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Article

Phytochemical and Functional Properties of Fruit and Vegetable Processing By-Products

by
Roberto Ciccoritti
1,*,
Roberto Ciorba
1,
Danilo Ceccarelli
1,
Monica Amoriello
2 and
Tiziana Amoriello
3,*
1
CREA—Research Centre for Olive, Fruit and Citrus Crops, Via di Fioranello 52, 00134 Rome, Italy
2
CREA—Central Administration, Via Archimede 59, 00197 Rome, Italy
3
CREA—Research Centre for Food and Nutrition, Via Ardeatina 546, 00178 Rome, Italy
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2024, 14(20), 9172; https://doi.org/10.3390/app14209172 (registering DOI)
Submission received: 10 September 2024 / Revised: 1 October 2024 / Accepted: 8 October 2024 / Published: 10 October 2024
(This article belongs to the Special Issue Application of Natural Components in Food Production)
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Abstract

:
Processing sustainability and the concept of zero waste discharge are of great interest for many industries. Every year, fruit and vegetable processing industries generate huge amounts of by-products, which are often intended for animal feed or discarded as waste, posing a problem to both environmental and economic points of view. However, to minimize the waste burden, the valorization of these residues received increased interest. In fact, fruit and vegetable by-products are an excellent source of valuable compounds, such as proteins, dietary fibers, lipids, minerals, vitamins, phenolic acids, flavonoids, anthocyanins, carotenoids, and pigments, which can be recovered and reused, creating new business prospects from a circular economy perspective. Understanding the chemical characteristics of these materials is a key concern for their valorization and the identification of their most appropriate intended use. In this study, the phytochemical and functional properties of fruit and vegetable processing by-products (peel and pomace) were investigated. Samples of different plants (i.e., apple, black and orange carrot, cucumber, kumquat, mango, parsnip, peach, black plum) were analyzed using chemical analytical methods and characterized using Fourier Transform Mid-Infrared spectroscopy (FT-MIR). The results highlighted their high nutritional composition in terms of protein, lipids, fiber, and ash, as well as bioactive and antioxidant profiles. These characteristics make these residues suitable as natural ingredients for the development of high-added-value products in food, cosmetic, and pharmaceutical industries.

1. Introduction

In recent decades, global food production and dietary patterns have undergone notable changes. Actual models of production, whilst they encourage growth, higher yields, and food security, are damaging the environment, increasing global greenhouse gas emissions, and driving biodiversity loss, water scarcity, the overuse of pesticides, nutrient pollution, climate change, and the excessive use of antibiotics [1,2,3,4,5]. Malnutrition is a widespread phenomenon in many areas of the planet. In fact, it is estimated that people from a lot of countries (77%) show a calorie deficit, 2 billion people exhibit a micronutrient deficiency, and an additional 2.2 billion people are considered overweight or obese [6]. Unhealthy, high-calory, and low-micronutrient diets, based on highly processed saturated fats and animal-based foods, increase the over-weight and obese global population [5]. Malnutrition can also cause diet-related non-communicable diseases [5].
In this context, the global food system cannot meet the food needs of 10 billion people by 2050 without impacts on water, land use, and gas emissions, and irreversibly damaging the planet. Agriculture accounts for 70% of freshwater consumption, the occupation of half the world’s habitable land, and 78% of the global eutrophication of oceans and freshwater [7]. Furthermore, 26.0% of anthropogenic greenhouse gas emissions are caused by agriculture and 14.5% by livestock production, especially beef and lamb [7]. Specifically, a comparison between plant food production and animal food production showed that, on average, producing animal protein (meat and dairy) requires 11 times more fossil fuel energy than grain-based protein [8]. For all these reasons, a transition to healthy, environmentally sustainable diets is necessary. The promotion of healthy and safe diets can be a starting point to guarantee food security, to provide sufficient affordable and nutritious foods, and to preserve biodiversity and the environment [9]. The Planetary Health Diet (PHD), based on the recommendations proposed by the EAT-Lancet Commission, can be considered a reference diet because it establishes scientific targets for healthy diets that will optimize human health. According to dietary requirements, personal preferences, and cultural traditions, healthy and sustainable diets encourage (1) an appropriate caloric intake, especially from fruits and vegetables, legumes, nuts, and whole grains; (2) low amounts of animal-sourced foods, such as red meat, and unsaturated rather than saturated fats; and (3) small amounts of refined grains, highly processed foods, and added sugars [5]. At the same time, the presence of adequate macronutrients and essential micronutrients in heathy diets must be ensured [10].
In recent years, an important ongoing field of research concerns the use of waste and by-products to provide healthy foods with a high content of nutrients and antioxidants and from plant-based resources, from the perspective of sustainability and circularity. According to the Food and Agriculture Organization (FAO), one-third of the global food production is lost or wasted along food supply chains. Food losses and waste have exponentially increased over the last few decades, with high negative effects on the environment and economic losses due to waste disposal [11,12]. Vegetables (24% of total losses and waste), fruits (22%), cereals (12%), oil crops (10%), potatoes (7%), and sugar beets (4%) constitute massive amounts of residues [12,13]. Specifically, it is estimated that the pre- and post-harvesting process and fruit and vegetable processing produce high amounts of by-products such as peels, seeds, shells, pods, pomace, etc., every year [14]. However, plant-based wastes or by-products can represent an excellent source of valuable and low-cost macronutrients, micronutrients, and functional compounds, such as protein, dietary fibers, polysaccharides, minerals, vitamins, polyphenols, essential oils, resins, flavor compounds, pigments, etc., and their valorization can ensure sustainability, circularity, and food security [15]. They can be used as functional ingredients for the formulation of new products with an enhanced nutritional profile (health-promoting properties) in food and beverage industries, as nutraceuticals in medicinal and pharmaceutical preparations, as a protein source in animal feed, as natural preservatives to maintain food quality, as agricultural compost, or as an inexpensive source of bioenergy (due to the high cellulose and lignin content) [16,17,18,19]. Phytochemical compounds in fruit and vegetable by-products, such as phenolic acids, flavonoids, anthocyanins, and carotenoids, received significant attention, mainly due to their possible benefits to human wellbeing. Several in vivo and in vitro studies demonstrated their antioxidant, antimicrobial, antidiabetic, anti-obesity, anti-inflammatory, and anti-carcinogenic properties [19,20,21,22,23,24,25,26,27].
In light of these considerations, our study aimed to investigate the potential of fruit and vegetable by-products, analyzing their functional and phytochemical properties, and their possible applications. To do this, the nutritional composition, the bioactive compounds and the antioxidant properties of some processing wastes (peel and pomace) of apple, black and orange carrot, cucumber, kumquat, mango, parsnip, peach, and black plum were analyzed using chemical analytical methods. Moreover, samples were characterized using Fourier Transform Mid-Infrared spectroscopy (FT-MIR) in order to highlight their molecular signatures.

2. Materials and Methods

2.1. Raw Materials and Experimental Design

Fruit and vegetable by-products (peel and pomace) were obtained by food processing. Samples belonged to apple (Malus domestica (Suckow) Borkh), black and orange carrot (Daucus carota L.), cucumber (Cucumis sativus L.), kumquat (Citrus japonica Thumb.), mango (Mangifera indica L.), parsnip (Pastinaca sativa L.), peach (Prunus persica (L.) Batsch), and black plum (Prunus domestica L.) by-products, which were considered in this study as shown in Table 1 and Figure 1. In order to compare the qualitative characteristics of all samples of by-products, they were processed in the laboratory in the following way. All samples were peeled, and the skin was separated from the pulp. The juices of apple, orange carrot, mango, peach, and black plum were extracted from the pulp using a juice extractor (mod. Pure Juice Pro, Kenwood Ltd., Havant, UK), which presses and squeezes the ingredients without damaging the nutrients thanks to the low rotation. The obtained pomaces were used for the analyses. All samples were stored at −20 °C in low-density polyethylene bags until use. An aliquot of each sample (300 g) was directly analyzed to determinate the centesimal composition, whereas 500 g of each sample was freeze-dried at −54 °C and 0.075 mbar for 72 h with an Edwards Modulyo 4K (UK) freeze dryer. Sample dehydration continued until 9% final moisture content was reached. Samples were finely milled (0.5 mm sieve) using a laboratory mill (Cyclotec, Tecator/Hoganas, Sweden) and kept protected from light and humidity until analysis. Freeze-dried samples were used to determine the bioactive compounds and antioxidant potential, and for Fourier Transform Mid-Infrared spectroscopy (FT-MIR) characterization. All analytical determinations were performed in triplicate.

2.2. Reagents Used to Perform the Analyses

Analytical reagent-grade hydrochloric acid, acetone, and methanol were obtained from VWR International S.r.l. (Milan, Italy). Standards of gallic acid, catechin, and Folin–Ciocalteu reagent were purchased from Sigma–Aldrich (Milan, Italy), as well as 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), sodium carbonate, vanillin, potassium persulfate, and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox). Deionized water was produced by a Milli-Q unit (Millipore, Bedford, MA, USA).

2.3. Proximate Analysis

The ICC standard methods 105/2, 136, and 104/1 were used to determined proteins (conversion factor 6.25), lipids, and ash, respectively [28]. Total dietary fiber (TDF) and soluble dietary fiber (SDF) contents were measured according to Lee et al. [29].

2.4. Determination of Bioactive Compounds and Antioxidant Capacity

Bioactive compounds (i.e., total phenolic content (TPC), total carotenoid content (TCC), total flavonoid content (FLC), chlorophyll a (Chl A), chlorophyll b (Chl B)) and antioxidant activity (AA) were performed on milled freeze-dried samples. Briefly, for TPC, FLC, and AA determination, each sample was homogenized with a blender (Ultra-Turrax T25, IKA Labortechnik, Staufen, Germany) in 25 mL of acidified (5 mM HCl) methanol/water solution (70/30 v/v) and subsequently sprinkled in a thermostatic bath at 37 °C for 2 h. The mixture was then submitted to an ultrasound-assisted extraction for another 30 min (40 kHz, 10 °C). The resulting extracts were centrifuged (centrifuge mod. 4239R, ALC International, Milan, Italy) at 6792 rpm for 15 min at 4 °C. Pellets were extracted once again in the same way. Then, the supernatants were collected and immediately analyzed according to Amoriello et al. [30] and Lolletti et al. [31]. The Folin–Ciocalteu method was applied for TPC determination, and the results are expressed in mg of gallic acid equivalent of dry weight (mg GAE 100 g−1 dw). Briefly, 0.4 mL of extract were added to 16.0 mL water, 2.0 mL of Folin–Ciocalteu phenol reagent, and 6.0 mL of 1 M sodium carbonate, and the final volume was adjusted to 25 mL with the same solution used for the extraction. Samples were read at 760 nm after 2 h using an Evolution 300 UV-Vis Spectrophotometer (Thermo Electron Scientific Instruments, Madison, WI, USA). Determination of GAE was performed by GA standard curve (0.025–0.500 mg mL−1).
Vanillin assay method was applied to FLC determination. FLC was obtained from a calibration curve, using catechin as a standard, and the results were expressed as milligram of catechin equivalents per 100 g of dry weight (mg CAE 100 g−1 dw). Briefly, a volume of 3 mL of 4% (w/v) vanillin in methanol and 0.5 mL of a known dilution of the extract were added to a test tube. After 3–5 min, 1.5 mL of concentrated HCl was added to the solution, mixed, and incubated for 15 min at 20 °C. The absorbance was read at 500 nm using a UV-Vis Spectrophotometer. A blank was prepared by substituting the vanillin solution in the reaction mix with methanol. Determination of CAE was performed by CA standard curve (0.025–0.500 mg mL−1).
Pigments, i.e., chlorophyll a (Chl A), chlorophyll b (Chl B), and carotenoids (TCC), were determined using acetone as a solvent. Briefly, aliquots of 0.5 g of freeze-dried samples were extracted with 8 mL of iced acetone (−20 °C) containing 0.01% butylated hydroxytoluene (BHT; 0.5 mg mL−1) as an antioxidant. To avoid degradation and isomerization of carotenoids, amber glassware was used, and sample preparation was performed under dim light conditions. The extraction was performed at room temperature for 1 h under continuous stirring (300 rpm). Then, the extract was filtered through Whatman No 1 paper (Sigma-Aldrich; Milan, Italy). The residue was extracted once again in the same way. Then, the filtrates were combined together and immediately analyzed. The supernatant was separated and the absorbances were read at 400–700 nm on the Evolution 300 UV-Vis Spectrophotometer. It was recorded that chlorophyll a showed the maximum absorbance at 662 nm, chlorophyll b at 646 nm, and total carotene at 470 nm. The amount of these pigments was calculated as follows.
Chl A = 11.75 A662 − 2.350 A645
Chl B = 18.61 A645 − 3.960 A662
TCC = 1000 A470 − 2.270 Chl A − 81.4 Chl B/227
The results were expressed as micrograms of chlorophyll a, chlorophyll b, and β carotene equivalent per grams of dry weight (μg g−1 ChlAE dw, μg g−1 ChlBE dw, μg g−1 βCE dw, respectively).
The antioxidant activity evaluation of the extracts was performed with 2,2-diphenyl-1-picrylhydrazyl (DPPH). Briefly, 1.5 mL of DPPH solution was added to 1.5 mL of the extract and, after 15 min, absorbance at 515 nm was determined using the UV-Vis Spectrophotometer. The percent inhibition activity of extract was calculated as follows:
[(A0 − A1)/A0] × 100
where A0 was the absorbance of the control and A1 was the absorbance of the extract. Trolox (0.5–10 μg mL−1) was used as the reference compound and AA was expressed as μg of Trolox equivalent (TE) mg−1 dw.

2.5. FT-MIR Analysis

MIR spectra were collected at room temperature with an FTIR-ATR spectrometer (iS 10 FT-IR Nicolet Thermo Fisher Scientific Inc., Waltham, MA USA) equipped with a diamond crystal cell (ATR), as described by Amoriello et al. [32]. The spectra were acquired at 4 cm−1 resolution with 32 scans of each milled sample and an interval between spectra data points of 0.482 cm−1 CO2 atmospheric correction in the wavenumber range of 4000–650 cm−1. A background spectrum of air was collected to correct the sample spectra. After scanning each sample, the ATR crystal was cleaned with propan-2-ol and ethanol and the cleanliness of the ATR crystal was verified. Measurements were repeated 10 times and spectra were processed with the OMNIC™ software version 2016 (Thermo Fisher Scientific Inc., USA).

2.6. Statistical Analysis

Statistical differences in all measured variables were assessed using the Kruskal–Wallis non-parametric test and Dunn’s post hoc test at a significance level of 5% using PAST statistical software (version 4.02, [33]).

3. Results

3.1. Nutritional Composition

The nutritional composition in terms of the ash, protein, lipid, total dietary fiber (TDF), and soluble dietary fiber (SDF) contents of different fruit and vegetable by-products is shown in Table 1.
The ash content statistically differed between samples, showing the highest mean value for cucumber peel (9.6 ± 0.1 g 100 g−1 dw), followed by orange carrot peel (8.7 ± 0.3 g 100 g−1 dw), while the lowest mean value was for apple pomace (1.5 ± 0.1 g 100 g−1 dw). Similar results were found by Sai Prasanna and Mitra [34], Chantaro et al. [35], Clementez et al. [36], and De la Peña-Armada [37]. Almost all the samples showed similar values of protein content, from the 4.8 ± 0.1 g 100 g−1 dw of apple pomace to the 8.1 ± 0.3 g 100 g−1 dw of the peels of parsnip and peach. The exceptions were the apple peel and cucumber peel samples, with protein values equal to 0.7 ± 0.1 g 100 g−1 dw and 20.5 ± 0.2 g 100 g−1 dw, respectively. Similar characteristics were noted by Sai Prasanna and Mitra [34] and Li et al. [38]. The lipid content of all samples is quite low, ranging between the 0.5 ± 0.1 g 100 g−1 dw of peach pomace and the 5.5 ± 0.1 g 100 g−1 dw of apple pomace, similar to the results of Rudke et al. [39] and De la Peña-Armada [37]. Fruits and vegetables can be considered as an important source of fiber. Our study confirmed this: apple peel and pomace, black and orange carrot peel, cucumber peel, kumquat peel and pomace, and peach peel and pomace showed a fiber value greater than 50.0 g 100 g−1 dw. On the contrary, mango had a low fiber content (4.3 ± 0.5 g 100 g−1 dw for pomace and 15.1 ± 0.8 g 100 g−1 dw for peel), in accordance with Marçal et al. [40] and Hasan et al. [41]. TDF can be classified into two types of complementary fibers: soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). The quantity of SDF in peels was higher than in pomaces for apple, orange carrot, and mango samples. An opposite behavior was observed for peach and black plum samples.

3.2. Bioactive Compounds and Antioxidant Capacity

Vegetable and fruit by-products were compared for their bioactive compound content in terms of soluble phenolic content (TPC), flavonoids (FLC), carotenoids (TCC), chlorophyll a (Chl A), and chlorophyll b (Chl B), and their antioxidant activity (AA). The statistically significant differences of the phytochemical profile (p < 0.05) are shown in Table 2.
Phenolic compounds are biologically active plant metabolites involving phenols with one or more hydroxyl groups, and they are effective in neutralizing free radicals [41]. Moreover, they can exhibit anticancer, antimicrobial, and antimutagenic properties [42]. However, the bioaccessibility and the bioavailability of phenolic compounds strongly depend on the microstructure of fruits and vegetables. Higher benefits for human health can be obtained in free-form macromolecules, rather than in conjugated form [43]. In our study, TPC content ranged from the 1934 ± 124 mg 100 g−1 GAE dw of black carrot peel and the 1915 ± 43 mg 100 g−1 dw of mango peel to the 8 ± 1 mg 100 g−1 GAE dw of orange carrot peel. A considerable amount of TPC was also found in samples of black plum peel (1576 ± 33 mg 100 g−1 GAE dw) and apple peel (1228 ± 25 mg 100 g−1 GAE dw). Generally, fruit and vegetable peels show a high level of phenolic compounds, especially for root vegetables [44]. However, phenolic accumulation can depend on species, varieties, climatic conditions, vegetative stage, and agronomic management [45].
Flavonoids are a class of polyphenolic secondary metabolites found in plants, characterized by the ability to scavenge free radicals. They can protect against cardiovascular diseases and certain cancers [41]. Apple peel and black plum peel showed the highest values of flavonoid content (2434 ± 124 mg 100 g−1 CAE dw and 2396 ± 75 mg 100 g−1 CAE dw, respectively), whereas the orange carrot pomace and parsnip showed the lowest (6 ± 0 mg 100 g−1 CAE dw and 5 ± 0 mg 100 g−1 CAE dw, respectively). In general, vegetable and fruit peels are rich source of flavonoids; however, industrial processing could have a negative impact on FLC, strongly reducing it, especially if subjected to high temperatures [46].
Fruit and vegetable by-products provide a wide range of natural bioactive pigments (secondary metabolites), including carotenoids and chlorophylls. These pigments can be used as natural colorants in food and beverages preparations, as dietary supplements and pharmaceuticals, or as antioxidants with positive effects on human health [47]. Carotenoids are a fat-soluble group of pigments which can vary from yellow to orange and red. They can be associated with several beneficial effects, such as the reduction in the risk of cardiovascular diseases, cancer, neurovegetative diseases, macular degeneration, diabetes, and liver diseases [48,49,50]. Chlorophylls are oil-soluble pigments with a green color, and they can have two different structures: chlorophyll a, with a methyl (-CH3) group at the 7-carbon position and a blue-green color, and chlorophyll b, with an aldehyde (-CHO) group at the 7-carbon position and a blue-yellow color [51]. Chlorophylls a and b can exhibit strong antioxidant, anti-inflammatory, and antimutagenic properties [52]. In the present study, the total carotenoid content ranged from the 5.8 ± 0.9 μg g−1 βCE dw of parsnip peel to the 753.2 ± 3.1 μg g−1 βCE dw of orange carrot peel. The highest value of chlorophyll a was found for cucumber peel (21.50 ± 0.30 μg g−1 ChlAE dw), followed by black carrot peel (3.80 ± 0.20 μg g−1 ChlAE dw), whilst the lowest was for black plum pomace (0.13 ± 0.03 μg g−1 ChlAE dw) and parsnip peel (0.11 ± 0.04 μg g−1 ChlAE dw). Regarding chlorophyll b, cucumber peel showed the highest value (12.30 ± 0.70 μg g−1 ChlBE dw), whereas black plum pomace (0.18 ± 0.03 μg g−1 ChlBE dw) and parsnip peel (0.17 ± 0.06 μg g−1 ChlBE dw) showed the lowest values. These results for cucumber peel were already highlighted by Zeyada et al. [53], and those for pigments by Sharma et al. [54].
As described above, fruits and vegetables can have a high antioxidant content which can contribute to human health due to the protection they offer from diseases. There are a lot of different classes and types of antioxidants in plant foods. The total antioxidant capacity (AA) is frequently used to assess the antioxidant status of biological samples and the cumulative capacity of food components to scavenge free radicals. Mango peel was the sample with the greatest antioxidant capacity (5.64 ± 0.01 μg mg−1 TE dw), followed by apple peel (4.95 ± 0.02 μg mg−1 TE dw), whereas orange carrot pomace, cucumber peel, and parsnip peel exhibited 0.14 ± 0.01 μg mg−1 TE dw, 0.33 ± 0.05 μg mg−1 TE dw, and 0.36 ± 0.1 μg mg−1 TE dw, respectively. These differences could be due to the ability of the DPPH radical chemical characteristics to react with the phenolic lipid class [55]. Our results highlighted that almost all the samples had a high total antioxidant capacity. It was mainly due to the high total phenolic content for black carrot, mango, black plum, and apple peels and black plum pomace; to the high total flavonoid content for apple peel and black plum peels and pomaces; to the high total carotenoid content for orange carrot and kumquat peels and pomaces; and to the high chlorophyll a and b content for cucumber and black carrot peels, in accordance with previous studies [39,41,56,57,58,59,60]. However, the phytochemical composition of the considered fruit and vegetable by-products could depend on many factors, such as the soil composition, abiotic and biotic stresses, sun exposure, the stage of ripening, and post-harvest handling [61].

3.3. FT-MIR Spectral Characterization of Samples

FT-MIR spectroscopy was used to investigate the characteristic functional groups of the powdered peel and pomace samples. FT-MIR spectrum of samples from 4000 to 650 cm−1 revealed similar profiles, with some differences in peak intensities (Figure 2). Characteristic absorption peaks in relation to the different samples (from 13 to 19), which revealed a different chemical composition, are evidenced in Figure 2 and Table 3.
As expected from the composition of by-products, the main absorbance bands can be attributed to proteins, sugars and carbohydrates, and crude fiber components, as described by Schulz and Baranska [62].
The peak at around 3288 cm−1 could be assigned to the OH and NH stretching vibrations and was found in all samples because these functional groups could be ascribed by polysaccharide (especially hemicellulose and cellulose) or protein and polyphenol N-H stretch amide [62]. The highest peak intensity was observed in cucumber peel (about 58% transmittance), followed by kumquat sample (about 62% transmittance) and peach peel (65% transmittance), while the lowest was characteristic of black carrot, plum, and parsnip peels (about 83%, 72%, and 70%, respectively).
A peak at around 2924 cm−1 was found in all samples and could be attributed to the CH and CH2 stretching vibrations of galacturonic acid methyl esters, characteristic of the hydrocarbonated skeleton of the saccharide. According to Aslam et al. [63], the spectral regions between 2800 and 3000 cm−1, typical of CH2 stretching, could be associated with lipid and carbohydrate. The signal intensities for this region also reflected the sample profiles observed at 3288 cm−1: cucumber and parsnip peels showed the maximum and minimum signals, respectively. The peak at 2849 cm−1 is associated with the presence of carbohydrates and it was found only for mango peel, apple peel, and black plum peel. The peak at around 2898 cm−1 is associated with the –CH stretching vibrations, CH3 symmetric stretching, and CH2 symmetric stretching of carbohydrates. The signal at around 1740 cm−1, found in all samples, can be attributed to the C=O stretching vibration of the carboxylic acid methyl ester of the pectin [64]. Luca et al. [65] attributed this peak to beta carotene, and it is characteristic of samples with a high content of carotenoids.
Differences in peak intensities among fruit and vegetable samples were observed at 1740 cm−1: the signal was high for fruit by-products (black plum, mango, and apple peels) and low for vegetables (carrots, parsnip, and cucumber), suggesting a strong relationship with dietary fiber (pectins).
The spectral band centered at about 1620 cm−1 was in all samples and it was assigned to the C=O stretching vibration of free carboxyl groups (lignin, benzene ring, pectin, and protein), the C=C stretch of the aromatic ring, and from the superimposition of the H–O–H bending of the amid I and C–N stretching of proteins [64]. The signals at 1620 cm−1 were higher in vegetable samples than fruit samples, probably due to the different protein content. The spectral region between 1491 and 1200 cm−1 of all samples was characterized by three main peaks, respectively, at 1404, 1372, and 1253 cm−1. The first two peaks (1404 and 1372 cm−1) could be assigned to the C–O and CH3 stretching of the carboxylic group related to organic acids and sugars, while the signal at 1253 cm−1 could refer to the C–O in hydroxybenzene, the bending vibration absorption peak of C–O in the benzene ring, and to the C=C stretch aromatic characteristic of polyphenols, as reported by Bureau et al. [66] and Ruiz et al. [67]. A high variability of signal intensity was observed among samples, highlighting the maximum intensity (value lower than 75%) for cucumber peel and the minimum in parsnip peel (value lower than 85%), in accordance with the chemical determination of total phenols (Table 2).
The spectral bands between 1199 and 1000 cm−1 allowed us to identify specific band profiles, which are typical for the different hydroxyl-aromatic molecules that constitute the phenolic compounds (i.e., tannins) and alkanes that are the bons of polysaccharides (i.e., cellulose), as observed by Park et al. [68]. The peaks near 1100 cm−1 and 1030 cm−1 were assigned to C–O stretching (aromatic ring phenols) and C–C stretching (cellulose). The first peak was found in all samples except for cucumber and black plum peels, whereas the second peak was not found only in the black plum peel sample.
The spectral bands between 1000 and 750 cm−1 were characterized by six prominent peaks at 988, 922, 892, 868, 829, and 776 cm−1, which are typical of polysaccharides (such as pectins) and phenolic compounds (such as carotenoids), in accordance with Luca et al. [65]. Differently from the other samples, the black plum peel sample only showed a peak at 892 cm−1, whereas the cucumber sample only showed a peak at 776 cm−1.
For each species, the differences in peak intensities and FT-MIR profiles for all samples were low.

3.4. Valorization Approaches for Fruit and Vegetable By-Products

Fruit and vegetable by-products can be an excellent source of health-promoting bioactive compounds, including proteins, fibers, sugars, minerals, vitamins, essential oils, polyphenols, phenolic acids, flavonoids, pigments, etc., which can be recovered, valorized, and commercialized from a circular and sustainable perspective. The recoverable fractions of these residues represent a huge amount of waste generated during the processing stages, and they can vary between 20% and 33% for peels, and 15% and 32% for pomaces, of the initial weight of the fruit or vegetable (data measured from the samples of this study). However, it is important to correctly characterize these wastes from a chemical point of view to identify the best use for their valorization. At the same time, the procedures and technologies for the extraction of these molecules can affect the sustainability of the processes. Traditional extraction methods can be expensive and time-, energy-, and harmful-solvent-consuming. Moreover, bioactive compounds are sensitive to high temperatures and prolonged extraction times. On the contrary, greener and non-conventional methods, such as supercritical fluid extraction, pressurized liquid extraction, microwave-assisted extraction, ultrasound-assisted extraction, pulse electric field extraction, and enzyme-assisted extraction, can be eco- and user-friendly, use few or no solvents, and have short extraction times [47,52].
Most of the by-products considered in this study can be reintegrated in food and beverage industries or as animal feed to enhance their technological, sensorial, and nutritional properties. For example, apple, carrot, mango, and citrus pomaces and peels or their extracts can be used as ingredients for bakery products (bread, cakes, muffins, biscuits), dairy products (yogurt and ice-cream), meat products (patties and nuggets of chicken, buffalo, mutton); the apple pomace can be used in jams or extruded snacks and beverages; the carrot pomace and mango peel can be used in pasta; the citrus wastes and mango peel can be used in jellies, jams, and probiotic drinks [57,69,70,71]. The introduction of these by-products could be due to the high soluble and insoluble fiber contents (in particular, cellulose, hemicellulose, lignin, pectin, etc.), which increase the technological properties of products due to their effects on binding flavor components, swelling capacity, water holding capacity, fermentability, gel formation, and increasing viscosity [72]. Dietary fibers, in particular, the soluble fractions, also have positive effects on human health, with benefits for the gastrointestinal system, lipid and glucose metabolism, and reducing the levels of serum triglycerides and hepatic cholesterol [71,72,73].
The functional properties of dietary fibers (water permeability, gelling, and network formation) combined with the biological antimicrobial and antioxidative activity of phenols make possible the use of these by-products in the development of food packaging, including edible films [57,61,74]. In fact, their incorporation can reduce food oxidation and, therefore, food spoilage, extending food shelf life through protection against biological, physical, and chemical deterioration [57,75].
Fruit and vegetable by-products also provide a wide range of natural phenols and pigments such as chlorophylls, carotenoids, anthocyanins, betanin, etc. They can be used in the food industry as natural colorants, as ingredients in functional foods, as food additives, or to increase food safety and sensory attributes; in cosmetics as ingredients in soaps, perfumes, creams, skincare products, mouthwashes, body lotions, etc.; and in pharmaceutics as a component with anti-disease effects, including anti-hepatotoxicity, anti-hyperlipidemia, anti-inflammation, anti-hypertension, anti-cancer, anti-depression, and anti-hypoglycemia, due to its antioxidant properties [46,51,52,75,76,77]. For example, Amaya-Cruz et al. [78] highlighted that the juice by-products of mango and peach are rich in dietary fiber, carotenoids, and polyphenols, and they can be used to prevent hepatic steatosis and hyperglycaemia. Macagnan et al. [73] emphasized that apple pomace can have a positive effect on decreasing the levels of serum triglycerides and hepatic cholesterol due to high dietary fiber and bioactive compounds. Uthpala et al. [79] showed that the high fiber content of cucumber peel can help to reduce constipation and to prevent colon cancer. Kenari et al. [80] reported the beneficial effect of parsnip constituents on human health due to their anti-inflammatory properties and the prevention of the angiogenesis of cancer tissue.
As mentioned so far, fruit and vegetable processing waste can be a valuable source of renewable biomass useful for the biotechnological production of chemicals applied in a wide variety of industries. Understanding the heterogeneity and the chemical characteristics of food by-products is crucial in developing effective valorization strategies. However, the heterogeneous composition of the by-products and their perishable nature, due to their high water content, which can generate rapid microbial spoilage and harmful odor gases, can represent a limit to the industrial exploitation of these materials because this can make it difficult to store them for processing and extracting bioactive compounds. These by-products should be processed quickly or dried, but in both cases problems could arise. Drying involves an additional energy cost, making the valorization process less sustainable and less economically attractive. Therefore, highly energy efficient and economically sustainable drying methods should be applied. Moreover, their rapid processing is strictly connected to logistics. It would be necessary to locate valorization facilities near the food industries to reduce waste transportation costs, thereby fostering a circular system, as pointed out by Peydayesh [81]. These aspects are crucial for industry acceptance. The adoption of practices for the recovering and up-cycling of these by-products can lead to economic opportunities, favoring virtuous paths for local development. This can be achieved only through close cooperation between researchers, entrepreneurs, industrialists, and policymakers. At the same time, educational initiatives to enhance consumers’ knowledge and appreciation are required on the recovery and reuse of by-products because the willingness of consumers to accept new foods or new products from fruit and vegetable waste is considered low [12].

4. Conclusions

In this study, the nutritional and phytochemical composition and the molecular structure of fruit and vegetable by-products (peel and pomace) were investigated. These residues of food processing are valuable sources rich in proteins (0.7–20.5 g 100 g−1 dw), fibers (4–68 g 100 g−1 dw), and phytochemicals with a high antioxidant capacity, including phenols (8–1934 mg 100 g−1 GAE dw), flavonoids (5–2434 mg 100 g−1 CAE dw), carotenoids (6–753 μg g−1 βCE dw), and pigments (Chl A: 0.1–21.5 μg g−1 ChlAE dw; Chl B: 0.2–12.3 μg g−1 ChlBE dw) which are associated with health-promoting properties. The FT-MIR spectral profiles showed the molecular signatures of all samples, highlighting the differences in absorption peaks and in their intensities associated with specific chemical functional groups. The most promising strategies to recover these residues can be to convert them into powders and to reuse them to develop food, animal feed, cosmetic, and pharmaceutical applications, enhancing the nutritional or functional properties of the value-added products, contributing to the companies’ profit. The exploitation of these underestimated biomasses represents an opportunity from a zero-waste perspective and can also have environmental and economic advantages for many industries.

Author Contributions

Conceptualization, T.A. and R.C. (Roberto Ciccoritti); methodology, T.A. and R.C. (Roberto Ciccoritti); validation, T.A., R.C. (Roberto Ciccoritti) and D.C.; formal analysis, T.A., R.C. (Roberto Ciorba) and R.C. (Roberto Ciccoritti); investigation, T.A., R.C. (Roberto Ciccoritti) and D.C.; data curation, T.A., R.C. (Roberto Ciccoritti) and M.A.; writing—original draft preparation, T.A. and R.C. (Roberto Ciccoritti); writing—review and editing, T.A., R.C. (Roberto Ciccoritti), R.C. (Roberto Ciorba), D.C. and M.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article; further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Springmann, M.; Godfray, H.C.; Rayner, M.; Scarborough, P. Analysis and valuation of the health and climate change cobenefits of dietary change. Proc. Natl. Acad. Sci. USA 2016, 113, 4146–4151. [Google Scholar] [CrossRef] [PubMed]
  2. Steffen, W.; Richardson, K.; Rockström, J.; Cornell, S.E.; Fetzer, I.; Bennett, E.M.; Biggs, R.; Carpenter, S.R.; De Vries, W.; De Wit, C.A.; et al. Planetary boundaries: Guiding human development on a changing planet. Science 2015, 347, 1259855. [Google Scholar] [CrossRef] [PubMed]
  3. Tilman, D.; Clark, M. Global diets link environmental sustainability and human health. Nature 2014, 515, 518–522. [Google Scholar] [CrossRef] [PubMed]
  4. Whitmee, S.; Haines, A.; Beyrer, C.; Boltz, F.; Capon, A.G.; de Souza Dias, B.F.; Ezeh, A.; Frumkin, H.; Gong, P.; Head, P.; et al. Safeguarding human health in the Anthropocene epoch: Report of The Rockefeller Foundation-Lancet Commission on planetary health. Lancet 2015, 386, 1973–2028. [Google Scholar] [CrossRef]
  5. Willett, W.; Rockström, J.; Loken, B.; Springmann, M.; Lang, T.; Vermeulen, S.; Garnett, T.; Tilman, D.; DeClerck, F.; Wood, A.; et al. Food in the Anthropocene: The EAT–Lancet Commission on healthy diets from sustainable food systems. Lancet 2019, 393, 447–492. [Google Scholar] [CrossRef]
  6. Navarre, N.; Schrama, M.; de Vos, C.; Mogollon, J.M. Interventions for sourcing EAT-Lancet diets within national agricultural areas: A global analysis. One Earth 2023, 6, 31–40. [Google Scholar] [CrossRef]
  7. Aureli, V.; Nardi, A.; Palmieri, N.; Peluso, D.; Di Veroli, J.N.; Scognamiglio, U.; Rossi, L. Sustainability Perception of Italian Consumers: Is it Possible to Replace Meat, and What Is the Best Alternative? Nutrients 2023, 15, 3861. [Google Scholar] [CrossRef]
  8. Pimentel, D.; Pimentel, M. Sustainability of meat-based and plant-based diets and the environment. Am. J. Clin. Nutr. 2003, 78 (Suppl. 3), S660–S663. [Google Scholar] [CrossRef]
  9. Food and Agriculture Organization of the United Nations (FAO). Sustainable Healthy Diets: Guiding Principles; World Health Organization: Rome, Italy, 2019; ISBN 978-92-5-131875-1. [Google Scholar]
  10. Beal, T.; Ortenzi, F.; Fanzo, J. Estimated micronutrient shortfalls of the EAT–Lancet planetary health diet. Lancet Planet Health 2023, 7, e233–e237. [Google Scholar] [CrossRef]
  11. Amicarelli, V.; Bux, C. Food waste measurement toward a fair, healthy and environmental-friendly food system: A critical review. Br. Food J. 2020, 123, 2907–2935. [Google Scholar] [CrossRef]
  12. De Boni, A.; Ottomano Palmisano, G.; De Angelis, M.; Minervini, F. Challenges for a Sustainable Food Supply Chain: A Review on Food Losses and Waste. Sustainability 2022, 14, 16764. [Google Scholar] [CrossRef]
  13. Caldeira, C.; De Laurentiis, V.; Corrado, S.; van Holsteijn, F.; Sala, S. Quantification of food waste per product group along the food supply chain in the European Union: A mass flow analysis. Resour. Conserv. Recycl. 2019, 149, 479–488. [Google Scholar] [CrossRef] [PubMed]
  14. Food and Agriculture Organization of the United Nations (FAO). The State of Food and Agriculture 2019, Moving forward on Food Loss and Waste Reduction, Rome, Italy, 2019. Available online: http://www.fao.org/3/ca6030en/ca6030en.pdf (accessed on 27 August 2024).
  15. Maric, M.; Grassino, A.N.; Zhu, Z.; Barba, F.J.; Brncic, M.; Rimac Brncic, S. An overview of the traditional and innovative approaches for pectin extraction from plant food wastes and by-products: Ultrasound-, microwaves-, and enzyme-assisted extraction. Trends Food Sci. Technol. 2018, 76, 28–37. [Google Scholar] [CrossRef]
  16. Nardella, S.; Conte, A.; Del Nobile, M.A. State-of-Art on the Recycling of By-Products from Fruits and Vegetables of Mediterranean Countries to Prolong Food Shelf Life. Foods 2022, 11, 665. [Google Scholar] [CrossRef]
  17. Osorio, L.L.D.R.; Flórez-López, E.; Grande-Tovar, C.D. The potential of selected agri-food loss and waste to contribute to a circular economy: Applications in the food, cosmetic and pharmaceutical industries. Molecules 2021, 26, 515. [Google Scholar] [CrossRef] [PubMed]
  18. Dahiya, S.; Kumar, A.N.; Sravan, J.S.; Chatterjee, S.; Sarkar, O.; Mohan, S.V. Food waste biorefinery: Sustainable strategy for circular bioeconomy. Bioresour. Technol. 2018, 248, 2–12. [Google Scholar] [CrossRef]
  19. Banerjee, J.; Singh, R.; Vijayaraghavan, R.; MacFarlane, D.; Patti, A.F.; Arora, A. Bioactives from fruit processing wastes: Green approaches to valuable chemicals. Food Chem. 2017, 225, 10–22. [Google Scholar] [CrossRef]
  20. Shahidi, F.; Ambigaipalan, P. Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects–a review. J. Funct. Foods 2015, 18, 820–897. [Google Scholar]
  21. Kumar, K.; Kumar, S. Role of nutraceuticals in health and disease prevention: A review. South Asian J. Food Technol. Environ. 2015, 1, 116–121. [Google Scholar] [CrossRef]
  22. Bordiga, M.; Travaglia, F.; Locatelli, M. Valorisation of grape pomace: An approach that is increasingly reaching its maturity—A review. Int. J. Food Sci. Technol. 2019, 54, 933–942. [Google Scholar] [CrossRef]
  23. Coman, V.; Teleky, B.E.; Mitrea, L.; Martău, G.A.; Szabo, K.; Călinoiu, L.F.; Vodnar, D.C. Bioactive potential of fruit and vegetable wastes. Adv. Food Nutr. Res. 2020, 91, 157–225. [Google Scholar] [PubMed]
  24. Galali, Y.; Omar, Z.A.; Sajadi, S.M. Biologically active components in by-products of food processing. Food Sci. Nutr. 2020, 8, 3004–3022. [Google Scholar] [CrossRef] [PubMed]
  25. Mwaurah, P.W.; Kumar, S.; Kumar, N.; Panghal, A.; Attkan, A.K.; Singh, V.K.; Garg, M.K. Physicochemical characteristics, bioactive compounds and industrial applications of mango kernel and its products: A review. Compr. Rev. Food Sci. Food Saf. 2020, 19, 2421–2446. [Google Scholar] [CrossRef] [PubMed]
  26. Villacís-Chiriboga, J.; Elst, K.; Van Camp, J.; Vera, E.; Ruales, J. Valorization of byproducts from tropical fruits: Extraction methodologies, applications, environmental, and economic assessment: A review (Part 1: General overview of the byproducts, traditional biorefinery practices, and possible applications). Compr. Rev. Food Sci. Food Saf. 2020, 19, 405–447. [Google Scholar] [CrossRef]
  27. Bansal, A.; Priyadarsini, C. Medicinal Properties of Phytochemicals and Their Production. In Natural Drugs from Plants; El-Shemy, H.A., Ed.; IntechOpen: London, UK, 2021. [Google Scholar]
  28. International Association for Cereal Science and Technology. ICC Standard Methods (Methods No. 104/1, 105/2, 136); ICC: Vienna, Austria, 2003. [Google Scholar]
  29. Lee, S.C.; Prosky, L.; DeVries, J.W. Determination of total, soluble, and insoluble, dietary fibre in foods enzymatic-gravimetric method, MES-TRIS buffer: Collaborative study. J. Assoc. Off. Anal. Chem. 1992, 75, 395–416. [Google Scholar]
  30. Amoriello, T.; Mellara, F.; Amoriello, M.; Ceccarelli, D.; Ciccoritti, R. Powdered seaweeds as a valuable ingredient for functional breads. Eur. Food Res. Technol. 2021, 247, 2431–2443. [Google Scholar] [CrossRef]
  31. Lolletti, D.; Principio, L.; Ciorba, R.; Mitrano, F.; Ceccarelli, D.; Antonucci, F.; Manganiello, R.; Ciccoritti, R. Asimina triloba: Crop years, cultivars and ripening time influence on qualitative parameters. Sci. Hortic. 2021, 289, 110481. [Google Scholar] [CrossRef]
  32. Amoriello, T.; Ciccoritti, R.; Carbone, K. Vibrational spectroscopy as a green technology for predicting nutraceutical properties and antiradical potential of early-to-late apricot genotypes. Postharvest Biol. Technol. 2019, 155, 156–166. [Google Scholar] [CrossRef]
  33. Hammer, Ø.; Harper, D.A.; Ryan, P.D. PAST: Paleontological statistics software package for education and data analysis. Palaeontol. Electron. 2001, 4, 9. [Google Scholar]
  34. Sai Prasanna, N.; Mitra, J. Isolation and characterization of cellulose nanocrystals from Cucumis sativus peels. Carbohydr. Polym. 2020, 247, 116706. [Google Scholar] [CrossRef]
  35. Chantaro, P.; Devahastin, S.; Chiewchan, N. Production of antioxidant high dietary fiber powder from carrot peels. LWT—Food Sci. Technol. 2008, 41, 1987–1994. [Google Scholar] [CrossRef]
  36. Clementz, A.; Torresi, P.A.; Molli, J.S.; Cardell, D.; Mammarella, E.; Yori, J.C. Novel method for valorization of by-products from carrot discards. LWT—Food Sci. Technol. 2019, 100, 374–380. [Google Scholar] [CrossRef]
  37. De la Peña-Armada, R.; Mateos-Aparicio, I. Sustainable Approaches Using Green Technologies for Apple By-Product Valorisation as A New Perspective into the History of the Apple. Molecules 2022, 27, 6937. [Google Scholar] [CrossRef] [PubMed]
  38. Li, J.; Ye, F.; Zhou, Y.; Lei, L.; Chen, J.; Li, S.; Zha, G. Tailoring the composition, antioxidant activity, and prebiotic potential of apple peel by Aspergillus oryzae fermentation. Food Chem. X 2024, 21, 101134. [Google Scholar] [CrossRef] [PubMed]
  39. Rudke, C.R.M.; Zielinski, A.A.F.; Ferreira, S.R.S. From Biorefinery to Food Product Design: Peach (Prunus persica) By-Products Deserve Attention. Food Bioprocess Tech. 2023, 16, 1197–1215. [Google Scholar] [CrossRef]
  40. Marçal, S.; Sousa, S.; Araújo-Rodrigues, H.; Silva, I.V.; Campos, D.A.; Pintado, M. Impact of washing and freezing on nutritional composition, bioactive compounds, antioxidant activity and microstructure of mango peels. Food Chem. 2024, 442, 138368. [Google Scholar] [CrossRef]
  41. Hasan, M.M.; Islam, M.R.; Haque, A.R.; Kabir, M.R.; Kamrul Hasan, S.M. Fortification of bread with mango peel and pulp as a source of bioactive compounds: A comparison with plain bread. Food Chem. Adv. 2024, 5, 100783. [Google Scholar] [CrossRef]
  42. Guan, R.; Van Le, Q.; Yang, H.; Zhang, D.; Gu, H.; Yang, H.; Sonne, C.; Lam, S.S.; Zhong, J.; Jianguang, Z.; et al. A review of dietary phytochemicals and their relation to oxidative stress and human diseases. Chemosphere 2021, 271, 129499. [Google Scholar] [CrossRef]
  43. Arias, A.; Feijoo, G.; Moreira, M.T. Exploring the potential of antioxidants from fruits and vegetables and strategies for their recovery. Innov. Food Sci. Emerg. Technol. 2022, 77, 102974. [Google Scholar] [CrossRef]
  44. Farahnaky, A.; Kamali, E.; Golmakani, M.T.; Gavahian, M.; Mesbahi, G.; Majzoobi, M. Effect of ohmic and microwave cooking on some bioactive compounds of kohlrabi, turnip, potato, and radish. J. Food Meas. Charact. 2018, 12, 2561–2569. [Google Scholar] [CrossRef]
  45. Bors, M.D.; Semeniuc, C.A.; Socaci, S.; Varva, L.; Moldovan, O.; Vlaic, R. Total phenolic content and antioxidant capacity of radish as influenced by the variety and vegetative stage. Bull. UASVM Food Sci. Technol. 2015, 72, 77–81. [Google Scholar]
  46. Bashir, R.; Tabassum, S.; Rashid, A.; Rehman, S.; Adnan, A.; Ghaffar, R. Bioactive components of root vegetables. In Advances in Root Vegetables Research; Kaushik, P., Ed.; IntechOpen: London, UK, 2022. [Google Scholar]
  47. Sharma, M.; Usmani, Z.; Gupta, V.K.; Bhat, R. Valorization of fruits and vegetable wastes and by-products to produce natural pigments. Crit. Rev. Biotechnol. 2021, 41, 535–563. [Google Scholar] [CrossRef] [PubMed]
  48. Eggersdorfer, M.; Wyss, A. Carotenoids in human nutrition and health. Arch. Biochem. Biophys. 2018, 652, 18–26. [Google Scholar] [CrossRef] [PubMed]
  49. Saini, R.K.; Prasad, P.; Lokesh, V.; Shang, X.; Shin, J.; Keum, Y.-S.; Lee, J.-H. Carotenoids: Dietary Sources, Extraction, Encapsulation, Bioavailability, and Health Benefits—A Review of Recent Advancements. Antioxidants 2022, 11, 795. [Google Scholar] [CrossRef]
  50. Sanna, D.; Fadda, A. Waste from Food and Agro-Food Industries as Pigment Sources: Recovery Techniques, Stability and Food Applications. Nutraceuticals 2022, 2, 365–383. [Google Scholar] [CrossRef]
  51. Carrillo, C.; Nieto, G.; Martínez-Zamora, L.; Ros, G.; Kamiloglu, S.; Munekata, P.E.S.; Pateiro, M.; Lorenzo, J.M.; Fernández-López, J.; Viuda-Martos, M.; et al. Novel Approaches for the Recovery of Natural Pigments with Potential Health Effects. J. Agric. Food Chem. 2022, 70, 6864–6883. [Google Scholar] [CrossRef]
  52. Benucci, I.; Lombardelli, C.; Mazzocchi, C.; Esti, M. Natural colorants from vegetable food waste: Recovery, regulatory aspects, and stability—A review. Compr. Rev. Food Sci. Food Saf. 2022, 21, 2715–2737. [Google Scholar] [CrossRef]
  53. Zeyada, N.N.; Zeitoun, M.A.M.; Barbary, O.M. Utilization of Some Vegetables and Fruits Waste As Natural Antioxidants. Alex. J. Fd. Sci. Technol. 2008, 5, 1–11. [Google Scholar]
  54. Villaño, D.; Fernández-Pachón, M.S.; Moyá, M.L.; Troncoso, A.M.; García-Parrilla, M.C. Radical scavenging ability of polyphenolic compounds towards DPPH free radical. Talanta 2007, 71, 230–235. [Google Scholar] [CrossRef]
  55. Villamil-Galindo, E.; Piagentini, A.M. Sequential ultrasound-assisted extraction of pectin and phenolic compounds for the valorisation of ‘Granny Smith’ apple peel. Food Biosci. 2022, 49, 101958. [Google Scholar] [CrossRef]
  56. Asma, U.; Morozova, K.; Ferrentino, G.; Scampicchio, M. Apples and Apple By-Products: Antioxidant Properties and Food Applications. Antioxidants 2023, 12, 1456. [Google Scholar] [CrossRef] [PubMed]
  57. Sucheta; Misra, N.N.; Yadav, S.K. Extraction of pectin from black carrot pomace using intermittent microwave, ultrasound and conventional heating: Kinetics, characterization and process economics. Food Hydrocoll. 2020, 102, 105592. [Google Scholar] [CrossRef]
  58. Moulick, S.P.; Jahan, F.; Islam, M.B.; Hasan, M.S.; Islam, M.J.; Ahmed, S.; Karmakar, D.; Ahmed, F.; Saha, T.; Sandhani Dey, S.; et al. Nutritional characteristics and antiradical activity of turmeric (Curcuma longa L.), beetroot (Beta vulgaris L.), and carrot (Daucus carota L.) grown in Bangladesh. Heliyon 2023, 9, e21495. [Google Scholar] [CrossRef] [PubMed]
  59. Lou, S.N.; Ho, C.T. Phenolic compounds and biological activities of small-size citrus: Kumquat and calamondin. J. Food Drug Anal. 2017, 25, 162–175. [Google Scholar] [CrossRef] [PubMed]
  60. Marçal, S.; Pintado, M. Mango peels as food ingredient / additive: Nutritional value, processing, safety and applications. Trends Food Sci. Technol. 2021, 114, 472–489. [Google Scholar] [CrossRef]
  61. Schulz, H.; Baranska, M. Fruits and vegetables. In Infrared Spectroscopy for Food Quality Analysis and Control; Sun, D.-W., Ed.; Elsevier Inc.: Amsterdam, The Netherlands, 2008; pp. 321–353. [Google Scholar]
  62. Aslam, A.; Ranjan, R.K.; Dass, A. Pattern of spatial variability in granulometric and mineralogical characteristics across an ecologically sensitive sub-tropical wetland (Bihar, India). Int. J. Sediment Res. 2023, 38, 516–529. [Google Scholar] [CrossRef]
  63. Reale, S.; Biancolillo, A.; Foschi, M.; Di Donato, F.; Di Censo, E.; D’Archivio, A.A. Geographical discrimination of Italian carrot (Daucus carota L.) varieties: A comparison between ATR FT-IR fingerprinting and HS-SPME/GC-MS volatile profiling. Food Control 2023, 146, 109508. [Google Scholar] [CrossRef]
  64. Luca, M.I.; Ungureanu-Iuga, M.; Mironeasa, S. Carrot Pomace Characterization for Application in Cereal-Based Products. Appl. Sci. 2022, 12, 7989. [Google Scholar] [CrossRef]
  65. Bureau, S.; Ruiz, D.; Reich, M.; Gouble, B.; Bertrand, D.; Audergon, J.M.; Renard, C.M. Application of ATR-FTIR for a rapid and simultaneous determination of sugars and organic acids in apricot fruit. Food Chem. 2009, 115, 1133–1140. [Google Scholar] [CrossRef]
  66. Ruiz, D.; Reich, M.; Bureau, S.; Renard, C.M.; Audergon, J.M. Application of reflectance colorimeter measurements and infrared spectroscopy methods to rapid and nondestructive evaluation of carotenoids content in apricot (Prunus armeniaca L.). J. Agric. Food Chem. 2008, 56, 4916–4922. [Google Scholar] [CrossRef]
  67. Park, Y.S.; Im, M.H.; Ham, K.S.; Kang, S.G.; Park, Y.; Namiesnik, J.; Leontowicz, H.; Leontowicz, M.; Trakhtenberg, S.; Gorinstein, S. Quantitative assessment of the main antioxidant compounds, antioxidant activities and FTIR spectra from commonly consumed fruits, compared to standard kiwi fruit. LWT-Food Sci. Technol. 2015, 63, 346–352. [Google Scholar] [CrossRef]
  68. Sharma, M.; Sridhar, K.; Gupta, V.K.; Dikkala, P.K. Greener technologies in agri-food wastes valorization for plant pigments: Step towards circular economy. Curr. Res. Green Sustain. Chem. 2022, 5, 100340. [Google Scholar] [CrossRef]
  69. Eliopoulos, C.; Markou, G.; Langousi, I.; Arapoglou, D. Reintegration of Food Industry By-Products: Potential Applications. Foods 2022, 11, 3743. [Google Scholar] [CrossRef] [PubMed]
  70. Suri, S.; Singh, A.; Nema, P.K. Current applications of citrus fruit processing waste: A scientific outlook. Appl. Food Res. 2022, 2, 100050. [Google Scholar] [CrossRef]
  71. Tariq, A.; Sahar, A.; Usman, M.; Sameen, A.; Azhar, M.; Tahir, R.; Younas, R.; Khan, M.I. Extraction of dietary fiber and polyphenols from mango peel and its therapeutic potential to improve gut health. Food Biosci. 2023, 53, 102669. [Google Scholar] [CrossRef]
  72. Ratu, R.N.; Velescu, I.D.; Stoica, F.; Usturoi, A.; Arsenoaia, V.N.; Crivei, I.C.; Postolache, A.N.; Lipsa, F.D.; Filipov, F.; Florea, A.M.; et al. Application of Agri-Food By-Products in the Food Industry. Agriculture 2023, 13, 1559. [Google Scholar] [CrossRef]
  73. Macagnan, F.T.; dos Santos, L.R.; Sampaio Roberto, B.; de Moura, F.A.; Bizzani, M.; da Silva, L.P. Biological properties of apple pomace, orange bagasse and passion fruit peel as alternative sources of dietary fibre. Bioact. Carbohydr. Diet. Fibre 2015, 6, 1–6. [Google Scholar] [CrossRef]
  74. Salgado, P.R.; Ortiz, C.M.; Musso, Y.S.; Di Giorgio, L.; Mauri, A.N. Edible films and coatings containing bioactives. Curr. Opin. Food Sci. 2015, 5, 86–92. [Google Scholar] [CrossRef]
  75. Soares Mateus, A.R.; Pena, A.; Sendón, R.; Almeida, C.; Almeida Nieto, G.; Khwaldia, K.; Sanches Silva, A. By-products of dates, cherries, plums and artichokes: A source of valuable bioactive compounds. Trends Food Sci. Technol. 2023, 131, 220–243. [Google Scholar] [CrossRef]
  76. Ebrahimi, P.; Shokramraji, Z.; Tavakkoli, S.; Mihaylova, D.; Lante, A. Chlorophylls as Natural Bioactive Compounds Existing in Food By-Products: A Critical Review. Plants 2023, 12, 1533. [Google Scholar] [CrossRef]
  77. Aktar, S.; Rauf, A.; Imran, M.; Qamar, M.; Riaz, M.; Mubarak, M.S. Black carrot (Daucus carota L.), dietary and health promoting perspectives of its polyphenols: A review. Trends Food Sci. Technol. 2017, 66, 36–47. [Google Scholar] [CrossRef]
  78. Amaya-Cruz, D.M.; Rodríguez-González, S.; Pérez-Ramírez, I.F.; Loarca-Piña, G.; Amaya-Llano, S.; Gallegos-Corona, M.A.; Reynoso-Camacho, R. Juice by-products as a source of dietary fibre and antioxidants and their effect on hepatic steatosis. J. Funct. Foods 2015, 17, 93–102. [Google Scholar] [CrossRef]
  79. Uthpala, T.G.G.; Marapana, R.A.U.J.; Lakmini, K.P.C.; Wwttimuny, D.C. Nutritional bioactive compounds and health benefits of fresh and processed cucumber (Cucumis sativus L.). Sumerianz J. Biotechnol. 2020, 3, 75–82. [Google Scholar]
  80. Kenari, H.M.; Kordafshari, G.; Moghimi, M.; Eghbalian, F.; TaherKhani, D. Review of pharmacological properties and chemical constituents of Pastinaca sativa. J. Pharmacopunct. 2021, 24, 14–23. [Google Scholar] [CrossRef] [PubMed]
  81. Peydayesh, M. Sustainable Materials via the Assembly of Biopolymeric Nanobuilding Blocks Valorized from Agri-Food Waste. Sustainability 2024, 16, 1286. [Google Scholar] [CrossRef]
Applsci 14 09172 g001
Figure 1. Fruits and vegetables considered in this study.
Figure 1. Fruits and vegetables considered in this study.
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Applsci 14 09172 g002aApplsci 14 09172 g002bApplsci 14 09172 g002cApplsci 14 09172 g002dApplsci 14 09172 g002e
Figure 2. Raw FT-MIR spectra ((A) apple peel; (B) apple pomace; (C) orange carrot peel; (D) orange carrot pomace; (E) black carrot peel; (F) cucumber peel; (G) kumquat peel and pomace; (H) parsnip peel; (I) mango peel; (J) mango pomace; (K) peach peel; (L) peach pomace; (M) black plum peel; (N) black plum pomace).
Figure 2. Raw FT-MIR spectra ((A) apple peel; (B) apple pomace; (C) orange carrot peel; (D) orange carrot pomace; (E) black carrot peel; (F) cucumber peel; (G) kumquat peel and pomace; (H) parsnip peel; (I) mango peel; (J) mango pomace; (K) peach peel; (L) peach pomace; (M) black plum peel; (N) black plum pomace).
Applsci 14 09172 g002aApplsci 14 09172 g002bApplsci 14 09172 g002cApplsci 14 09172 g002dApplsci 14 09172 g002e
Table 1. Nutritional composition (ash, protein, lipids, total dietary fiber TDF, and soluble dietary fiber SDF) of fruit and vegetable by-products. Differences between letters in the same column indicate significant differences (p < 0.05).
Table 1. Nutritional composition (ash, protein, lipids, total dietary fiber TDF, and soluble dietary fiber SDF) of fruit and vegetable by-products. Differences between letters in the same column indicate significant differences (p < 0.05).
Ash
(g 100 g−1 dw)		Protein
(g 100 g−1 dw)		Lipids
(g 100 g−1 dw)		TDF
(g 100 g−1 dw)		SDF
(g 100 g−1 dw)
Applepeel2.1 ± 0.1 i0.7 ± 0.1 f0.8 ± 0.1 e60.1 ± 1.0 b20.4 ± 0.9 b
pomace1.5 ± 0.1 j4.8 ± 0.3 e5.5 ± 0.1 a67.7 ± 0.9 a16.5 ± 0.8 c
Black carrotpeel6.1 ± 0.2 d7.5 ± 0.2 c1.2 ± 0.1 d49.5 ± 0.9 c13.4 ± 0.6 d
Orange carrotpeel8.7 ± 0.3 b7.9 ± 0.2 bc1.3 ± 0.1 d50.3 ± 0.7 c10.6 ± 0.4 e
pomace4.9 ± 0.1 e7.1 ± 0.2 c1.2 ± 0.1 d27.5 ± 0.8 f5.9 ± 0.4 g
Cucumberpeel9.6 ± 0.1 a20.5 ± 0.2 a1.5 ± 0.2 cd58.3 ± 1.0 b26.2 ± 0.6 a
Kumquatpeel and pomace2.4 ± 0.1 h7.6 ± 0.2 c2.9 ± 0.2 b61.5 ± 1.0 b12.6 ± 0.7 d
Mangopeel2.9 ± 0.3 g5.8 ± 0.5 d3.2 ± 0.2 b15.1 ± 0.8 g4.8 ± 0.6 gh
pomace1.9 ± 0.2 i6.4 ± 0.3 d1.2 ± 0.1 d4.3 ± 0.5 h1.8 ± 0.3 i
Parsnippeel7.5 ± 0.3 c8.1 ± 0.3 b1.8 ± 0.2 c38.2 ± 1.5 d7.6 ± 0.6 f
Peachpeel4.5 ± 0.2 f8.1 ± 0.3 b1.6 ± 0.1 c51.3 ± 0.8 c10.8 ± 0.6 e
pomace4.1 ± 0.2 f7.5 ± 0.3 c0.5 ± 0.1 f61.2 ± 0.9 b20.5 ± 0.7 b
Black plumpeel3.1 ± 0.2 g7.9 ± 0.2 bc2.5 ± 0.3 b27.6 ± 1.0 f3.6 ± 0.4 h
pomace2.9 ± 0.2 g7.3 ± 0.2 c1.7 ± 0.1 c30.8 ± 1.1 e5.8 ± 0.5 g
Table 2. Bioactive compounds (TPC: total phenolic content, FLC: total flavonoid content, TCC: total carotenoid content, Chl A: chlorophyll a, Chl B: chlorophyll b) and antioxidant capacity (AA) of fruit and vegetable by-products. Differences between letters in the same column indicate significant differences (p < 0.05).
Table 2. Bioactive compounds (TPC: total phenolic content, FLC: total flavonoid content, TCC: total carotenoid content, Chl A: chlorophyll a, Chl B: chlorophyll b) and antioxidant capacity (AA) of fruit and vegetable by-products. Differences between letters in the same column indicate significant differences (p < 0.05).
TPC
(mg 100 g−1 GAE dw)		FLC
(mg 100 g−1 CAE dw)		TCC
(μg g−1 βCE dw)		Chl A
(μg g−1 ChlAE dw)		Chl B
(μg g−1 ChlBE dw)		AA
(μg mg−1 TE dw)
Applepeel1228 ± 25 c2434 ± 124 a48.2 ± 2.4 g0.40 ± 0.10 fg0.50 ± 0.10 f4.95 ± 0.02 b
pomace47 ± 5 j79 ± 2 g23.9 ± 1.3 h0.55 ± 0.05 f0.88 ± 0.05 e0.73 ± 0.04 h
Black carrotpeel1934 ± 124 a466 ± 16 c194.1 ± 3.8 d3.80 ± 0.2 b6.30 ± 0.10 b2.64 ± 0.09 e
Orange carrotpeel495 ± 23 k20 ± 1 h753.2 ± 3.1 a0.51 ± 0.06 f0.80 ± 0.10 e3.31 ± 0.34 d
pomace8 ± 1 b6 ± 0 j436.3 ± 2.7 b1.37 ± 0.04 d2.20 ± 0.10 c0.14 ± 0.01 j
Cucumberpeel168 ± 12 h25 ± 1 h7.1 ± 0.1 i21.50 ± 0.30 a12.30 ± 0.70 a0.33 ± 0.05 i
Kumquatpeel and pomace561 ± 40 e13 ± 1 i348.3 ± 7.0 c0.31 ± 0.10 gh0.50 ± 0.10 f3.26 ± 0.11 d
Mangopeel1915 ± 43 a166 ± 9 f91.7 ± 2.4 e2.10 ± 0.10 c1.30 ± 0.10 d5.64 ± 0.01 a
pomace366 ± 7 f65 ± 3 g65.0 ± 3.9 f0.22 ± 0.04 h0.33 ± 0.80 g2.38 ± 0.11 f
Parsnippeel117 ± 14 i5 ± 0 j5.8 ± 0.9 j0.11 ± 0.04 i0.17 ± 0.06 h0.36 ± 0.01i
Peachpeel400 ± 38 f394 ± 6 d92.1 ± 3.4 e0.38 ± 0.04 g0.55 ± 0.04 f2.25 ± 0.05 f
pomace246 ± 8 g363 ± 4 e68.6 ± 1.6 f0.38 ± 0.08 g0.51 ± 0.10 f1.77 ± 0.05 g
Black plumpeel1576 ± 33 b2396 ± 75 a50.9 ± 7.0 g1.00 ± 0.30 e0.50 ± 0.30 f3.17 ± 0.13 d
pomace938 ± 4 d1518 ± 22 b22.6 ± 1.7 h0.13 ± 0.03 i0.18 ± 0.03 h4.30 ± 0.05 c
Table 3. Spectral features of peel and pomace samples (A = apple peel; B = apple pomace; C = orange carrot peel; D = orange carrot pomace; E = black carrot peel; F = cucumber peel; G = kumquat peel and pomace; H = parsnip peel; I = mango peel; J = mango pomace; K = peach peel; L = peach pomace; M = black plum peel; N = black plum pomace).
Table 3. Spectral features of peel and pomace samples (A = apple peel; B = apple pomace; C = orange carrot peel; D = orange carrot pomace; E = black carrot peel; F = cucumber peel; G = kumquat peel and pomace; H = parsnip peel; I = mango peel; J = mango pomace; K = peach peel; L = peach pomace; M = black plum peel; N = black plum pomace).
Main Peak
(cm−1)		Wave Number Range (cm−1)SamplesTypical Band
32883655–3000A; B; C; D; E; F; G; H; I; J; K; L; M; NO–H stretching vibrations
H-bonded hydroxyl of polysaccharide (especially hemicellulose and cellulose) or polyphenols
N–H stretch amide
29242990–2800A; B; C; D; E; F; G; H; I; J; K; L; M; NC–H1, C–H2, and C–H3 symmetric stretches of hydro carbonated skeleton of polysaccharide and carbohydrates
2849A; B; M; J; M; N
17431800–1701A; B; C; D; E; F; G H; I; J; K; L; M; NC=O stretching vibration of the carboxylic acid methyl ester (i.e., pectins)
16201700–1500A; B; C; D; E; F; G; H; I; J; K; L; M; NC=O stretching vibration of free carboxyl groups (pectin and protein)
C=C stretch aromatic (phenols)
1404
1372
1253		1499–1200A; B; C; D; E; H; F; G; I; J; K; L; M; NC–H2 bending (xyloglucan, cellulose)
C=C stretch aromatic (phenols)
C–H3 groups C–O stretching (sugars)
11001199–1001A; B; C; D; E; F; G; H; I; J; K; LC–O stretching (aromatic ring phenols),
C–C stretching (cellulose)
1030A; B; C; D; E; F; G; H; I; J; K; L; M; N
9881000–750A; B; C; D; E; G; H; I; J; K; LC–O bending (pectins),
C=C stretch (aromatic ring)
C–H bending of benzene ring of phenols
922
868
829		A; B; C; D; E; G; H; I; J; K; L; M; N
892M; N
776A; B; F; G; I; J; M; N
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MDPI and ACS Style

Ciccoritti, R.; Ciorba, R.; Ceccarelli, D.; Amoriello, M.; Amoriello, T. Phytochemical and Functional Properties of Fruit and Vegetable Processing By-Products. Appl. Sci. 2024, 14, 9172. https://doi.org/10.3390/app14209172

AMA Style

Ciccoritti R, Ciorba R, Ceccarelli D, Amoriello M, Amoriello T. Phytochemical and Functional Properties of Fruit and Vegetable Processing By-Products. Applied Sciences. 2024; 14(20):9172. https://doi.org/10.3390/app14209172

Chicago/Turabian Style

Ciccoritti, Roberto, Roberto Ciorba, Danilo Ceccarelli, Monica Amoriello, and Tiziana Amoriello. 2024. "Phytochemical and Functional Properties of Fruit and Vegetable Processing By-Products" Applied Sciences 14, no. 20: 9172. https://doi.org/10.3390/app14209172

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