds are secondary metabolites of plants that are natural antioxidants. In their structure, they have at least one aromatic ring with one or more -OH groups. Phenolics can be divided into flavonoids (anthocyanins, flavanols, flavanones, flavonols, flavones, isoflavones and chalcones) and nonflavonoid molecules (phenolic acids, stilbenes, lignans, tannins and curcuminoids). They are most often combined with other molecules, such as sugars or organic acids, making glycosides [45]. Phenolics have health-promoting properties, such as antioxidant, anti-diabetic, antihypertensive, anti-inflammatory, anti-allergenic, antiatherogenic, antimicrobial, antithrombic, cardioprotective, vasodilatory, neuroprotective, anti-platelet-aggregation, gene-encoding antioxidant enzyme-stimulating, epigenetic regulation and cytotoxic [45,79,80]. Phenolics are reactive and thermally sensitive [81]. The literature reports that quantitative and qualitative changes in phenolics of food matrices are associated with numerous processes, such as plant cell disruption, degradation, hydroxylation, isomerization, oxidative polymerization, methylation, isoprenylation, glycosylation and dimerization. This can lead to changes in biological activity, destruction, modification or formation of new phenolic compounds [35,82,83,84]. Zhang et al. [84], in their study, pointed out the following four possible reasons for the increase in the contents of selected phenolic groups following heating at 110 °C for 8.6 s of red raspberry juice: (1) release of phenols due to partial hydrolysis; (2) release of phenolic compounds from cells that ruptured because of heating; (3) thermal inactivation of oxidases; and (4) change in the numbers and positions of hydroxyl groups in phenolics due to thermal treatment. Confirmations of the presented possible transformations of phenolic compounds are provided in tables in this manuscript, where it can be seen that with the same preservation parameters, the degree of change in the content of individual phenolic compounds can vary significantly.

One of the most important groups of phenolic compounds are anthocyanins. They are glycosides or acylglycosides of anthocyanidins (or aglycones). They have a C6-C3-C6 skeleton. The main anthocyanins in food are cyanidin, delphinidin, pelargonidin, petunidin, peonidin and malvidin. Their color and stability depend on the pH of the environment, ranging from red (methylation, the most stable), through blue (hydroxylation, the least stable) to colorless [85]. During pasteurization, significant degradation usually occurs, resulting in changes in their colors and nutritional values (Table 2). Their stability and degradation depend on the preservation parameters used (temperature, time, heat dose, presence of oxygen and light) and on the properties of the heated product (pH, presence of enzymes, copigments, proteins, sugars and metal ions, chemical structures and concentrations of anthocyanin compounds). Copigmentation also plays a significant role in stabilizing anthocyanins [81,85]. The literature reports that anthocyanin retention can be positively affected by a mild heating step (~50 °C) [85].

Table 2. Effect of UHT processing on the contents of selected bioactive compounds.

Matrix	Parameters	Phenolic Compounds	Vitamins	Other Bioactive Ingredients	Reference
Acerola juice, acerola juice + inulin, acerola juice + gluco-oligosaccharides	136 °C/4.1 s	-	All—vitamin C ↑ *	-	[76]
Mango nectar	110 °C/8.6 s	TPC—no statistical difference	Vitamin C—no statistical difference	TCC—no statistical difference	[44]
Watermelon juice	110 °C/2 s 120 °C/2 s 135 °C/2 s	TPC ↓ * at 110 and no statistical difference at 120 and 135 °C	-	-	[24]
Pomegranate juice	110 °C/8.6 s	Total monomeric anthocyanins 29.3% ↓	Vitamin C 40.8% ↓ *	-	[70]
Orange juice	130 °C/2 s	TPC—7.2% ↓	Vitamin C 7.2% ↓ *	TCC 13.7% ↓ *	[22]
Açai juice	138 °C/6 s	TPC ↓ * Anthocyanins ↓ *	Vitamin C ↓ *		[51]
Carrot juice	110 °C/8.6 s	TPC 11.5% ↓ *	-	Lutein 5.1% ↓ α-Carotene 6.2% ↓ * β-Carotene 43.0% ↓ * Falcarindiol 29.7% ↑ * Falcarindiol-3-acetate 37.4% ↑ * Falcarinol 29.1% ↑ *	[52]
Pepper and orange juice	110 °C/8.6 s	TPC—no statistical difference	Vitamin C ↓ *		[42]
Tomato juice	110 °C/8.6 s	Quercetin ↓ * Caffeic acid ↓ Chlorogenic acid—no statistical difference	Vitamin C ↓ *	TCC 7.3% ↓, total lycopene 8.1% ↓, 15-cis-phytoene 5.3% ↓, all-trans -phytoene 5.5% ↓, all-trans-lutein 5.6% ↓, 13-cis-lutein 12.8% ↓ *, 13-cis-β-carotene 8.0%↓, 15-cis-β-carotene from 0 to 0.208 μg/g, all-trans-β-carotene 17.8% ↓ *, cis-β-carotene 7.9% ↓, 9-cis-β-carotene 12.3% ↓, 15-cis-lycopene 57.6% ↑ *, 13-cis-lycopene from 0 to 0.432 μg/g, 9,13-cis,cis-lycopene 9.3% ↓, 9-cis-lycopene 22.0% ↓ *, all-trans-lycopene 9.2% ↓	[18]
Red grapefruit juice	110 °C/8.6 s	TPC 7.7% ↓ *	Ascorbic acid 27.9% ↓ *	-	[53]
Korla pear juice	110 °C/8.6 s	TPC 4.7% ↓ *	Ascorbic acid 13.4% ↓ *	-	[54]
Carambola juice	110 °C/8.6 s	TPC ↓ * Total flavonols—no statistical difference	Ascorbic acid ↓	-	[36]
Mulberry juice	110 °C/8.6 s	TPC 4.0% ↑ *	-	-	[27]
Cloudy ginger juice	110 °C/8.6 s	TPC 14.7% ↓ *	-	Gingerols 14.2% ↓ *	[38]
Papaya beverage	110 °C/8.6 s	TPC 12.7% ↓ *	-	TCC 1.2% ↓	[39]
Litchi juice	134 °C/4 s	TPC 19.8% ↓ * TFC 40.1% ↓ * Rutin 19.3% ↓ *, (−)-epicatechin 36.5% ↓ *, chlorogenic acid 18.7% ↓ *	-	-	[86]
Cloudy pomegranate juice	110 °C/8.6 s	TPC 7.5% ↓ * Anthocyanins 13.2% ↓ *	-	-	[37]
Clear and cloudy Se-enriched kiwifruit juices	110 °C/8.6 s	TPC 5.2% ↑ * and 2.5% ↓	Ascorbic acid 38.4% ↓ * and 26.6% ↓ *	Total selenium 4.9% ↓ * and 27.3% ↓ * Chlorophyll 80.9% ↓ * and 48.5% ↓ *	[25]
Apricot nectar	110 °C/8.6 s	TPC 96.9% ↑ * (+)-catechin 4.7% ↑ *, chlorogenic acid 12.2% ↑ *, neochlorogenic acid 14.6% ↑ *, (−)-epicatechin 5.0% ↓, ferulic acid 5.7% ↑, caffeic acid 12.0% ↑ *, p-coumaric acid 14.3% ↓ *	-	TCC 1.5% ↓, β-carotene 2.6% ↑, α-carotene 44.2% ↑ *, β-cryptoxanthin 13.5% ↓, zeaxanthin 2.8% ↑, lutein 2.7% ↑	[20]
Red prickly pear juice	130 °C/3 s	TPC 2.5% ↑	-	Betacyanins 63.1% ↓ * Betaxanthins 45.0% ↓ *	[40]
Red raspberry juice	110 °C/8.6 s	TPC 31.4% ↓ * TFC 25.5% ↑ Total proanthocyanidins content 5.6% ↑ Total monomer anthocyanins content ↓*	-	-	[84]
Black carrot juice	130 °C/5 s	TFC 14.2% ↓ * Total anthocyanins content 8.6% ↓ * TPC ↓ *	-	TCC ↓	[17]
Cloudy pomegranate juice	110 °C/8.6 s	Total monomeric anthocyanins content 29.3% ↓ * Cyanidin-3-O-glucoside ↓ * Cyanidin-3,5-O-diglucoside ↓ * Delphinidin-3-O-glucoside ↓ * Delphinidin-3,5-O-diglucoside ↓ * Afzelechin-delphinidin-3-O-hexosid ↓ Pelargonidin-3-O-glucoside ↓ * Pelargonidin-3,5-O-diglucoside ↓ *	Vitamin C 40.8% ↓ *	-	[70]
Freshly squeezed lettuce juice	115 °C/5 s	-	Vitamin C 85.1% ↓ * Vitamin E 13.3% ↓ * Vitamin K1 44.2% ↓ * Vitamin B1 25% ↓ Vitamin B2 4.7% ↑ Vitamin B3 2.2% ↓ Vitamin B6 29.7% ↓ * Vitamin B9 31.7% ↓ * Vitamin B12 12.3% ↓ *	Total chlorophyll 14.1% ↓ * Chlorophyll a 13.7% ↓ * Chlorophyll b 14.9% ↓ * Total β-carotene 35.7% ↓ * (all E)-β-carotene 44.2% ↓ * (9Z)-β-carotene 182.7% ↑ *	[12]
Mulberry juice	110 °C/8.6 s	Total anthocyanin content 3.6% ↓ *	-	-	[55]

↑—Increase; ↓—decrease. * Statistically significant change. TPC—total phenolic content; TFC—total flavonoid content; TCC—total carotenoid content.

Table 2. Effect of UHT processing on the contents of selected bioactive compounds.

Matrix	Parameters	Phenolic Compounds	Vitamins	Other Bioactive Ingredients	Reference
Acerola juice, acerola juice + inulin, acerola juice + gluco-oligosaccharides	136 °C/4.1 s	-	All—vitamin C ↑ *	-	[76]
Mango nectar	110 °C/8.6 s	TPC—no statistical difference	Vitamin C—no statistical difference	TCC—no statistical difference	[44]
Watermelon juice	110 °C/2 s 120 °C/2 s 135 °C/2 s	TPC ↓ * at 110 and no statistical difference at 120 and 135 °C	-	-	[24]
Pomegranate juice	110 °C/8.6 s	Total monomeric anthocyanins 29.3% ↓	Vitamin C 40.8% ↓ *	-	[70]
Orange juice	130 °C/2 s	TPC—7.2% ↓	Vitamin C 7.2% ↓ *	TCC 13.7% ↓ *	[22]
Açai juice	138 °C/6 s	TPC ↓ * Anthocyanins ↓ *	Vitamin C ↓ *		[51]
Carrot juice	110 °C/8.6 s	TPC 11.5% ↓ *	-	Lutein 5.1% ↓ α-Carotene 6.2% ↓ * β-Carotene 43.0% ↓ * Falcarindiol 29.7% ↑ * Falcarindiol-3-acetate 37.4% ↑ * Falcarinol 29.1% ↑ *	[52]
Pepper and orange juice	110 °C/8.6 s	TPC—no statistical difference	Vitamin C ↓ *		[42]
Tomato juice	110 °C/8.6 s	Quercetin ↓ * Caffeic acid ↓ Chlorogenic acid—no statistical difference	Vitamin C ↓ *	TCC 7.3% ↓, total lycopene 8.1% ↓, 15-cis-phytoene 5.3% ↓, all-trans -phytoene 5.5% ↓, all-trans-lutein 5.6% ↓, 13-cis-lutein 12.8% ↓ *, 13-cis-β-carotene 8.0%↓, 15-cis-β-carotene from 0 to 0.208 μg/g, all-trans-β-carotene 17.8% ↓ *, cis-β-carotene 7.9% ↓, 9-cis-β-carotene 12.3% ↓, 15-cis-lycopene 57.6% ↑ *, 13-cis-lycopene from 0 to 0.432 μg/g, 9,13-cis,cis-lycopene 9.3% ↓, 9-cis-lycopene 22.0% ↓ *, all-trans-lycopene 9.2% ↓	[18]
Red grapefruit juice	110 °C/8.6 s	TPC 7.7% ↓ *	Ascorbic acid 27.9% ↓ *	-	[53]
Korla pear juice	110 °C/8.6 s	TPC 4.7% ↓ *	Ascorbic acid 13.4% ↓ *	-	[54]
Carambola juice	110 °C/8.6 s	TPC ↓ * Total flavonols—no statistical difference	Ascorbic acid ↓	-	[36]
Mulberry juice	110 °C/8.6 s	TPC 4.0% ↑ *	-	-	[27]
Cloudy ginger juice	110 °C/8.6 s	TPC 14.7% ↓ *	-	Gingerols 14.2% ↓ *	[38]
Papaya beverage	110 °C/8.6 s	TPC 12.7% ↓ *	-	TCC 1.2% ↓	[39]
Litchi juice	134 °C/4 s	TPC 19.8% ↓ * TFC 40.1% ↓ * Rutin 19.3% ↓ *, (−)-epicatechin 36.5% ↓ *, chlorogenic acid 18.7% ↓ *	-	-	[86]
Cloudy pomegranate juice	110 °C/8.6 s	TPC 7.5% ↓ * Anthocyanins 13.2% ↓ *	-	-	[37]
Clear and cloudy Se-enriched kiwifruit juices	110 °C/8.6 s	TPC 5.2% ↑ * and 2.5% ↓	Ascorbic acid 38.4% ↓ * and 26.6% ↓ *	Total selenium 4.9% ↓ * and 27.3% ↓ * Chlorophyll 80.9% ↓ * and 48.5% ↓ *	[25]
Apricot nectar	110 °C/8.6 s	TPC 96.9% ↑ * (+)-catechin 4.7% ↑ *, chlorogenic acid 12.2% ↑ *, neochlorogenic acid 14.6% ↑ *, (−)-epicatechin 5.0% ↓, ferulic acid 5.7% ↑, caffeic acid 12.0% ↑ *, p-coumaric acid 14.3% ↓ *	-	TCC 1.5% ↓, β-carotene 2.6% ↑, α-carotene 44.2% ↑ *, β-cryptoxanthin 13.5% ↓, zeaxanthin 2.8% ↑, lutein 2.7% ↑	[20]
Red prickly pear juice	130 °C/3 s	TPC 2.5% ↑	-	Betacyanins 63.1% ↓ * Betaxanthins 45.0% ↓ *	[40]
Red raspberry juice	110 °C/8.6 s	TPC 31.4% ↓ * TFC 25.5% ↑ Total proanthocyanidins content 5.6% ↑ Total monomer anthocyanins content ↓*	-	-	[84]
Black carrot juice	130 °C/5 s	TFC 14.2% ↓ * Total anthocyanins content 8.6% ↓ * TPC ↓ *	-	TCC ↓	[17]
Cloudy pomegranate juice	110 °C/8.6 s	Total monomeric anthocyanins content 29.3% ↓ * Cyanidin-3-O-glucoside ↓ * Cyanidin-3,5-O-diglucoside ↓ * Delphinidin-3-O-glucoside ↓ * Delphinidin-3,5-O-diglucoside ↓ * Afzelechin-delphinidin-3-O-hexosid ↓ Pelargonidin-3-O-glucoside ↓ * Pelargonidin-3,5-O-diglucoside ↓ *	Vitamin C 40.8% ↓ *	-	[70]
Freshly squeezed lettuce juice	115 °C/5 s	-	Vitamin C 85.1% ↓ * Vitamin E 13.3% ↓ * Vitamin K1 44.2% ↓ * Vitamin B1 25% ↓ Vitamin B2 4.7% ↑ Vitamin B3 2.2% ↓ Vitamin B6 29.7% ↓ * Vitamin B9 31.7% ↓ * Vitamin B12 12.3% ↓ *	Total chlorophyll 14.1% ↓ * Chlorophyll a 13.7% ↓ * Chlorophyll b 14.9% ↓ * Total β-carotene 35.7% ↓ * (all E)-β-carotene 44.2% ↓ * (9Z)-β-carotene 182.7% ↑ *	[12]
Mulberry juice	110 °C/8.6 s	Total anthocyanin content 3.6% ↓ *	-	-	[55]

↑—Increase; ↓—decrease. * Statistically significant change. TPC—total phenolic content; TFC—total flavonoid content; TCC—total carotenoid content.

As a result of the UHT preservation, a significant decrease of 31.4% in the total phenolic content (TPC) of red raspberry juice was observed by Zhang et al. [84]. Chmiel et al. [87] reported a reduction in the TPC of 10–28% in cloudy apple juices, Chen et al. [38] in cloudy ginger juice of 14.7%, Chen et al. [39] in papaya beverage of 12.7%, Gao et al. [53] in red grapefruit juice of 7.7%, and Zhao et al. [54] in korla pear juice of 4.7%. However insignificant changes were noted by Huang et al. [36] in carambola juice. Bao et al. [17], because of UHT preservation of black carrot juice, observed significant decreases in total flavonoid and total anthocyanins contents of 14.2% and 8.6%, respectively. On the other hand, after UHT processing, Zhang et al. [12] observed increases in flavonoid and proanthocyanidins contents of 25.5% and 5.6%, respectively. Increases in TPC contents were noted by Wang et al. [35] and Zou et al. [27] after UHT in purple sweet potato nectar and mulberry juice. No significant changes in TPC were observed by Xu et al. [42] in a pepper and orange juice blend and by Liu et al. [44] in mango nectars. The type of food matrix is of great importance. Xu et al. [25] showed that the effect of beverage clarity is relevant. These authors found that in preserved clear, Se-enriched kiwifruit juice, there was a significant decrease in TPC of 5.2%, while in the cloudy version, there was a minimal increase of 0.5%. UHT preservation caused a significant decrease in quercetin content in tomato juice, while there were no significant changes in chlorogenic or caffeic acid contents [18]. Researchers confirm that the phenolics contents of preserved samples decreased during storage, which may be related to oxidation degradation [35]. Following preservation at 110 °C/8.6 s and refrigerated storage for 25 days, the TPC decreased by 90.7% [42]. However, less degradation of phenolics was reported by Liu et al. [44], at about 17.0% and 25.2% at 4 °C and 25 °C, respectively. It is emphasized that thermal inactivation of enzymes can also lead to the retention of a significant portion of anthocyanins in a sample immediately after preservation, as well as during storage. Also, further condensation of breakdown products with organic acids or carbohydrates can cause a decrease in the contents of these bioactive components [27,37,39,83,84]. In pomegranate juice there was a 29.3% decrease in TPC [70], and in mulberry juice there was a decrease of less than 4% [27]. Some researchers state that the anthocyanin content decreased during storage by 75.3% after 25 days of storage at 4 °C in pepper and orange juice blend [42] and by 7.8% and 34.1% during 12 weeks of storage of purple sweet potato nectar at 4 °C and 25 °C, respectively [35].

The HTST technique can perform significant extraction of phenolics from a raw food matrix. In sea blackthorn juice, there was a 6.6% increase in TPC following preservation at 100 °C for 15 s due to cell disruption [56]. In peach juice, preservation by HTST resulted in an increase from 617.2 mg (raw juice) to 1000.3 mg GAE/L (72 °C/15 s). An upward trend was also shown during storage (by 11.4% over 28 days) but to a significantly lesser extent than in raw juice (by 140.3% over 28 days) [31]. In addition, an increase in TPC content was also shown by Mena et al. [57]. Also, studies have been described in which phenolics are largely degraded [5] or only slightly, like in lemonade and citrus juice by 3.6% and 7.6%, respectively [64]. Morales-de la Peña et al. [82] observed, after the HTST process, a decrease in the phenolic acids content of less than 3%, and, on the other hand, an increase in flavonoids of 61.5%. Nonsignificant changes in TPC and total ellagitannin content in an HTST-preserved (71.1 °C/3 s) blackberry–soy–flaxseed beverage were observed by Bonilla et al. [67]. A significant decrease of 27.5% in total monomeric anthocyanins content was shown by Yuan et al. [70]. Despite the differences in the preservations of phenolics, their degradation occurred during prolonged storage as a result of heating in different food matrices and using different parameters [88]. A different conclusion was reached by Morales-de la Peña et al. [82], who noted increases in phenolic acids and decreases in the flavonoid contents in an HTST-preserved fruit-juice–soymilk beverage during 56 days of storage. Deng et al. [5] showed a relatively stable TPC during storage (Table 3). No significant effect of HTST on anthocyanins was observed by Mena et al. [57] in pomegranate–lemon juice and pomegranate juice because of the short processing time (90 °C/5 s). In addition, a decrease in anthocyanin content of 27.6% was reported by Yuan et al. [70].

4.3.3. Other Bioactive Substances

Xu et al. [25] showed a small decrease of 4.9% in the selenium content of clear Se-enriched kiwifruit juice preserved in parameters of 110 °C/8.6 s, while there was a significant decrease in this element on level of 25% in cloudy juice. The content of chlorophyll, the compound responsible for the attractive and green color of kiwifruit and the juices derived from them, also dropped significantly, by 80.9% and 47.8%, respectively. The researchers found that such a change is related to the thermal denaturation of a protein in chlorophylls. Bioactive compounds that also determine the color of products, and have antioxidant properties, are carotenoids. Chen et al. [39], Wang et al. [18] and Liu et al. [44] showed that heating under conditions of 110 °C/8.6 s did not change the content of carotenoids. It can lead to isomerization of various compounds and the formation of new compounds that were absent before the preservation process, such as the cis-13-lycopene in tomato juice [18]. In lettuce juice preserved by UHT (115 °C/5 s), there were significant decreases in the total chlorophyll content by 14.1% and total β-carotene content by 35.5% [12]. The same researchers observed also a significant decrease in vitamins E, K1, B6, B9 and B12, and negligible decreases in B1 and B3, and a negligible increase in B2. Mesta-Vicuña et al. [40] indicate degradation of betacyanins and betaxanthins by 63.1% and 45%, respectively, as a result of heating at 80 °C for 30 s. These thermal conditions result in a 14.2% increase in gingerol content due to disruption of plant cells and higher extraction of the inner compounds [38].

Thermal processing causes isomerization of carotenoids and can result in a reduction in their content, for example, of 20.5% in sea buckthorn juice preserved with HTST [56]. On the other hand, heating can cause their extraction through cell wall degradation or the formation of new carotenoid compounds, as well as concentrating the sample and thus the bioactive components [88]. Mesta-Vicuña et al. [40] indicated degradation of betacyanins and betaxanthins by 14.8% and 14.4%, respectively, following heating at 80 °C for 30 s (Table 3).

Table 3. Effect of HTST processing on the content of selected bioactive compounds.

Matrix	Parameters	Phenolic Compounds	Vitamins	Other Bioactive Ingredients	References
Fruit juice–soymilk beverage	90 °C/60 s	Total phenolic acids 2.8% ↓ *, caffeic acid 11.6% ↑ *, chlorogenic acid 19.4% ↓ *, coumaric acid 2.7% ↓ *, ferulic acid 29.1% ↑ *, sinapic acid 13.0% ↓ *, TFC 61.5% ↑ *, hesperidin 590.1% ↑ *, rutin 43.0% ↓ *, narirutin 22.5% ↑ *, quercetin 16.6% ↑ *, apigenin 31.3% ↓	-	Cis-violacanthin + antheraxanthin 8.3% ↓, cis-antheraxanthin 17.4% ↓, lutein 38.9% ↓ *, zeaxanthin 26.3% ↓, α-cryptoxanthin 25.0% ↓, β-cryptoxanthin 23.8% ↓ *, α-carotene 0% and β-carotene 16.3% ↓	[82]
Orange juice	90 °C/20 s	-	Vitamin A 16.9% ↑	TCC 12.6% ↓, neoxanthin+9-cis-violaxanthin 21.1% ↓, antheraxanthin 14.8% ↑, lutein 12.1% ↓, zeaxanthin 17.9% ↓, isolutein 6.8% ↓, β-cryptoxanthin 14.6% ↓, α-carotene 34.1% ↓, 9-cis-α-carotene 24.1% ↓, phytoene + phytofluene 7.7% ↓ and 7,8,7’,8’-tetrahidrolycopene 9.9% ↓, 9.7% ↓ and 17.5% ↓	[89]
Tomato juice	90 °C/30 s 90 °C/60 s	TPC 1.1% ↑ and 0%, chlorogenic acid 0.5% ↑ and 0.7% ↑, ferulic acid 1.1% ↑ and 1.1% ↓, p-coumaric acid 0% and 3.1% ↓, caffeic acid 0% and 4.7% ↑, quercetin 3.9% ↓ and 3.4% ↓, kaempferol 1.8% ↓ and 0%	Vitamin A 2.0% ↑ and 5.1% ↑	TCC 2.1% ↑ * and 2.1% ↑ *, lycopene 4.6% ↑ * and 7.2% ↑ *, neurosporene 2.3% ↓ * and 5.4% ↓ *, γ-carotene 5.6% ↓ * and 3.4% ↓ *, ζ-carotene 5.0% ↓ and 5.0% ↓, phytofluene 6.2% ↑ * and 5.4% ↑ * and phytoene 2.4% ↓ * and 11.6% ↓ *	[88]
Clarified and cloudy pomegranate juices	90 °C/5 s	Total monomeric anthocyanin content 1.2% ↓ and 40.8% ↓ * TPC—no difference	-	-	[81]
Sea buckthorn juice	100 °C/15 s	TPC 6.5% ↑ *	Vitamin C 14.3% ↓ *	TCC 20.5% ↓ *	[56]
Acerola juice, acerola juice + inulin, acerola juice + gluco-oligosaccharides	90 °C/2 s	-	Vitamin C ↑ *	-	[76]
Nonconcentrated and concentrated sea buckthorn juice	100 °C/15 s	TPC—no significant difference	Vitamin C—no significant difference	-	[30]
Cloudy apple juice	98 °C/50 s	TPC 22.7% ↓ *	-	-	[5]
Strawberry juice	72 °C/15 s	TPC 3.4% ↑	Vitamin C 0.6% ↑	-	[26]
Açai juice	90 °C/6 s	TPC—↓ * Anthocyanins—no significant difference	Vitamin C—no significant difference	-	[51]
Lemonade Citrus juice Green juice	75 °C/90 s	TPC 3.6% ↓, 7.6% ↓ and 0.5% ↑	Vitamin C 91.7% ↓ * Vitamin C 12.1% ↓ * Vitamin C—nondetected in raw and processed	-	[64]
Orange juice	90 °C/60 s	TPC 19.0% ↓ * TFC 14.7% ↑, narirutin 10.8% ↓, hesperidin 28.8% ↑ *, eriocitrin 6.3% ↓, eriodictyol 12.5% ↓, naringenin 9.6% ↓, hesperetin 14.3% ↓ and kaempferol 39.6% ↑ *	L-ascorbic acid 20.1% ↓ * Vitamin A 39.6% ↓ *	TCC 40.8% ↓ *, lutein 21.7% ↓, zeaxanthin 24.0% ↓ *, β-cryptoxanthin 32.3% ↓ *, α-carotene 42.5% ↓ * and β-carotene 39.0% ↓ *	[90]
Orange juice	92 °C/30 s 85 °C/15 s	Total flavones 0.3% ↓ and 0.2% ↑, vicenin-2 2.0% ↑ and 1.8% ↑, apigenin-d 2.3% ↓ and 0.9% ↑, total flavanones 7.4% ↑ and 4.6% ↑, naringin-d 5.7% ↑ and 4.3% ↑, narirutin 0.4% ↑ and 4.3% ↑, hesperidin 7.9% ↑ and 4.5% ↑, didymin 11.2% ↑ and 9.2% ↑ and TFC 6.9% ↓ and 4.3% ↓	-	TCC 16.6% ↓ * and 10.1% ↓ *, (Z)-antheraxanthin isomers 20.0% ↓ and 13.3% ↓, all-(E)- violaxanthin + (Z)- violaxanthin isomers 31.4% ↓ * and 20.0% ↓, (Z)-luteoxanthin isomer 0% and 2.6% ↑, (9Z)-violaxanthin + (Z)-antheraxanthin isomer 17.0% ↓ and 13.1% ↓, (Z)-luteoxanthin isomer 23.7% ↓ * and 15.3% ↓, lutein 2.0% ↓ and 3.9% ↑, zeaxanthin 24.0% ↓ * and 18.0% ↓ *, (9Z)- or (9 Z)-antheraxanthin 20.6% ↓ and 12.2% ↓, zeinoxanthin 21.6% ↓ and 16.2% ↓, β-cryptoxanthin 14.9% ↓ and 7.9% ↓, α-carotene 16.7% ↓ and 8.3% ↓, β-carotene 13.0% ↓ and 4.3% ↓ and phytoene 17.5% ↓ and 10.5% ↓	[91]
Cloudy apple juice	72 °C/15 s 85 °C/30 s	-	Vitamin C ↓ * and ↓ *	-	[74]
Orange juice	72 °C/20 s	-	Dehydroascorbic acid ↓ * Ascorbic acid—no significant difference	TCC –no significant difference	[4]
Pomegranate juice (MW—Mollar de Elche varietal juice + Wonderful varietal juice, ML—Mollar de Elche + lemon juice, M100—Molar de Elche)	90 °C/5 s	Anthocyanins 6.6% ↓, 2.5% ↓ and 3.7% ↑ Punicalagins 80% ↑ *, 866.7% ↑ * and 975% ↑ * Punicalagin-like 18.2% ↓, 1.6% ↑ and 27.5% ↓ * Punicalin 4.5% ↑, 27.7% ↓ and 3.0% ↓ Ellagic acid 2.7% ↓, 39.4% ↓ * and 12.1% ↓	Vitamin C 59.6% ↓ *, 31.5% ↓ * and 12.9% ↑	-	[57]
Red prickly pear juice	80 °C/30 s	TPC 2.0% ↓	-	Betacyanins 14.8% ↓ * Betaxanthins 14.4% ↓ *	[40]
Peach juice	72 °C/15 s	TPC 62.1% ↑ *	Ascorbic acid 22.0% ↓ *	-	[31]
3 Beverages varied in terms of ingredients (blackberry juice, soy beverage, ground flaxseed, water, stabilizer and sweetener)	71.1 °C/3 s	TPC 3.2% ↑, 8.0% ↓ and 0.2% ↓ Total ellagitannin 2.9% ↓, 15.4% ↓ and 7.4% ↑ Cyanidin-3-O-glucoside 11.4% ↑, 8.3% ↓ and 15.6% ↑ Cyanidin-3-O-malonyl-glucoside 2.4% ↓, 17.8% ↓ and 3.2% ↓ Daidzein 3.4% ↑, 17.5% ↓ and 5.5% ↓ Genistein 11.9% ↑, 9.9% ↓ and 8.5% ↑ Secoisolariciresinol 14.9% ↑, 1.5% ↓ and 9.5% ↓	-	-	[67]
Cloudy pomegranate juice	85 °C/30 s	Total monomeric anthocyanins content 27.5% ↓ * Cyanidin-3-O-glucoside ↑ Cyanidin-3,5-O-diglucoside ↓ * Delphinidin-3-O-glucoside ↓ Delphinidin-3,5-O-diglucoside ↓ Afzelechin-delphinidin-3-O-hexoside ↑ Pelargonidin-3-O-glucoside ↓ Pelargonidin-3,5-O-diglucoside ↓ *	Vitamin C 19.8% ↓ *	-	[70]
Pomegranate fermented beverage	72 °C/15 s	TPC 14.1% ↓ TFC 3.4% ↓ Total anthocyanins content 17.5% ↓ *	-	-	[58]
Orange juice	76.8 °C/15 s	-	Vitamin C—no significant difference	-	[78]
Raspberry juice	85 °C/60 s 85 °C/20 s	Lamberirianin C 3.9% ↓ and 7.3% ↓ Sanguiin H-6 3.7% ↓ and 7.5% ↓ Ellagic acid conjugate 1 1.4% ↓ and 4.2% ↓ Ellagic acid conjugate 2 53.0% ↑ * and 47.1% ↑ * Ellagic acid conjugate 3 21.1% ↓ * and 22.8% ↓ * Ellagic acid 4.3% ↓ and 4.3% ↓ Cyanidin-3-O-sophoroside 7.0% ↓ and 9.0% ↓ Cyanidin-3-O-rutinoside 7.7% ↓ and 10.1% ↓	-	-	[92]
Blueberry juice	95 °C/15 s	TPC 1.1% ↓ Anthocyanin 9.2% ↓	Vitamin C 18.5% ↓ *	-	[49]
Orange juice	70, 80, 90 and 100 °C, time 2, 5, 10, 15 and 30 s	-	Vitamin C—for all temperatures ↓; for 70 °C/10 s 8% ↓, 80 °C/10 s 13% ↓, 90 °C/10 s 15% ↓ and 100 °C/10 s 18% ↓	-	[14]
Apple juice with raspberry	85 °C/6 s	TPC ↓, total flavonoids ↓	-	-	[13]
Juice from “Baya Marisa” or “Golden Delicious” apples	85 °C/30 s	Total hydroxycinnamic acids 42.0% ↓ * and 64.3% ↓ * Total hydroxybenzoic acids 33.6% ↓ * and nondetected in “Golden Delicious” apples Total dihydrochalcones 32.9% ↓ and 2.0% ↓ Total flavanols 79.5% ↓ * and 72.2% ↓ * Total anthocyanins 66.5% ↓ * and nondetected in “Golden Delicious” apples TPC 52.0% ↓ * and 63.7% ↓ *	-	-	[93]
Orange juice	90 °C/20 s	TPC 5.3% ↓	Vitamin C 0.1% ↓	TCC 12.6% ↓	[94]
Strawberry puree–kale juice mix	72 °C/60 s	Total anthocyanins content ↓	-	-	[61]
Whey–grape juice drink	72 °C/15 s	Total anthocyanins content 8.5% ↓, monomeric anthocyanins 25.0% ↓ and polymeric anthocyanins 2.0% ↓	-	-	[95]
Valencia orange juice	73.9 °C/30 s 92.2 °C/31 s	-	Ascorbic acid 3.8% ↓ and 2.6% ↓	Total carotenes 5.5% ↑ and 14.0% ↓ TCC 8.5% ↑ and 13.6% ↓ Total carotenoid fatty acids esters 7.7% ↑ and 15.1% ↓ α-carotene 12.5% ↑ and 7.1% ↓ β-carotene 20.6% ↑ and 4.1% ↑	[96]
Orange juice	90 °C/60 s	-	Vitamin C 17.6% ↓	-	[97]
Apple and cranberry juice blend	72 °C/26 s	TPC 3.0% ↓ Cyanidin-3-O-glucoside 14.6% ↓	-	-	[98]

↑—Increase; ↓—decrease. * Statistically significant change. TPC—total phenolic content; TFC—total flavonoid content; TCC—total carotenoid content.

Table 3. Effect of HTST processing on the content of selected bioactive compounds.

Matrix	Parameters	Phenolic Compounds	Vitamins	Other Bioactive Ingredients	References
Fruit juice–soymilk beverage	90 °C/60 s	Total phenolic acids 2.8% ↓ *, caffeic acid 11.6% ↑ *, chlorogenic acid 19.4% ↓ *, coumaric acid 2.7% ↓ *, ferulic acid 29.1% ↑ *, sinapic acid 13.0% ↓ *, TFC 61.5% ↑ *, hesperidin 590.1% ↑ *, rutin 43.0% ↓ *, narirutin 22.5% ↑ *, quercetin 16.6% ↑ *, apigenin 31.3% ↓	-	Cis-violacanthin + antheraxanthin 8.3% ↓, cis-antheraxanthin 17.4% ↓, lutein 38.9% ↓ *, zeaxanthin 26.3% ↓, α-cryptoxanthin 25.0% ↓, β-cryptoxanthin 23.8% ↓ *, α-carotene 0% and β-carotene 16.3% ↓	[82]
Orange juice	90 °C/20 s	-	Vitamin A 16.9% ↑	TCC 12.6% ↓, neoxanthin+9-cis-violaxanthin 21.1% ↓, antheraxanthin 14.8% ↑, lutein 12.1% ↓, zeaxanthin 17.9% ↓, isolutein 6.8% ↓, β-cryptoxanthin 14.6% ↓, α-carotene 34.1% ↓, 9-cis-α-carotene 24.1% ↓, phytoene + phytofluene 7.7% ↓ and 7,8,7’,8’-tetrahidrolycopene 9.9% ↓, 9.7% ↓ and 17.5% ↓	[89]
Tomato juice	90 °C/30 s 90 °C/60 s	TPC 1.1% ↑ and 0%, chlorogenic acid 0.5% ↑ and 0.7% ↑, ferulic acid 1.1% ↑ and 1.1% ↓, p-coumaric acid 0% and 3.1% ↓, caffeic acid 0% and 4.7% ↑, quercetin 3.9% ↓ and 3.4% ↓, kaempferol 1.8% ↓ and 0%	Vitamin A 2.0% ↑ and 5.1% ↑	TCC 2.1% ↑ * and 2.1% ↑ *, lycopene 4.6% ↑ * and 7.2% ↑ *, neurosporene 2.3% ↓ * and 5.4% ↓ *, γ-carotene 5.6% ↓ * and 3.4% ↓ *, ζ-carotene 5.0% ↓ and 5.0% ↓, phytofluene 6.2% ↑ * and 5.4% ↑ * and phytoene 2.4% ↓ * and 11.6% ↓ *	[88]
Clarified and cloudy pomegranate juices	90 °C/5 s	Total monomeric anthocyanin content 1.2% ↓ and 40.8% ↓ * TPC—no difference	-	-	[81]
Sea buckthorn juice	100 °C/15 s	TPC 6.5% ↑ *	Vitamin C 14.3% ↓ *	TCC 20.5% ↓ *	[56]
Acerola juice, acerola juice + inulin, acerola juice + gluco-oligosaccharides	90 °C/2 s	-	Vitamin C ↑ *	-	[76]
Nonconcentrated and concentrated sea buckthorn juice	100 °C/15 s	TPC—no significant difference	Vitamin C—no significant difference	-	[30]
Cloudy apple juice	98 °C/50 s	TPC 22.7% ↓ *	-	-	[5]
Strawberry juice	72 °C/15 s	TPC 3.4% ↑	Vitamin C 0.6% ↑	-	[26]
Açai juice	90 °C/6 s	TPC—↓ * Anthocyanins—no significant difference	Vitamin C—no significant difference	-	[51]
Lemonade Citrus juice Green juice	75 °C/90 s	TPC 3.6% ↓, 7.6% ↓ and 0.5% ↑	Vitamin C 91.7% ↓ * Vitamin C 12.1% ↓ * Vitamin C—nondetected in raw and processed	-	[64]
Orange juice	90 °C/60 s	TPC 19.0% ↓ * TFC 14.7% ↑, narirutin 10.8% ↓, hesperidin 28.8% ↑ *, eriocitrin 6.3% ↓, eriodictyol 12.5% ↓, naringenin 9.6% ↓, hesperetin 14.3% ↓ and kaempferol 39.6% ↑ *	L-ascorbic acid 20.1% ↓ * Vitamin A 39.6% ↓ *	TCC 40.8% ↓ *, lutein 21.7% ↓, zeaxanthin 24.0% ↓ *, β-cryptoxanthin 32.3% ↓ *, α-carotene 42.5% ↓ * and β-carotene 39.0% ↓ *	[90]
Orange juice	92 °C/30 s 85 °C/15 s	Total flavones 0.3% ↓ and 0.2% ↑, vicenin-2 2.0% ↑ and 1.8% ↑, apigenin-d 2.3% ↓ and 0.9% ↑, total flavanones 7.4% ↑ and 4.6% ↑, naringin-d 5.7% ↑ and 4.3% ↑, narirutin 0.4% ↑ and 4.3% ↑, hesperidin 7.9% ↑ and 4.5% ↑, didymin 11.2% ↑ and 9.2% ↑ and TFC 6.9% ↓ and 4.3% ↓	-	TCC 16.6% ↓ * and 10.1% ↓ *, (Z)-antheraxanthin isomers 20.0% ↓ and 13.3% ↓, all-(E)- violaxanthin + (Z)- violaxanthin isomers 31.4% ↓ * and 20.0% ↓, (Z)-luteoxanthin isomer 0% and 2.6% ↑, (9Z)-violaxanthin + (Z)-antheraxanthin isomer 17.0% ↓ and 13.1% ↓, (Z)-luteoxanthin isomer 23.7% ↓ * and 15.3% ↓, lutein 2.0% ↓ and 3.9% ↑, zeaxanthin 24.0% ↓ * and 18.0% ↓ *, (9Z)- or (9 Z)-antheraxanthin 20.6% ↓ and 12.2% ↓, zeinoxanthin 21.6% ↓ and 16.2% ↓, β-cryptoxanthin 14.9% ↓ and 7.9% ↓, α-carotene 16.7% ↓ and 8.3% ↓, β-carotene 13.0% ↓ and 4.3% ↓ and phytoene 17.5% ↓ and 10.5% ↓	[91]
Cloudy apple juice	72 °C/15 s 85 °C/30 s	-	Vitamin C ↓ * and ↓ *	-	[74]
Orange juice	72 °C/20 s	-	Dehydroascorbic acid ↓ * Ascorbic acid—no significant difference	TCC –no significant difference	[4]
Pomegranate juice (MW—Mollar de Elche varietal juice + Wonderful varietal juice, ML—Mollar de Elche + lemon juice, M100—Molar de Elche)	90 °C/5 s	Anthocyanins 6.6% ↓, 2.5% ↓ and 3.7% ↑ Punicalagins 80% ↑ *, 866.7% ↑ * and 975% ↑ * Punicalagin-like 18.2% ↓, 1.6% ↑ and 27.5% ↓ * Punicalin 4.5% ↑, 27.7% ↓ and 3.0% ↓ Ellagic acid 2.7% ↓, 39.4% ↓ * and 12.1% ↓	Vitamin C 59.6% ↓ *, 31.5% ↓ * and 12.9% ↑	-	[57]
Red prickly pear juice	80 °C/30 s	TPC 2.0% ↓	-	Betacyanins 14.8% ↓ * Betaxanthins 14.4% ↓ *	[40]
Peach juice	72 °C/15 s	TPC 62.1% ↑ *	Ascorbic acid 22.0% ↓ *	-	[31]
3 Beverages varied in terms of ingredients (blackberry juice, soy beverage, ground flaxseed, water, stabilizer and sweetener)	71.1 °C/3 s	TPC 3.2% ↑, 8.0% ↓ and 0.2% ↓ Total ellagitannin 2.9% ↓, 15.4% ↓ and 7.4% ↑ Cyanidin-3-O-glucoside 11.4% ↑, 8.3% ↓ and 15.6% ↑ Cyanidin-3-O-malonyl-glucoside 2.4% ↓, 17.8% ↓ and 3.2% ↓ Daidzein 3.4% ↑, 17.5% ↓ and 5.5% ↓ Genistein 11.9% ↑, 9.9% ↓ and 8.5% ↑ Secoisolariciresinol 14.9% ↑, 1.5% ↓ and 9.5% ↓	-	-	[67]
Cloudy pomegranate juice	85 °C/30 s	Total monomeric anthocyanins content 27.5% ↓ * Cyanidin-3-O-glucoside ↑ Cyanidin-3,5-O-diglucoside ↓ * Delphinidin-3-O-glucoside ↓ Delphinidin-3,5-O-diglucoside ↓ Afzelechin-delphinidin-3-O-hexoside ↑ Pelargonidin-3-O-glucoside ↓ Pelargonidin-3,5-O-diglucoside ↓ *	Vitamin C 19.8% ↓ *	-	[70]
Pomegranate fermented beverage	72 °C/15 s	TPC 14.1% ↓ TFC 3.4% ↓ Total anthocyanins content 17.5% ↓ *	-	-	[58]
Orange juice	76.8 °C/15 s	-	Vitamin C—no significant difference	-	[78]
Raspberry juice	85 °C/60 s 85 °C/20 s	Lamberirianin C 3.9% ↓ and 7.3% ↓ Sanguiin H-6 3.7% ↓ and 7.5% ↓ Ellagic acid conjugate 1 1.4% ↓ and 4.2% ↓ Ellagic acid conjugate 2 53.0% ↑ * and 47.1% ↑ * Ellagic acid conjugate 3 21.1% ↓ * and 22.8% ↓ * Ellagic acid 4.3% ↓ and 4.3% ↓ Cyanidin-3-O-sophoroside 7.0% ↓ and 9.0% ↓ Cyanidin-3-O-rutinoside 7.7% ↓ and 10.1% ↓	-	-	[92]
Blueberry juice	95 °C/15 s	TPC 1.1% ↓ Anthocyanin 9.2% ↓	Vitamin C 18.5% ↓ *	-	[49]
Orange juice	70, 80, 90 and 100 °C, time 2, 5, 10, 15 and 30 s	-	Vitamin C—for all temperatures ↓; for 70 °C/10 s 8% ↓, 80 °C/10 s 13% ↓, 90 °C/10 s 15% ↓ and 100 °C/10 s 18% ↓	-	[14]
Apple juice with raspberry	85 °C/6 s	TPC ↓, total flavonoids ↓	-	-	[13]
Juice from “Baya Marisa” or “Golden Delicious” apples	85 °C/30 s	Total hydroxycinnamic acids 42.0% ↓ * and 64.3% ↓ * Total hydroxybenzoic acids 33.6% ↓ * and nondetected in “Golden Delicious” apples Total dihydrochalcones 32.9% ↓ and 2.0% ↓ Total flavanols 79.5% ↓ * and 72.2% ↓ * Total anthocyanins 66.5% ↓ * and nondetected in “Golden Delicious” apples TPC 52.0% ↓ * and 63.7% ↓ *	-	-	[93]
Orange juice	90 °C/20 s	TPC 5.3% ↓	Vitamin C 0.1% ↓	TCC 12.6% ↓	[94]
Strawberry puree–kale juice mix	72 °C/60 s	Total anthocyanins content ↓	-	-	[61]
Whey–grape juice drink	72 °C/15 s	Total anthocyanins content 8.5% ↓, monomeric anthocyanins 25.0% ↓ and polymeric anthocyanins 2.0% ↓	-	-	[95]
Valencia orange juice	73.9 °C/30 s 92.2 °C/31 s	-	Ascorbic acid 3.8% ↓ and 2.6% ↓	Total carotenes 5.5% ↑ and 14.0% ↓ TCC 8.5% ↑ and 13.6% ↓ Total carotenoid fatty acids esters 7.7% ↑ and 15.1% ↓ α-carotene 12.5% ↑ and 7.1% ↓ β-carotene 20.6% ↑ and 4.1% ↑	[96]
Orange juice	90 °C/60 s	-	Vitamin C 17.6% ↓	-	[97]
Apple and cranberry juice blend	72 °C/26 s	TPC 3.0% ↓ Cyanidin-3-O-glucoside 14.6% ↓	-	-	[98]

↑—Increase; ↓—decrease. * Statistically significant change. TPC—total phenolic content; TFC—total flavonoid content; TCC—total carotenoid content.

4.4. Antioxidant Activity

Antioxidant activity (AA) is closely related to the contents of bioactive components found in food, such as phenolics, as well as their bioaccessibility and bioavailability. The literature points to numerous methods for determining total antioxidant activity in foods based on single-electron transfer reaction or SET assays or based on a hydrogen atom transfer reaction or HAT assays [79].

Heating alters the content and profile of bioactive compounds found in plant raw materials and, consequently, as well as antioxidant activities. A study by Chen et al. [39] conducted on a papaya beverage showed that the AA measured by FRAP and DPPH radical methods decreased significantly immediately after preservation (110 °C/8.6 s), while there was no change in carotenoids content and a decrease in total phenols content, which are strong antioxidants. Decreases in antioxidant activities were shown by Chen et al. [38] (8.2% for DPPH radical and 6.8% for FRAP) and Chen et al. [37] (10.2% for DPPH radical and 6.0% for FRAP), with a significant decrease in TPC, and by Gao et al. [53] in red grapefruit juice (1.4% for DPPH radical and 8.5% for FRAP), as well as other researchers [17,42]. On the other hand, Zou et al. [27] observed no significant change in AA using the DPPH radical method but noted a significant increase using the FRAP method immediately after preservation. In the second case, the phenomena was associated with an increase in TPC and the tendency of phenolics to undergo polymerization reactions. The opposite relationship was shown by Liu et al. [44]. Wang et al. [35] indicated neither an increase nor a decrease in AA after preservation of purple sweet potato nectar by the UHT method, which was associated with no change in phenolics content, while over 12 weeks of storage, AA decreased by more than 20%. Zhao et al. [54] observed no significant change in AA despite significant decreases in TPC and ascorbic acid content. A decrease in AA during storage was also demonstrated by Liu et al. [44].

HTST under conditions of 72 °C/15 s resulted in a significant (77.5%) increase in antioxidant activity immediately after treatment. Over the course of preservation, the AA in the preserved sample increased from 1554.64 (0 day) to 2489.16 μmol TE/L (28 day). However, from 14 to 28 days of preservation, the AA in heated peach juice was lower than in a nonprocessed one [31]. Yildiz and Aadil [26] came to similar conclusions, as follows: in strawberry juice immediately after the process, AA increased by 27% and was significantly higher by the 7th day of storage compared to fresh juice. In contrast, the AA values for ultrasound or high-pressure homogenized juices were significantly higher throughout the working principles of these processes [26,31]. On the other hand, the AA was not affected by thermal processing [30,57]. In contrast, some researchers point to a significant reduction in AA due to decreases in antioxidants, such as vitamin C and carotenoids, in sea buckthorn juice as a result of HTST [56].

4.5. Enzymes Activity

Preservation using high temperatures results in a significant reduction in the activity or complete inactivation of enzymes responsible for changes in the quality characteristics and sensory attributes of food. The higher the temperature, the lower the enzymatic activity remains [37]. The application of appropriate heat treatment can lead to complete inactivation of enzymes (Table 4). The main enzymes found in raw fruits and vegetables are polyphenyl oxidase (PPO), peroxidase (POD), pectinomethylesterase (PME) and phenylalanine ammonia lyase (PAL). They are responsible for numerous reactions, most often leading to changes in quality characteristics [20]. PPO and POD are enzymes largely responsible for enzymatic browning reactions in fruits and vegetables (undesirable brown color). Their action also leads to an unpleasant taste and a loss of nutritional properties [99]. PAL is responsible for the biosynthesis of phenolic compounds in plants, converting phenylalanine into flavonoids, phenolic acids or anthocyanins [84]. PME causes cloud loss by allowing for calcium pectates to precipitate and clarify the juice [4,31]. Enzyme inactivation usually involves the destruction of secondary and tertiary structures by physical (heat, ultrasound, and high pressure) and chemical factors [2].

In the storage process, changes in enzyme activity can occur. For example, changes in phenolic enzyme (PPO and POD) activity can arise because of reactions between phenolic compounds and proteins or phenolics oxidation. The first reaction leads to the formation of an inactive enzyme–substrate complex or a change in the enzyme’s catalytic site. The second leads to a reduction in the amount of substrate and the formation of products that inhibit enzymes [74].

The combination of temperature and exposure time can affect enzyme inactivation differently. A detailed summary of the effects of the applied UHT and HTST preservation temperatures on enzymatic activity in juices, nectars and beverages is included in Table 4. Wang et al. [24] showed that UHT conditions of 120 °C/2 s and 135 °C/2 s resulted in more than a 10% PPO residual rate in watermelon juice, while 110 °C/2 s resulted in about a two times higher PPO residual rate. Because of the residual PPO activity in the juice, an inverse relationship occurred in the phenolics content. PPO is responsible for catalyzing the o-hydroxylation of o-phenols and o-diphenols. Juices preserved at 120 °C and 135 °C for two seconds did not differ in phenolics content from nonpreserved juices, while juice treated at 110 °C had significantly lower levels of phenolics. Prolonged exposure to high temperature can effectively increase the inactivation of tissue enzymes. Huang et al. [20] demonstrated the complete inactivation of PPO and POD in apricot nectar, Krapfenbauer et al. [100] of PPO in cloudy apple juice, and Gao et al. [53] of POD and PME in red grapefruit juice using 110 °C/8.6 s. In contrast, the 110 °C/8.6 s treatment caused the complete inactivation of PPO and the half inactivation of PAL in red raspberry juice, while POD activity remained at the same level [84].

The HTST preservation process caused a significant reduction in the activity or complete inactivation of tissue enzymes [20]. Yildiz [31] showed that under conditions of 72 °C/15 s, decreases of 13.6% and 13.0% in PPO and PME activities occurred, respectively, compared to raw juice. During 28 days of storage, PPO and PME activities in the HTST juices increased by 16.7% and 19.4%. Similar changes were observed for PPO in raw juice; however, PME increased by 99.7%. With the HTST process, we can obtain a product with less turbidity and change in color during storage, which is important in consumer evaluations. In addition, Wibowo et al. [74] showed that conditions of 72 °C/15 s caused inactivation of PPO, POD and PME by more than 90% in apple juice. Also, significant inactivation of PPO and POD was demonstrated by the treatment described in [101]. Even better results were achieved by Wibowo et al. [74]; they obtained complete inactivation of PPO, POD and PME using conditions of 85 °C/15 s, while Deng et al. [5] deactivated PPO and POD using the same parameters.

Another important enzyme found in fruits and vegetables is lipooxygenase (LOX). Polyunsaturated fatty acids undergo oxygenation catalyzed by LOX. This enzyme also plays an important role in shaping plant flavors. Heating 85 °C/15 s allowed for the residual activity of LOX to reach 58.2% in cucumber juice drink, while the enzyme activity decreased during storage [66]. Aguiló-Aguayo et al. [100] indicated that the LOX activities of strawberry juices preserved at 90 °C for 60 and 30 s were 37.7% and 45.3%, respectively [102]. Aguiar et al. [103] developed enzymic time–temperature integrators (TTIs) with rapid detection for the evaluation of continuous HTST pasteurization processes, using temperatures of 70–85 °C and times of 10–60 s.

Table 4. Effects of UHT and HTST processing on enzymatic activity in different beverages.

Matrix	Parameters	Enzymes—Residual Activities	Reference
UHT
Mango nectar	110 °C/8.6 s	Acid invertase 8.6% *	[45]
Watermelon juice	110 °C/2 s, 120 °C/2 s, 135 °C/2 s	For 120 °C and 135 °C, 2 times lower residual activity of PPO than at 110 °C	[24]
Red grapefruit juice	110 °C/8.6 s	PPO, POD and PME—completely inactivated	[53]
Apricot nectar	110 °C/8.6 s	PPO, POD and PME—completely inactivated	[20]
red raspberry juice	110 °C/8.6 s	PAL ↓ *; PPO—completely inactivated; PPO—equal to that of fresh juice	[84]
HTST
Strawberry juice	90 °C/60 s 90 °C/30 s	22.2% * for PME, 76.2% * for PG 48% * for PME and 96.8% * for PG	[104]
Strawberry juice	90 °C/60 s 90 °C/30 s	Lipoxygenase 37.7% * and 45.3% *, b-glucosidase—slight increase in activity 7.9% and 4.1%	[102]
Sea buckthorn juice	100 °C/15 s	SOD 51.3% *	[56]
Orange and carrot juice	98 °C/21 s	PME—2% *	[46]
Cloudy apple juice	98 °C/50 s	PPO and POD—completely inactivated	[5]
Cloudy apple juice	72 °C/15 s 85 °C/30 s	PPO, POD and PME—up to 10% * PPO, POD and PME—completely inactivated	[74]
Orange juice	72 °C/20 s	PME 15% *; POD—completely inactivated	[4]
Peach juice	72 °C/15 s	PPO 86.4%; PME 87.0%	[31]
Orange juice	70, 80, 90 and 100 °C and time 2, 5, 10, 15 and 30 s	PME—inactivation of 99% was only achieved at 90 °C and 100 °C	[14]

↓—decrease. * Statistically significant change. PPO—polyphenol oxidase; POD—peroxidase; PAL—phenylalanine ammonia-lyase; PME—pectinmethylesterase; SOD—superoxide dismutase.

Table 4. Effects of UHT and HTST processing on enzymatic activity in different beverages.

Matrix	Parameters	Enzymes—Residual Activities	Reference
UHT
Mango nectar	110 °C/8.6 s	Acid invertase 8.6% *	[45]
Watermelon juice	110 °C/2 s, 120 °C/2 s, 135 °C/2 s	For 120 °C and 135 °C, 2 times lower residual activity of PPO than at 110 °C	[24]
Red grapefruit juice	110 °C/8.6 s	PPO, POD and PME—completely inactivated	[53]
Apricot nectar	110 °C/8.6 s	PPO, POD and PME—completely inactivated	[20]
red raspberry juice	110 °C/8.6 s	PAL ↓ *; PPO—completely inactivated; PPO—equal to that of fresh juice	[84]
HTST
Strawberry juice	90 °C/60 s 90 °C/30 s	22.2% * for PME, 76.2% * for PG 48% * for PME and 96.8% * for PG	[104]
Strawberry juice	90 °C/60 s 90 °C/30 s	Lipoxygenase 37.7% * and 45.3% *, b-glucosidase—slight increase in activity 7.9% and 4.1%	[102]
Sea buckthorn juice	100 °C/15 s	SOD 51.3% *	[56]
Orange and carrot juice	98 °C/21 s	PME—2% *	[46]
Cloudy apple juice	98 °C/50 s	PPO and POD—completely inactivated	[5]
Cloudy apple juice	72 °C/15 s 85 °C/30 s	PPO, POD and PME—up to 10% * PPO, POD and PME—completely inactivated	[74]
Orange juice	72 °C/20 s	PME 15% *; POD—completely inactivated	[4]
Peach juice	72 °C/15 s	PPO 86.4%; PME 87.0%	[31]
Orange juice	70, 80, 90 and 100 °C and time 2, 5, 10, 15 and 30 s	PME—inactivation of 99% was only achieved at 90 °C and 100 °C	[14]

↓—decrease. * Statistically significant change. PPO—polyphenol oxidase; POD—peroxidase; PAL—phenylalanine ammonia-lyase; PME—pectinmethylesterase; SOD—superoxide dismutase.

4.6. Hydroxymethylfurfural

At high temperatures, Maillard reactions take place, leading to the formation of compounds such as hydroxymethylfurfural (HMF) and furfural. The reactions occur between amino acids and reducing sugars, in addition to ascorbic acid transformations. HMF and others are compounds characterized by genotoxic, cytotoxic and mutagenic risks [4,19,45,47]. The allowed maximum level of 10 mg for HMF per liter of juice are recommended by the AIJN (European Fruit Juice Association) [74].

Liu et al. [45] showed that heating at 110 °C/8.6 s increased the HMF content in mango nectar by 70.6% compared to nonpreserved juice. They also observed an increase in its content in UHT-preserved samples after 16 weeks of 55.2% at 4 °C and 177.8% at 25 °C. In apricot nectar subjected to UHT, HMF was not detected [20].

Varied changes are observed in the literature for the HMF content in samples preserved by the HTST method. Wibowo et al. [74] indicated that in orange juice pasteurized by the HTST method, HMF was not immediately detected after the process; however, it started to accumulate after 20 weeks of storage at 20 °C, 8 weeks at 28 °C, 3 weeks at 35 °C and 4 days at 42 °C. The researchers reported that the appearance of HMF may have been related to a change in the composition of the sugars present in the product. Tests on orange juice were also performed by Ağçam et al. [19] using the parameters of 90 °C/10 s and 90 °C/20 s. The HMF contents immediately after preservation were 1.7 and 4.7 ppb, respectively; at the same time, this compound was not observed in the raw sample. During 180 days of storage, increases of 1315.6% and 826.7% were observed. Aguiló-Aguayo et al. [104] noted significant increases of 50.6% and 77.1% in the HMF content of strawberry juice after preservation at 90 °C/30 s and 90 °C/60 s, while no significant changes occurred during storage for 63 days at 4 °C. A statistically insignificant increase in the amount of HMF, as a result of HTST, was demonstrated by Cortés et al. [69]. Rivas et al. [46] observed no effect of HTST on HMF content compared to raw and pulsed electric field preserved samples. In addition, the same researchers showed no significant changes in HMF content during storage at 2 °C for 10 weeks. In a study by Vervoort et al. [4], no measurable quantities of HMF were found under the HTST-processing conditions applied.

4.7. Volatile Compounds

Volatile compounds determine the aroma and flavor of foods. Their transformations can lead to organoleptic changes that are unacceptable to consumers.

As a result of UHT preservation, the neral content increased, while the geranial content decreased in cloudy ginger juice [37]. Also, Wang et al. [24] showed the degradation of typical volatile contents of watermelon juice (C9 alcohol and C9 aldehyde) by 15.4%, 10.9% and 10.1% after applying the conditions of 110 °C, 120 °C and 135 °C for 2 s, respectively. However, higher temperatures (120 °C and 135 °C) reduced the ADH activity and had a greater degrading effect on the C9 alcohol content rather than C9 aldehyde content. Wang et al. [43] investigated different preservation methods in watermelon juice. The typical volatile contents of UHT juice (135 °C/2 s) were significantly lower than those in unprocessed juice. The heated samples showed the presence of two compounds (acetic acid, 2-methyl butyric acid), which were absent in the raw sample. Liu et al. [105], in watermelon juice processed at 126 °C/15 s, noticed an increase in the relative contents of esters (58.4%) and aldehydes but a decrease in alcohols (80.1%), ketones (59.5%) and alkanes compared to raw juice. Nonanal and 3,7-dimethyl-2,6-octadienal (characteristic compounds for watermelon flavor) decreased by 59.2% and 92.1% in UHT watermelon juice. In the UHT juice, the content of amyl butyrate increased (80.1%), accounting for the “cooking flavor”. Also, Wang et al. [18] pointed to the formation of the compound dimethyl sulfide, responsible for the “cooked flavor” of tomato juice, following heating at 110 °C/8.6 s. In addition, in raw tomato juice, the contents of alcohols, aldehydes, and ketones accounted for 46%, 18% and 23% of all flavor compounds, respectively, whereas in juice after UHT they were 36%, 34% and 18%, respectively. Liu et al. (2022) [28] indicated that UHT has the effect of raising the contents of the esters and ketones responsible for the specific flavor of melon juice, while it causes a decrease in the contents of alcohols, aldehydes and total volatile components. Zhao et al. [54] indicated that 20 volatile compounds were present in the control sample, but following UHT (110 °C/8.6 s), only 13 remained in korla pear juice. In comparison, there were 17 compounds in the HPP-preserved sample. Liu et al. [41] compared the UHT and HPP processes in an analysis of the key odorants of clear cucumber juice. In the case of (Z)-6-nonenal and (E,Z)-3,6-nonandien-1-ol, there was no significant difference between the processed and raw juices. (E,Z)-2,6-nonadienal and (E)-2-nonenal showed significant increases in their contents after preservation but to a much lesser extent in the UHT sample than in the HPP one. Other observations made by Bao et al. [17] included that the heating of black carrot juice at 130 °C/5 s did not change the overall odor profile.

Zhu et al. [49] compared blueberry juice after HTST and PEF preservation, indicating that the decreases in the compounds were considerably lower for PEF than with the HTST method, particularly in esters. HTST causes the aroma of blueberry juice to be less diverse. Passion fruit juice also showed HTST-preserved volatile compounds to a lesser extent than when using the HHP preservation technique. The concentrations of esters, alcohols, ketones and hydrocarbons decreased in the HTST sample by 23.9, 44.2, 12.5 and 39.7%, respectively [11]. The volatile acidities of a pomegranate fermented beverage, as a result of heating at 72 °C for 15 s, did not change significantly compared to the nonprocessed sample, while PEF and traditional pasteurization significantly lowered them [58]. A study by Atuonwu et al. [78] indicated that it was not possible to distinguish between the microwave- and HTST-treated samples of orange juice. Tian et al. [32] compared HPP, HTST (85 °C/30 s) and UHT (110 °C/8.6 s) in terms of the volatiles compounds of cloudy pomegranate juice. Alcohols were more sensitive to thermal sterilization than other kinds of volatile compounds. The UHT and HTST methods preserved volatile compounds to a lesser extent because of the direct effect of the thermal treatments on the small-molecule flavor compounds. For the same reason, linalool was observed in the HTST and UHT samples in contrast to the pressurized and raw samples. In addition, a significant increase in the content of a pentadecanoic acid (131.1% for HTST and 228.8% for UHT), a compound responsible for the waxy aroma and off-odor of cloudy pomegranate juices, was observed in the high-temperature-treated samples.

4.8. Sensory Quality

Highly significant is the impact of preservation methods on sensory qualities. The high temperatures lead to changes in the contents of various ingredients, transformations of substances and occurrences of chemical processes that change the taste, smell and color of products.

Xu et al. [25] evaluated the quality of selenium-enriched kiwi juice treated at 110 °C for 8.6 s. They showed that clear and cloudy preserved juices received significantly lower scores for color and appearance, flavor and overall acceptability compared to their raw counterparts. Only for taste was there no significant difference among trained panelists. In addition, in all distinguishing factors, thermally preserved juices were rated worse than HPP-treated juices. Chen et al. [39] came to different conclusions; the UHT-preserved papaya beverage did not differ in color and appearance, while it had worse mouth feel, flavor and overall acceptability compared to raw juice. In contrast, raw clear cucumber juice did not differ in color and appearance from the UHT sample [41]. When stored, cucumber juices received lower scores after 20 days than immediately after preservation. Liu et al. [41] and Xu et al. [25] showed that thermally preserved juices scored lower than HPP juices in all distinguishing factors.

de Souza et al. [64] conducted sensory evaluations of lemonade, citrus juice and green juice. The HTST-preserved lemonade scored better in flavor and overall liking than the raw sample, and the preserved green juice scored worse in overall liking and more than 30% worse in color than raw juice. In contrast, the preserved citrus juice was not significantly different from its untreated version. The researchers also sensory evaluated those products preserved by other methods—mostly, the HPP method and UV-C light changed the ratings to a lesser extent compared to HTST. Rivas et al. [46] found that juice subjected to HTST preservation showed less acceptable odor and taste than samples subjected to PEF preservation. Walkling-Ribeiro et al. [50] compared orange juice preserved at 94 °C/26 s and a sample preserved with a combined thermosonification/PEF method. The panelists found no significant differences between these samples in terms of color, odor, sweetness, acidity, flavor and acceptability. However, the HTST-preserved juice was rated as being blander than the TS/PEF juice by twice as many evaluators. Deshaware et al. [16] found that an increase in the processing temperature for the same product can result in poorer flavor scores among evaluators. The HTST-preserved orange juice was rated worse overall and in terms of flavor and aroma than fresh juice; however, even lower scores were given to the UHT-preserved sample [22]. Polydera et al. [106], based on sensory evaluations, determined the shelf-life of orange juice, which they indicated as being 60 days at 0 °C and 47 days at 5 °C. This is about one-third to one-half shorter times than when HPP treatment was used, indicating a lower level of preservation of the product’s relevant sensory attributes.

5. Conclusions

The HTST and UHT methods are promising methods in the fruit and vegetable industry. The ability to modify the processing parameters can allow for the selection of adequate preservation parameters for individual products and better results than other unconventional methods, such as HPP or PEF. HTST and UHT are methods characterized by the ability to inactivate unwanted microorganisms, allowing for product shelf-lives that last for many weeks.

In the case of basic physicochemical characteristics, such as total soluble solids, pH or acidity, the HTST and UHT methods most often do not determine significant changes that negatively affect the quality of the final product. In the case of color, contents of bioactive components and the antioxidant and enzymatic activities it is significantly important to choose the right temperature and duration. Excessively high temperatures or exposure times can lead to the degradation of key bioactive components, such as vitamins, carotenoids or phenolic compounds, while the right choice of parameters can allow these compounds to be extracted from the food matrix, transformed or, at least, to remain at similar levels as in raw samples. Accordingly, the transformation of natural colorants due to heat leads to changes in the absolute color, which can be important in consumer evaluations. The HTST and UHT methods show highly effective inactivation of enzymes such as POD, PPO or PME, allowing for better quality of products to be preserved including during storage. In the case of volatile compounds, these thermal methods most often lead to changes in their profiles, leading to flavor and aroma degradation to some extent.

It is presumed that in the near future the HTST and UHT methods will be dynamically improved upon on an industrial scale in the fruit and vegetable industry because of their numerous benefits compared to the traditional pasteurization process commonly used in the industry. Better retention of bioactive components, less sensory degradation and equally or even more effective inactivation of microorganisms, as well as lower financial costs of these processes are the most important advantages in the rapid heating of food. A challenge for the described preservation methods is to investigate their application in terms of adapting process parameters to products with varying raw material particle sizes, such as beverages enriched with different raw materials or multivegetable soups with solid pieces. A little-developed area of research is the application of HTST and UHT in a combined method, for example with HPP.