Techno-Functional Properties and Recent Advances in the Manufacturing of Whey Beverages: A Review

Abstract

Whey is mostly generated during the production of cheese or curds. Nevertheless, the quantity of whey generated is substantial, with just fifty percent of the total utilised. Moreover, improper disposal of whey has a negative impact on the environment. The use of whey in beverage production is an innovative approach with the potential to expand the application possibilities of this by-product of the food industry. The article focuses on the composition and health benefits of whey, while the impact of improper disposal of whey into wastewater and the environmental impact are discussed. Included is a description of the production and properties of unfermented and fermented whey beverages. Finally, new technological processes used in the production of whey-based beverages are discussed.

1. Introduction

The dairy industry is perpetually increasing its production, resulting in the substantial production of whey as a valuable by-product. Hence, proper processing of whey is crucial, as its composition may present a risk to the environment if not disposed of appropriately. Inappropriate disposal of whey may alter the physicochemical characteristics of the soil, potentially diminishing crop yield. Moreover, the discharge of whey into wastewater may reduce dissolved oxygen levels, consequently endangering aquatic ecosystems [1,2].

Bovine milk is widely regarded as one of the most versatile foods for humans, either consumed in its natural form or as an ingredient in various dairy products. Nowadays, a range of products are derived from milk, including liquid milk, cheese, yogurt, powdered milk products, and various additives such as protein-rich products and lactose. Additionally, fermented milk, butter, and cream-based products are also popular. In 2020, Europe produced nearly 148 million tons of milk, with close to 50% of this amount allocated for cheese [3,4]. During cheese production, up to 90% of the milk volume is converted to whey. Additionally, whey is divided into two main groups—sweet and acid whey, respectively. Sweet whey is primarily generated during cheese production, whereas acid whey is predominantly developed in the production of quark cheese (acid-coagulated cheese) or yogurt. Sweet whey, in particular, has become the largest volume by-product in the dairy industry and contains valuable components with nutritional and technological properties, such as proteins, lactose, and minerals. Advances in technology have further enhanced the value of sweet whey, expanding its applications in the food industry [3,5,6].

Furthermore, whey is widely recognised as a valuable source of highly nutritious and biologically active proteins, along with other organic compounds. Notably, whey protein accounts for approximately 20% of the total protein content in bovine milk. These proteins possess exceptional functional properties (foaming, emulsification, water-binding, and gelation properties). Due to these unique characteristics, whey protein products are increasingly sought after as food additives [7,8,9]. Recent advances in whey processing technologies, such as ultrafiltration, microfiltration, and enzyme treatments, have unlocked new potentials for whey utilisation. These innovations allow for the production of high-purity whey protein isolates (WPI) and other specialised products, catering to a growing market demand for whey-based ingredients [10].

However, whey is often regarded as a production waste and, in many cases, is combined with water from cleaning processes before being discharged to wastewater treatment plants and may be associated with serious environmental problems [11]. It is reported that only 50% of the sweet whey produced is further processed for food production. Fifty percent of this amount is used directly in liquid form, for example, in the production of ricotta cheese and whey-based fermented beverages. Approximately 30% of the processed whey volume is converted into powder, which can be used for producing infant formula; 15% is purified and sold as lactose and its by-products, while the remaining portion is utilised for whey protein concentration or isolation [11,12,13].

As the dairy industry expands, the environmental and economic challenges associated with whey disposal and management become increasingly significant. This review explores not only the functional and nutritional properties of whey but also recent innovations that address these challenges. In particular, this review will examine the techno-functional properties of whey, discuss the latest manufacturing methods and technologies, and explore recent trends in the development of whey beverages. By addressing both the opportunities and challenges, this paper aims to provide a comprehensive understanding of whey’s role in the beverage industry and its potential for future applications in manufacturing whey-based beverages.

2. Whey: Nutritional Value and Health Benefits

Whey is a yellow-green liquid, coloured by riboflavin (vitamin B2) remaining after the removal of caseins and fat from milk, containing lactose, soluble salts, and globular proteins. Depending on the type of coagulation, however, two distinct types of whey can be produced. Firstly, there is sweet whey, which is generated when rennet enzymes (primarily chymosin) act on milk caseins. This enzymatic coagulation process is especially common in cheese production, and the pH of sweet whey is typically around 5.9–6.6. In contrast, acidic whey forms either through fermentation or by the addition of organic acids (such as citric, acetic, or lactic acid) or mineral acids (such as hydrochloric or sulfuric acid), and the pH of acid whey is 4.3–4.6. Acid whey is often a by-product of acid-coagulated cheeses, such as quark cheese and ricotta, as well as Greek yogurt [14,15,16]. There are differences between sweet and acid whey not only in pH value but also in composition. Comparison of composition of sweet and acid whey is provided in

Table 1. Composition (g·L⁻¹) of sweet and acid whey [16].

Composition (g·L−1)	Sweet Whey	Acid Whey
Total solids	5.72–8.50	5.20–5.90
Ash	0.50–0.65	0.60–0.80
Lactose	3.06–5.02	3.00–4.60
Total protein	0.60–1.20	0.20–0.50
Fat	0.05–0.40	0.01–0.32
Lactic acid	0.14–0.28	0.50–0.60
Ca	0.03–0.06	0.09–0.14
K	0.08–0.16	0.10–0.14
Mg	0.01–0.02	0.01–0.02
Na	0.02–0.32	0.02–0.05
Citrate	0.06–0.07	0.07–0.09
Phosphate	0.06–0.07	0.06–0.10

.

The composition and properties of whey vary according to the type of milk, the type of animal’s diet, the technology used to process the milk, and other environmental factors [17]. Whey contains, on average, approximately 93% water. Acid whey possesses a higher ash content. On the other hand, it contains reduced lactose content and hence increased lactic acid, as lactic acid bacteria convert lactose into lactic acid during the curd formation process. In sweet coagulating, the activity of lactic cultures is diminished compared to the coagulation caused by rennet, resulting in a lower concentration of lactic acid in the sweet whey. Importantly, acidic coagulation of casein occurs close to the isoelectric point of milk (pH ≈ 4.6), resulting in a higher degree of milk protein precipitation than in sweet whey. The lower pH of the acid whey results in the dissolution of the colloidal calcium phosphate from the casein micelles, therefore, the calcium content of the acid whey is almost twice as high [13,14,16,18,19].

As already mentioned, whey was previously considered mainly as waste and was primarily used as part of animal feed. Nevertheless, due to technological developments in the dairy industry and current research, whey is now considered a value-added raw material [5,18]. Whey contains components with high nutritional value and biological activity. First of all, these are whey proteins, which can have a beneficial effect on growth, metabolism, and health. Lack of protein in the diet causes health problems worldwide, so it is advisable to include foods rich in these nutrients in the human diet. Whey proteins, as globular proteins, contain a high proportion of α-helix structures. Hydrophilic and hydrophobic amino acids, as well as acidic and basic amino acids, are evenly distributed in their polypeptide chain [20,21].

Whey proteins have an amino acid composition that closely resembles the amino acids of human muscle tissue. In particular, they are distinguished by their high proportion of essential amino acids and branched-chain amino acids (BCAA)—valine, leucine, and isoleucine—making them superior to all other protein sources of both animal and plant origin [22]. Moreover, approximately 14% of whey protein occurs as hydrolysates (comprising single amino acids, dipeptides, tripeptides, and polypeptides), which enhance digestion and are crucial for the production of many physiologically active compounds [23].

The Food and Agriculture Organisation of the United Nations (FAO) has developed a methodology called DIAAS (Digestible Indispensable Amino Acid Score), which emphasises the importance of protein quality. This system evaluates the quality of food protein based on three main criteria: protein content, the representation of essential amino acids (AA), and their digestibility [24]. The FAO DIAAS study recommends the categorisation of proteins according to quality classifications based on the DIAAS value: <75 (no quality claim); 75–99 (high-quality protein); and ≥100 (excellent quality protein) [25]. Whey proteins are categorised as high-quality proteins with an average DIAAS of 75 or higher. Nonetheless, the DIAAS value may be affected by purity and the manufacturing method. Liquid sweet whey possesses a DIAAS value of approximately 90, whereas whey protein concentrate (WPC) exhibits a DIAAS value ranging from 110 to 134, and whey protein isolate has a DIAAS value of 125 [5,25].

The whey protein content is influenced by many factors, including whey type, milk type, lactation stage, diet, and possibly processing technology [26]. The most important fractions of whey proteins are α-lactalbumin (α-LA), β-lactoglobulin (β-LG), bovine serum albumin (BSA), immunoglobulins (IG), bovine lactoferrin (BLF), bovine lactoperoxidase (LP), and smaller amounts of glycomacropeptide (GMP) [27]. In addition, sweet whey contains caseinmacropeptide (CMP), which is formed during the breakdown of κ-casein by rennet [28].

Enzymatic hydrolysis of whey protein in the human digestive system, as well as fermentation of milk by starter cultures or hydrolysis by plant or microbial proteases, leads to the release of bioactive peptides. These bioactive peptides then function as signalling molecules and have diverse physiological effects on the immune, gastrointestinal, cardiovascular, and nervous systems. A growing body of scientific evidence supports the valuable effects of whey proteins on human health, including antimicrobial, antioxidant, antihypertensive, antidiabetic, and immunomodulatory effects, while they may also contribute to weight loss and alleviate or inhibit allergic reactions [29,30].

Lactose in whey plays a crucial role in ensuring optimal magnesium levels and enhancing the digestion of dairy fats and other nutrients within the human body while also not contributing to dental plaque formation. Additionally, the heat treatment of whey leads to the transformation of a portion of lactose into lactulose, which serves as a growth stimulant for bifidobacteria [21,31].

Water-soluble vitamins found in milk also transfer into whey, although their concentrations fluctuate considerably and are strongly affected by whey storage conditions. Whey comprises significant quantities of riboflavin, folic acid, and cobalamin, with the latter two attaching to whey proteins and frequently persisting in the whey post-cheese manufacture. Whey may possess elevated concentrations of riboflavin compared to milk, attributable to the action of certain lactic acid bacteria utilised in cheese manufacturing [21].

3. Impact of Wastewater from Cheese Production on the Environment

Sweet whey, previously deemed a waste byproduct, has been transformed into a valuable raw resource with considerable market potential owing to technological breakthroughs and research. This advancement has enabled the creation of value-added components, thus accelerating market growth for these goods relative to other dairy constituents [5]. Cheese production is environmentally demanding, mainly due to the high amount of whey, which is often considered waste. The whey is mixed with wash water from the plant and ends up in the wastewater treatment plants. This wastewater can vary according to the final product, the type of system, and the operating methods used. Generally, it consists of various concentrations of milk or processed dairy products, in addition to wash water that contains both alkaline and acidic chemicals used during the cleaning of bottles, tanks, and processing equipment, including tools and pumps [11,13].

Characteristic indicators of wastewater include Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) values [32]. The Chemical Oxygen Demand (COD) of cheese whey can vary significantly, typically ranging between 50.000 and 80.000 mg/L, while its Biological Oxygen Demand (BOD) generally falls within 40.000 to 60.000 mg/L. Whey represents a waste load that is 100–175 times greater than the equivalent volume of domestic wastewater [28]. The rapid depletion of oxygen in soil, caused by the breakdown of proteins and sugars in whey, presents a substantial disposal issue, especially given the high volumes involved [32,33]. Wastewater from cheese and casein production is notable for its high levels of these indicators, as dairy wastewater contains a high concentration of organic substances, such as serum proteins, milk sugar (lactose), mineral salts (calcium, magnesium, phosphorus, and sodium), and milk fat [11].

Mawson [34] describes three methods of handling acid whey: direct use or disposal (e.g., as animal feed or a food ingredient), direct stabilisation (physical or chemical treatments to improve stability against microbial degradation), and conversion processes (the transformation of lactose into other compounds through biotransformation or chemical reactions).

4. Whey-Based Beverages

Whey is produced as a by-product of cheese production and has experienced a growing application in the manufacture of both non-fermented and fermented whey-based beverages over the past decade. Whey beverages signify an innovative method of utilising whey for human intake. These whey-based beverages can be enhanced with nutraceutical components, probiotics, and prebiotics. Simultaneously, these beverages may be combined with fruit juices or milk. The drawback of the technological procedure, typically involving heat treatment, is heat-induced sedimentation. Consequently, non-thermal processing techniques can be integrated into the production process, thereby maintaining the nutritional value of the beverages [35]. The origin of whey and its possible use are shown in Figure 1.

Fermented whey beverages are suitable for a broader range of consumers, primarily due to their low lactose content and reduced allergenicity. Moreover, compared to non-fermented whey drinks, fermented whey beverages offer extended shelf life, higher levels of phenolic compounds, and enhanced antioxidant activity [26]. The diagram of the production of fermented whey beverages is shown in Figure 2.

Nonetheless, whey may possess undesirable organoleptic characteristics, particularly the flavour of acid whey, and concurrently, it may exhibit an unpleasant astringency. Astringency is characterised as “complex sensations due to shrinking, drawing or puckering of the epithelium as a result of exposure to substances such as alums or tannins” [14,36,37].

Various flavouring ingredient combinations enhance or mask the organoleptic qualities of whey-based beverages. The most frequently utilised components are fruit or, less often, vegetable derivatives, such as concentrates, juices, syrups, pulps, or nectars [37,38]. Moreover, chocolate, cocoa, vanilla, and various cereals (such as rice, oats, or barley) were utilised to enhance the flavour of whey beverages [21]. Different forms of whey can be used to make whey beverages, whether it is liquid whey, whey powder, whey protein concentrate (WPC), or whey protein isolate (WPI) [39].

Figure 2. Fermented whey-based beverage production process diagram [40].

Figure 2. Fermented whey-based beverage production process diagram [40].

4.1. Nonfermented Whey-Based Beverages

A study performed by Djurić [37] examined the development of whey beverages using various fruit components. This study involved the production of whey beverages using orange, pear, peach, and apple juices at concentrations of 2%, 4%, and 6%. The study examined the influence of different fruit juice solid concentrations on the organoleptic characteristics of the beverages. An increased fruit juice concentration enhanced the overall acceptance of whey beverages. The beverage with 6% orange juice received favourable reviews for its refreshing quality; however, lower juice concentrations produced unfavourable flavour profiles. The combination of whey and peach juice received the highest overall rating. The addition of orange juice to the whey drinks did not cover the whey flavour, and the whey drinks exhibited a higher sediment content. Similarly, whey drinks flavoured with pear juice had a higher sediment content, which negatively affected the appearance of the whey beverages. The flavour improved with increasing pear juice content. The whey beverages containing apple juice were distinguished by unacceptable taste, aroma, and appearance.

For the production of whey-based beverages, a combination with orange juice is very common. For instance, Sady et al. [41] compared a standard orange beverage with an orange beverage enriched with whey. The data obtained revealed that orange beverages containing whey exhibited higher levels of proteins, glucose, ash content, and vitamin B12. Nonetheless, they showed lower levels of sucrose, fructose, and vitamin C, as well as reduced antioxidant activity. On the other hand, higher addition of whey negatively impacted the organoleptic properties of the beverage.

Chatterjee et al. [42] investigated beverages with different proportions of concentrated whey, orange juice (40%, 50%, and 60%), and sugar (7% w/v, 8% w/v, and 9% w/v). At the same time, the effect of the addition of a preservative (sodium benzoate) on the shelf life of whey-based beverages at room (30 ± 2 °C) and refrigeration (7 ± 1 °C) temperature was investigated. The product with 40% orange juice and 8% sugar added showed the most favourable organoleptic properties. The presence of preservatives prolonged the shelf life of the whey-based drinks. When stored at room temperature, the shelf life of the beverage without preservative was 5 days, and it was 11 days for the beverage with preservative. In contrast, at refrigerated temperature, shelf life was 49 days and 91 days without and with preservatives, respectively.

The combination of WPI and whey protein hydrolysate (WPH) with apple juice was investigated by Goudarzi et al. [43]. The findings showed that a decreasing fruit juice content negatively affected the organoleptic properties of beverages containing WPI, whereas no significant differences in taste were observed in beverages containing WPH. Additionally, beverages with a higher pH were rated more favourably.

Moreover, Cruz et al. [44] examined an unusual combination of whey and acerola juice. Three formulations of whey and acerola juice were developed in the proportions of 50% v/v whey to 50% v/v acerola juice, 70% v/v whey to 30% v/v acerola juice, and 30% v/v whey to 70% v/v acerola juice. Whey-based beverages exhibited favourable organoleptic properties and, thanks to the addition of acerola, acted as an important source of vitamin C. The whey drink with 70% acerola juice contained the most vitamin C, however, it also contained the most sediment. Nevertheless, the higher sediment content did not affect the acceptability of the beverage, therefore, the whey-based beverage with 70% v/v acerola juice was the best rated.

A rather unconventional combination of whey with passion fruit, melon, and Indian gooseberry juices was investigated by Gimhani and Liyanage [45]. Significant differences were observed among the three beverages in terms of sedimentation, colour, aroma, taste, and overall acceptability. The whey beverage with added passion fruit juice was highest rated, as the passion fruit juice effectively masked the undesirable taste and aroma of whey.

Pasteurised sheep whey was also used to produce whey beverages, with mango, pineapple, and tropical fruit flavours, in a study by Nedanovska et al. [46]. Physicochemical, microbiological, and sensory properties of model samples were evaluated during the 15-day storage. The beverages contained a significant amount of sediment, which decreased during storage. The aggregation of whey protein is mainly due to the heat treatment and pH of the sample. The reduced pH value during storage presumably enhanced the surface charge of denatured whey proteins, resulting in the dissolution of the initially produced sediment. A mixture of whey and tropical fruit was the best evaluated sample. Microbiological analysis indicated an increased presence of microorganisms, possibly related to contamination during the storage period.

Diverse varieties of fruit are utilised in the manufacture of whey-based beverages. These predominantly encompass citrus fruits, including oranges, lemons, and grapefruits. Conventional fruits such as apples and pears are frequently utilised, among other varieties, including mangoes, bananas, and papayas. Moreover, various berries such as blueberries, strawberries, raspberries, blackberries, and mulberries are frequently included [47,48,49,50,51,52]. There are beverages that contain vegetable juices. Examples of such beverages may include, among other ingredients, the addition of carrot juice, pumpkin juice, or parsley juice [53].

4.2. Fermented Whey-Based Beverages

The production of fermented whey beverages is another relatively attractive method of utilising all whey. Due to its high lactose content, whey serves as a suitable medium for the cultivation of lactic acid bacteria, yeasts, or kefir cultures. During fermentation, the breakdown of lactose, peptides, and fats occurs through the action of microbial enzymes, leading to the formation of lactic acid, alcohols, and other sensory-active compounds. These compounds can contribute to the specific organoleptic profile of the beverages while extending their shelf life. Examples include acetaldehyde, ethyl acetate, isoamyl alcohol, isobutanol, 1-propanol, isopentyl alcohol, and 1-hexanol, which have been identified using high-performance liquid chromatography [16,54,55,56,57].

Lactic acid bacteria (Pediococcus pentosaceus, Lactiplantibacillus plantarum) used in the production of fermented whey beverages are capable of inhibiting pathogenic bacteria. As a result, these beverages may help reduce cholesterol levels and increase antioxidant activity [58].

In the work of León-López et al. [59], hydrolysed collagen (0.30%, 0.50%, 0.75%, and 1%) was added to fermented whey beverages. Specifically, fermentation was carried out using lactic acid bacteria (Lacticaseibacillus rhamnosus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus delbrueckii, and Streptococcus thermophilus). Beverages with the addition of 1% hydrolysed collagen were found to contain 9.75 ± 0.20 g/L of protein. Moreover, as the concentration of hydrolysed collagen increased, the viscosity of the beverages also rose significantly. Furthermore, the beverages enriched with hydrolysed collagen demonstrated antimicrobial properties, as no undesirable pathogenic microbiota were detected. In addition to these benefits, the nutritional value of the beverages due to the high protein concentration and no changes in the fat and lactose concentrations were also enhanced. Furthermore, the in vitro bioavailability of hydrolysed collagen exhibited elevated absorption rates attributable to its low molecular weight.

Furthermore, Legarová and Kouřimská [60] examined the commercial potential of whey beverages combined with 25% and 50% semi-skimmed milk addition and fermented using yogurt cultures. The study also compared unfermented and fermented whey-based beverages. The culture contained lactic acid bacteria, specifically Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. No significant changes in acidity were observed between samples fermented for 3 or 4 h; however, a significant difference was identified between whey drink samples with and without milk addition. Based on the results, the fermentation by yoghurt culture did not yield statistically significant enhancements in the organoleptic properties of the whey drink; however, the incorporation of milk emerged as the primary factor affecting not only the overall sensory quality of the whey drinks but also their flavour, appearance, colour, viscosity, and homogeneity.

Aly et al. [61] produced whey beverages with different concentrations of cactus pear (10, 20, and 30%) and kiwi (10 and 20%) juice fermented with Lactiplantibacillus plantarum. The quality, viability of microorganisms, and organoleptic properties of the beverage were monitored over a period of 20 days. The concentration or type of the fruit component did not have a significant effect on the viability of Lactiplantibacillus plantarum. During fermentation, the pH value of the model samples decreased. After 20 days of the experiment, the beverages exhibited higher antioxidant activity and an increased content of phenolic compounds. Based on the sensory analysis, the samples with a 30% fruit component addition were rated as the best.

Dinkçi et al. [62] focused on the production of probiotic beverages using WPC derived from cow, sheep, and goat milk. The beverages were fermented with Streptococcus thermophilus, along with the probiotic bacteria Lactobacillus acidophilus and Bifidobacterium animalis subsp. lactis. Additionally, the beverages were flavoured with kiwi powder. The use of WPC increased the protein content of the beverages. Furthermore, the type and origin of WPC significantly influenced the quality of the probiotic beverages, as they contained higher levels of free amino acids, including essential and branched-chain amino acids. The beverages also contained a substantial amount of phenolic compounds and exhibited high antioxidant activity.

A probiotic whey beverage enriched with spirulina (0.25%, 0.50%, and 0.75% (w/w)) was also studied by Elkot et al. [63]. Additionally, the beverages were flavoured with lemon and mint juice. Spirulina (Arthrospira platensis), a microalga, is known for its numerous positive effects, such as its use in the prevention and treatment of hypercholesterolemia, cardiovascular diseases, and diabetes. Spirulina possesses a high fibre and protein content and serves as an agent to preserve the textural quality of products by enhancing sensory attributes and improving rheological properties. The probiotic culture used for producing the beverages consisted of Streptococcus thermophilus, Lactobacillus acidophilus, and Bifidobacterium spp. The probiotic beverages were stored under refrigeration temperature (4 ± 1 °C) for 21 days. During storage, the content of vitamins, minerals, antioxidants, and phenolic compounds in the beverages increased while their probiotic properties were successfully maintained. The use of 0.50% (w/w) spirulina markedly enhanced the structural properties and sensory value of the final product.

AbdulAlim et al. [64] developed a probiotic whey beverage flavoured with black mulberry juice (25, 50, and 75%). A drink without black mulberry juice containing 100% whey and a drink containing 100% black mulberry juice were also prepared. Selected physicochemical, microbiological, and sensory properties of fermented whey-based beverages were monitored during 21 days of storage at 4 ± 1 °C. The vitality of the probiotic bacteria Lacticaseibacillus rhamnosus and Bifidobacterium animalis ssp. lactis was sustained for 14 days but diminished after 21 days. An increased fruit content enhanced antioxidant activity; nevertheless, both antioxidant activity and phenolic component levels decreased during the experiment. Based on sensory analysis, fermented whey beverages received favourable ratings; however, the drink with 75% black mulberry juice was deemed as the best.

The sensory and rheological properties of probiotic whey beverages were studied by Castro et al. [65]. The latter properties can be influenced by the presence of additives, fermentation time, and the amount of whey. In the study, beverages with varying concentrations of whey in the sample (0%, 20%, 35%, 50%, 65%, and 80% v/v) were prepared, flavoured with 2% v/v strawberry juice, and fermented with Lactobacillus acidophilus. Replacing casein with whey protein increased gel brittleness. In the sensory evaluation, the sample containing 65% v/v whey was rated the best.

The study conducted by Nursiwi et al. [66] investigated a unique combination of probiotic whey beverage and tomato juice. Fermentation was conducted utilising the probiotic microorganisms Lactobacillus acidophilus and Lactiplantibacillus plantarum. Tomato juice was included in quantities of 5%, 10%, and 15%. The physicochemical and organoleptic properties of fermented whey-based beverages were evaluated during 18 h of fermentation. Based on the data obtained, it was found that the beverage with 18% tomato juice showed the highest antioxidant activity; on the other hand, the whey beverage with 5% tomato juice was the most acceptable in the sensory evaluation.

Another method for creating fermented whey beverages involves the utilisation of kefir starter culture [67,68,69,70]. The microorganisms present in kefir starter culture include Lactobacillus kefiranofaciens, Lentilactobacillus kefiri, Lentilactobacillus parakefiri, Lactococcus lactis, Kluyveromyces marxianus, Saccharomyces unisporus, and Saccharomyces cerevisiae. The research conducted by Londero et al. [67] established that the ideal fermentation temperature for kefir starter culture is 20 °C. At elevated temperatures, notably 30 °C and 37 °C, the growth rate diminished, and the morphology of the kefir grains altered. Despite fermented milk, fermented whey exhibited a reduced quantity of lactic acid bacteria and an elevated quantity of yeasts.

The microbial composition of the fermented whey beverage was examined in the study by Magalhães et al. [71]. The most abundant microorganisms were yeasts Kluyveromyces marxianus, Saccharomyces cerevisiae, and Kazachstania unispora, along with bacteria of the Lactobacillus genus. This combination of microorganisms means that kefir-fermented whey beverages can be classified as probiotics.

The effect of fermentation temperature (20–30 °C) and the amount of kefir grains (2–8% w/v) on the phenolic content and antioxidant activity of fermented whey drinks flavoured with apple juice was investigated in a study by Sabokbar et al. [72]. Using a response surface methodology, the study suggested that the beverage exhibiting the highest antioxidant activity and total phenolic compound content would contain 7.56% (w/v) kefir grains fermented at a temperature of 24.82 °C.

Rejdlová et al. [73] investigated the use of both kefir grains and water kefir grains. The study compared the physicochemical, rheological, and sensory properties of beverages fermented with either milk kefir grains or water kefir grains, with varying concentrations of carrot juice (65% (w/w), 75% (w/w), 85% (w/w), and 95% (w/w) of carrot juice). Based on the rheological analysis, a potential influence of whey content on the flow properties of the beverage was observed; however, no significant differences were found between the two starter cultures applied. Similarly, in the sensory analysis, the beverages containing 75% (w/w) carrot juice were evaluated as the most favourable, regardless of the starter culture used.

The use of water kefir grains for the production of fermented whey-based beverages was also explored in a subsequent study performed by Rejdlová et al. [40], where whey-based beverages were flavoured with varying amounts of black currant juice (addition of 10 and 20% w/w blackcurrant juice). At the same time, the influence of the 0.25% (w/w) and 0.50% (w/w) hydrocolloid (furcellaran) addition on the properties of the beverage was monitored using rheology and mechanical vibration damping techniques. It was found that samples containing 0.50% (w/w) furcellaran exhibited a higher amount of sediment compared to those with 0.25% (w/w). After 48 h of fermentation, the samples contained 0.92–4.86% (v/v) ethanol. The study confirmed that all model samples exhibited non-Newtonian behaviour, and the sample containing 20% (w/w) black currant juice was rated the best.

5. Technological Processes Used in Whey-Based Beverages Manufacturing

Various technological processes can be employed in the production of dairy beverages, which may impact the properties of the product. These processes can lead to a reduction in the nutritional value of whey proteins, such as denaturation and aggregation, and can also decrease the digestibility and bioavailability of these proteins. Therefore, it is crucial to select an appropriate technology that minimises negative effects on the proteins [74].

At the same time, unconventional technologies are being studied, including intensive ultrasound, cold plasma, microwave, and ohmic heating. The use of high-intensity ultrasound helps preserve the bioactivity of the products. However, when sonication is performed at temperatures below 55 °C, it may not effectively inhibit microorganisms [75,76,77]. A summary of the technological processes used in the production of whey-based beverages is provided in Table 2.

In practice, both direct and indirect thermal treatments are used. A study by Kelleher et al. [78] investigated the impact of direct and indirect heat processing (preheating at 70 °C with final heating at 121 °C, and preheating at 80 °C with final heating at 135 °C, with a final hold time of 30 s and 2 s, respectively) on the properties of whey beverages. The beverages were made from 4%, 6%, and 8% (w/w) whey protein isolate (WPI). Significant differences were observed between the beverages treated with direct and indirect heating in terms of appearance and organoleptic properties. Beverages treated with direct heating contained less denatured protein, showed lower viscosity, and exhibited fewer changes in volatile compound profiles. Direct thermal treatment is particularly suitable for beverages with higher protein content.

Oliviera et al. [75] compared the effects of short-term thermal treatment and thermosonication on the properties of whey beverages. Beverages treated with thermosonication showed better microbiological quality and higher antioxidant, antihypertensive, and antidiabetic activities. Additionally, there was less degradation of ascorbic acid in the beverage. Whey beverages exhibited the features of better rheological properties and a better volatile compound profile compared to those treated with short-term thermal heating.

Ultrasound and thermosonication were compared to pasteurisation in a study by Jelicić et al. [79]. Both methods are considered non-thermal food processing techniques. During thermosonication with preheating to 55 °C, the best microbial inactivation of the whey-based beverage was achieved. Beverages treated with ultrasound and thermosonication exhibited better organoleptic properties compared to those treated with pasteurisation. Additionally, no sediment was observed in the beverages, and the colour remained unchanged throughout the experiment.

Barukčić et al. [80] also investigated the impact of high-intensity ultrasound on the properties of whey beverages. Thermosonication at 480 W for 10 min at 55 °C resulted in improved microbial and sensory properties of the drinks. On the other hand, ultrasound treatment led to an increase in the number of viable microorganisms during the activation process.

Table 2. Technological processes used in whey-based beverages manufacturing.

Technological Process	References
Direct and indirect heat processing	Kelleher et al. [78]
Thermosonication	Barukčić et al. [80] Oliviera et al. [75]
Ultrasound and thermosonication	Jeličić et al. [79]
High-intensity ultrasound	Herrera-Ponce et al. [81]
Supercritical carbon dioxide	luan Chen et al. [82] Yuk et al. [83] Ceni et al. [84] Amaral et al. [85]
Microfiltration	Castro-Muñoz et al. [86] Nazir et al. [87] Vieira et al. [88]

Table 2. Technological processes used in whey-based beverages manufacturing.

Technological Process	References
Direct and indirect heat processing	Kelleher et al. [78]
Thermosonication	Barukčić et al. [80] Oliviera et al. [75]
Ultrasound and thermosonication	Jeličić et al. [79]
High-intensity ultrasound	Herrera-Ponce et al. [81]
Supercritical carbon dioxide	luan Chen et al. [82] Yuk et al. [83] Ceni et al. [84] Amaral et al. [85]
Microfiltration	Castro-Muñoz et al. [86] Nazir et al. [87] Vieira et al. [88]

High-intensity ultrasound was also used to evaluate the antioxidant activity effect on fermentation and sensory properties of whey-based beverages in the study by Herrera-Ponce et al. [81]. The beverage subjected to ultrasound for 3 min contained the highest amount of L. casei 431 and showed the highest antioxidant capacity. Consumers rated the combination of 50% whey and 50% oat as the most suitable.

The use of supercritical carbon dioxide represents another advanced technology for beverage processing. This non-thermal and gentle method helps preserve the physicochemical, nutritional, and sensory properties of foods. Supercritical carbon dioxide processing has been applied successfully to the treatment of fruit juices. In contrast to pasteurisation methods, the use of supercritical carbon dioxide did not modify the physicochemical parameters (pH, soluble solids, titratable acidity, and bioactive components, including phenolics and anthocyanins) of whey beverages [82,83,84,85].

Lastly, it is essential to highlight the increasingly adopted microfiltration technology in the processing of milk and dairy products. This membrane filtration method utilises pressure to achieve separation. It offers several advantages, including reduced energy costs, highly efficient separation, ease of operation, and high productivity. During microfiltration, compounds with significant added value, such as carbohydrates, proteins, phenolic compounds, and pectin, are effectively separated. Additionally, in the dairy industry, microfiltration ensures bacterial reduction, enabling the production of milk with an extended shelf life [86,87,88]. Improper selection of the technological procedure for the production of whey-based beverages may adversely affect the technological properties of the whey beverage and, thus, its deterioration. Therefore, it is important to select an appropriate manufacturing process to maintain the quality of whey-based beverages [75].

6. Conclusions

Whey is a by-product of cheese or quark cheese or yoghurt production and is a liquid rich in protein, lactose, vitamins, and minerals. Above all, it has many health benefits due to its amino acid content. Previously, whey was used as part of livestock feed or mixed with wastewater and ended up in wastewater treatment plants. Nonetheless, this method of disposal is not suitable as it places a burden on the environment. However, the use of whey is still low, so producers try to incorporate whey in various forms into foodstuffs. A new product is unfermented or fermented whey beverages, which, due to their properties, are suitable for a wide range of consumers. Based on the review, it can be said that flavoured whey beverages are more prevalent among consumers. The addition of a flavouring ingredient increases acceptability in taste, aroma, and appearance. Fermented whey beverages exhibited a higher phenolic content, and the antioxidant activity of the beverages increased. New technological processes used in the production of whey beverages bring with them a number of positive features. Beverages treated with thermosonication, for example, contain more ascorbic acid, have a better microbial composition, and exhibit better organoleptic and rheological properties. Supercritical carbon dioxide, ultrasound, and microfiltration, among other techniques, were also applied. Processing whey for beverage production is, therefore, a suitable option that will increase the utilisation of whey and thus reduce the environmental impact of improper disposal.