Recently, there has been an on-growing interest in adding fruit and vegetable waste in food for improvement of its sensory characteristics, health properties and increasing of bioactive compounds.
Fruit and vegetable waste have been used in the production of functional foods for their nutraceutical properties (Majerska et al., 2019). There are many new functional food products containing fruit and vegetable waste on the market and their production is increasing every day (Majerska et al.,2019; Kowalska et al., 2017; Donno et al.,2018). For example, functional food has been successfully produced from star fruit residues. Shui et al., (2006) have come to conclusion that residue power can be used for the production of functional food, which manifests health properties due to the high content of polyphenols and antioxidant of star fruit residues.
Fruit and vegetable waste has also been used as natural food additives, it was observed that artificial additives which have been used in the food industries up until recently with the aim of preserving freshness, nutritive quality, flavour and colour of food, are toxic, especially in high doses. Hence interest for natural food additives has been increasing (Wadhwa & Bakshi 2013; Schilderman et al., 1995). Certain extracts from FV waste, such as anthocyanins from eggplant, anthoxanthins from potato peels, aarotenoids from tomato peels, lycopene from tomato byproducts have been used as potential natural food colorants in the modern food industry (Faustino et al., 2019; Kaur et al., 2011; Rizk et al., 2014; De Ancos et al., 2015, Chaitanya Lakshmi, 2014). In addition, agro-food byproducts, especially fruit peels and seeds have been used as preservatives, anti-oxidants, texturizing agents, emulsifiers, bulking agents, firming agents, etc. (Faustino et al., 2019),
Fruit and vegetable wastes has been also utilized in the production of juices, (Laufenberg et al., 2003); jellies (Madhav & Pushpalatha, 2006), and jams (Singh et al., 2009) or for their enrichment.
In addition, fruit waste and extracts from fruit waste have been added in the production of herbal and fruit teas, for example, oils obtained from sweet and bitter oranges have been used for tea formulations (Wadhwa & Bakshi, 2013; Majerska et al, 2019).
FVW has also been used for making of alcoholic beverages. Apple pomace has been used for the production of cider (Wadhwa & Bakshi 2013; Kou, 2019; Way et al., 2019). Certain fruit waste such as Black currant, bilberry, chokeberry and grape pomace have been successfully utilized in making of wine (Majerska et al., 2019). Apple and grape pomace have been added to the wine with the aim of enhancing its taste (Majerska et al., 2019). Guerrero et al. (2013) came to conclusion that dietary fibre from grape and apple pomace is capable of absorbing tannins which are responsible for tart taste of short aging wine (Guerrero, et al., 2013).
The potential of apples, grapes, oranges wastes have been explored for making of brandy (Wadhwa & Bakshi,2013; Verma et al., 2000). In addition apple pomace has been used for producing of beer (Verma et al., 2000). Wastes from pineapple and orange peel and certain vegetable waste have been utilized for vinegar production. (Gautam & Guleria, 2007; Wadhwa & Bakshi,2013, Aye, 2016; Chakraborty et al., 2018).
Fruit and vegetable waste have found to be useful either as FVW flour, or by being used as food additives. For example: Sudha et al.(2015) studied the use of mango peel or pulp fibre in the preparation of cake and other bakery products. It has been determined that this waste is fibre rich ingredient and that it improves the nutritional qualities of the products.
Some of the fruit and vegetable waste is proven to have a positive impact on dairy products (de Souza de Azevedo et al., 2018; Majerska et al., 2019). Lucera et al.,(2018) established that adding of flour obtained from red and white grape pomace, broccoli tomato peel, artichokes, and corn bran by-products, made cheese more firm and increased its total phenolic and flavonoid content compared to the control samples where no fruit and vegetable waste was added.
Another example is incorporation of dietary fibre extracted from stone pear, celery root, celery leaves, spinach and oranges into the production of butter. Addition of dietary fibre extracts from fruit and vegetable made butter more firm, easily spreadable and extended its shell life (Saraç et al., 2016).
The number of lactose intolerant people has recently been increasing. Dairy products are probiotic foods. Besides showing positive effects on dairy products, FVW can also be used as their replacement for production of products for people who are lactose intolerant. Certain fruit waste are reported to be probiotic food cariers due to the high content of vitamins, mineral, antioxidants and the absence of dairy allergens (Majerska et al., 2019).For example, Vodnar et al., (2019) did a study of using bioactive compounds from agro-industrial waste for production of probiotic juices.
Fruit and vegetable waste has also been used for improvement of meat products. For example, Fernández- López et al., (2008), added orange fibre to dry fermented sausage. The fibre obtained from orange did not impact flavour and it promoted the growth of necessary microflora and resulted in the decrease of nitrite. It also extended its shell-life (O’Shea et al., 2012). Viuda-Martos et al. (2010) did a following study and established that adding of orange fibre reduced the growth of pathogens in the sausage and retarded the oxidation, extending its possible utilization (O’Shea et al., 2012). Apple and fresh plum pomace has also been successfully added to meat products increasing its antioxidant capacity, nutritional value and extending its shelf-life (Henriquez et al., 2010; Lorenzo et al, 2017, O’Shea et al., 2012). The addition of certain FVW such as grape seed, broccoli powder or green tea extracts prolonged the shelf-life of chicken meat by inhibiting lipid oxidation (Banerjee et al., 2012; Pateiro et al., 2014, Majerska et al., 2019).
In the study conducted by Sanchez-Alonso (2010), addition of grape pomace dietary fibre to fish, enhanced its health and sensory properties, improved its water retention capacity and retarded lipid oxidation (Sanchez-Alonso et al., 2007). The meat has also showed enhancement after FVW addition.
Overall, it is clear that there is a huge variety of successful ways in which fruit and vegetable wastes, by products and their extracts can be incorporated into food for human consumption. FVW improves food’s nutritional quality, sensory characteristics and enhances its health properties as well.
Fruit and vegetable wastes represent a highly underexploited resource of valuable bioactive compounds and phytonutrients. Bioactive compounds represent primary and secondary metabolites of plants (Banerjee et al., 2017) They include dietary fibers, polyphenols, pigments, enzymes, sugar derivatives, vitamins, minerals and oils (Sagar et al., 2018). These compounds and nutrientsmay be used in a wide range of different industries. Some of them have proven health effects which includeantimicrobial, anticancer, antiviral, antimutagenic, antioxidant and cardioprotective activities (Banerjee et al., 2017; Dilas et al., 2009; Yahia et al., 2017; Sagar et al., 2018). In addition, they have proven useful in food, cosmetics, pharmaceutical, paper and textile industries (Galanakis, 2012; Laufenberg, et al. 2003, Banerjee et al., 2017; Sagar et al., 2018).
The process of extraction is being constantly improved by the application of novel technologies (Herrero et al., 2010; Sagar et al., 2018). These novel technologies and their modifications are introduced into the methodology with the aim of maximizing the yield and rate of the target compounds, clearing the compounds from toxic substances and impurities, providing grade nature of the final product and avoiding any functionality loss during processing (Galanakis, 2012).
Dietary fibre represent biomolecules, impervious to digestion by gastrointestinal enzymes and they include cellulose, hemicellulose, pectic substances, beta glucans, resistant dextrin, inulin, gums, chitosan oligosaccaharides, lignin, etc. (Mudgil, 2017;). Based on their water solubility, dietary fibre can be soluble and insoluble (Dhingra et al., 2012).
Recently there has been a lot of interest in FVW lignocellulosic biomass as well as renewable sources of bioactive polysaccharides. This is due to newly found approaches for valorisation of cellulose, hemicellulose and lignin. The utilization of cellulose has extended to biomedical section: for medical diagnostics and cancer screenings (Ratajczak & Stobiecka, 2019). It has also been used as pharmaceutical excipient (Domínguez et al., 2019). It is often used as diluent or filler in solid oral dosage formulations. (Credou & Berthelot, 2014; Banerjee et al., 2017).
In biomedical applications its use is established for hydrogels, including drug delivery, wound dressings and tissue engineering scaffolds, bioimaging, wearable sensors (Du et al., 2019; Fu et al., 2019). In addition, cellulose is frequently used in the food industries, and for the extraction of phenolic compounds from grape pomace (Drider et al., 1994; Meyer et al., 1998; Sagar et al., 2018). For its production, following fruit and waste is often used: mango peels (Saravanan et al., 2012; Wadhwa &Bakshi, 2013), banana waste (Elanthikkal et al., 2010); potato peel (dos Santos et al., 2012; Sagar et al., 2018); mandarin peel (Hiasa et al., 2014), etc.
Pectin, successfully extracted from number of fruit and vegetable waste has been used in food industry; pharmaceutics as gelling agent, thickener (Liu et al., 2003; Rabbani et al., 2001; Banerjee et al., 2017), and recently for biomedical applications for drug delivery, gene delivery, wound healing and tissue engineering (Munarin et al., 2012).
Resistant starch, obtained from fruit waste such as banana peel, jackfruit seeds, durian waste and mango kernel, like hemicelluloses, can only be digested in colon and its fermentation results in many health benefits too (Fuentes-Zaragoza, et al., 2010; Ho et al., 2019; Banerjee et al., 2017).
Fruit and vegeteable waste represents a good source of proteins as well. Their content is especially high in seeds (Banerjee et al., 2017). Apart from fruit and vegetable seeds, banana peels (Amini Khoozani et al., 2019); pea straws (Wadhwa & Bakshi, 2013), potato peels, avocado waste; (Chitturi et al., 2013) cabbage leaves; carrot pomace, apple pomace, green pea peels, mango peel, pineapple peel, tomato solid waste, pea pods, organe peel, cauliflower leave, etc. have a good amount of proteins too (Sharma et al., 2016; Sagar et al., 2018). Certain fruit and vegetable waste have more than 20% of crude protein which is why they are used as ruminant feed. These include, cabbage leaves, bottle gourd pulp, potato vines, radish leaves sugar beet leaves, snow peas. (Bakshi et al., 2016).
Apart from contributing to nutritional value of animal feed, certain proteins exibit health beneficial activities which is why they are extracted from fruit and vegetable waste. For example, kiwifruit seed has been used for the extraction of actinidin. This enzyme is responsible for digestion of proteins in small intestines. Due to its probiotic activities, it is commonly added to dairy products. (Puglisi et al., 2012, Boland, 2013).
Enzymes are also widely utilized and their contribution is high and varies in many industries. For example, amylases are abundantly used in food industries for the production of fruit juices, cheese, chocolate cakes and syrups (Laufenberg et al., 2009; Sagar et al., 2018; Toumi et al., 2016: Saini et al., 2017). They are also used in pharmaceutical, brewing and textile industries too (Saini et al., 2017).
The most common fruit and vegetable wastes used for the production of amylases are: bananapeel (Oshoma et al., 2019), orange peel (Uygut & Tanyildizi, 2018); potato peels (Pereira et al., 2017); date waste(Acoureneet al., 2014; Sagar et al., 2018), rice bran, wheat bran (Almanaa et al., 2019); and mango kernels (Kumar et al., 2013; Sagar et al., 2018).
Invertase is used for the production of invert sugar, artificial sweeteners, chocolates, lactic acid, glycerol, candies and confectionary (Veana et al., 2018; Aehlew, 2004; Sagar et al., 2018; Mashetty, & Biradar, 2019). The production of this enzyme using fruit and vegetable waste demands also the presence of sucrose, lactose and fructose. (Sagar et al., 2018). It is also used for production of pharmaceutical products and extension of shell life of products. (Kumar &Kesavapillai, 2012; Panda et al., 2016; Sagar et al., 2018;)
Pectinase is commonly used in food industries in making of wine and fruit juices (Nighojkar et al., 2019; New et al., 2018). It is also applied for extraction of pigments (Munde et al., 2017), and essential oils from fruit and vegetable wastes (Castilho et al., 2000; Sagar et al., 2018 ).In addition, it plays a rolein production of good quality paper (Ahlawat et al., 2008; Rebello et al., 2017), for fermentation of coffee and tea and treatment of pectic waste (Kashyap et al. 2001; Rebello et al., 2017). Citrus waste peel (Ahmed et al., 2016); banana peel (Sethi et al., 2016); apple peel (Chauhan et al., 2019); sugarcane bagasse (Biz et al., 2016.), pineapple stem (Kavuthodi, & Sebastian,2018), have been used for the production of pectinases.
Fruit and vegetable waste are also rich in lipids– oils. For example: the orange peels (Boukroufa et al., 2015), fennel waste (Cautela et al., 2018); apple and pear seed (Yukui, 2009); mango seed (Sultana, 2019); apricot seeds (Stryjecka et al.,2019); tomato seeds (Giuffrè, 2017);lemon peel (Ciriminna et al., 2017), represent a good source of oil. FVW oil contributes to inhibition of breast cancer proliferation (Ayoub et al., 2017). Certain oils such as lemon oil manifest strong cytotoxicity towards skin cancer, gastric cancer, and brain cancer cell line (Manjunath, et al., 2020). Garlic and onion oil for example exibit anti-obesity properties and hypolipidemic effects (Yang et al., 2018). It also shows antioxidant, anti-inflammatory, antibacterial, antiviral and antifungal (Irshad et al., 2019; Orchard, 2019; Pérez et al., 2011).Oil is also used as an ingredient of skin healing creams due to their emollient and anti-ageing properties (Mandawgade & Patravale, 2008; Banerjee et al., 2017).
The essential oils can be used in pharmacology as reagents (Njoroge et al., 2005; Wadhwa & Bakshi, 2013) or for producing product that contribute to good digestion (Wadhwa & Bakshi, 2013).
Today there is a great interest in polyphenols and their induction in the everyday diet and products. They manifest many important biological health properties such as, scavenging free radicals, prevention of oxidation reactions in food and prevention of oxidative stress (Deng et al., 2012, Popa et al., 2008; Ignat et al., 2011; Sagar et al., 2018).
Fruit and vegetable waste represent a valuable source of polyphenols. They exibit anti-cancer,anti-viral, anti-bacterial, anti-oxidative and immune-modulatory effects (Wadhwa & Bakshi,2013, Musarra-Pizzo et al., 2019; Fratianni et al., 2019; Sajadimajd, et al., 2019). Their use is also considered for prevention of neurodegenerative diseases (Renaud & Martinoli, 2019).
