Today, the challenge of the future is to produce adequate food for an ever-increasing population, thereby ever-decreasing the area of cultivatable land available to meet the increased food demand. It is very important to keep food production in harmony with the environment. There are various modern processing techniques that produce a significant amount of by-products that are now being used as fertilizers or just dumped in order to reduce the problems of pollution. According to a United Nations Environment Programme (UNEP) Report in 2019, an estimated 931 million tonnes of food were either lost or wasted globally. The Indian households accounted for 7.4 percent of the 931 million tonnes of food that were wasted in the year 2019 across the globe. Every year, an average household had wasted about 74 kg of food. In India, it was 50 kg per household (68.8 million tonnes a year). In comparison, the United States squandered 59 kg per household (19.4 million tonnes), while China squandered 64 kg per household (91.6 million tonnes). Food waste occurs at all stages of production, right from the farms and food processing facilities to supermarkets, residential buildings, institutes, industries and restaurants. The average household food waste generated across the globe, including the household food waste generated in different fields are demonstrated in Figures 1 and 2.
The cost for handling such waste is increasing day by day. A point may also be reached where handling food waste becomes economically feasible and the costs can be recovered from the waste to produce by using potentially valuable and edible bioactive compounds (Weihrauch et al., 1994). Waste by-products are usually the fruits and vegetables, which are the most utilized commodities. With the growing population and change in diet habits of each and every individual, the production and processing of horticultural crops, especially fruits and vegetables have increased significantly to fulfil their increasing demand worldwide.
In spite of high production and consumption, there are significant losses that arise from the waste that is generated by them at different stages starting from when the produce is fresh, including the waste that is generated from domestic households, commercial premises and in the processing industries, which has been causing serious nutritional, economic and environmental issues. Fruit and vegetable wastes have rich sources of phytochemicals and bioactive compounds. Additionally, seed, skin, rind and pomace contain good sources of potentially valuable bioactive compounds such as carotenoids, polyphenols, dietary fibres, vitamins, enzymes, oils, etc., Hence, these bioactive compounds can be produced and utilized in the areas where there is shortage of supply in food components (Sagar et al., 2018; Galanakis, 2012). These phytochemicals can be utilized in different industries, including the food industry for the development of functional or enriched foods, the health industry for medicines and pharmaceuticals and the textile industry among others. The use of waste for the production of various crucial bioactive components is an important step towards sustainable development. Over the last two decades, there are increasing signs of progress happening across the globe through the conversion of waste products into much more valuable products. The recovery of bioactive compounds from by-products of food processing needs to be recovered as high-added-value components by utilizing emerging technologies and also has to be commercialized for their application (Sagar, et al., 2018). The following are some of the bioactive components that can be counted as examples of important biomolecules that can be obtained from fruit and vegetable waste. Figure 3 illustrates the various possible applications of fruit and vegetable wastes.
IMPORTANT BIOACTIVE COMPOUNDS
Flavour and Aroma Extracts
The waste materials from fruits and vegetables are important sources of various bioproducts that also serve to be used as a source of flavours and aromas. Fruit peel is a by-product and potential source to extract natural aroma and flavouring compounds. Additionally, there are a wide number of applications of fruit peel aroma extract in food, pharmaceutical and cosmetic industries. Grape peel is rich in volatile compounds and is responsible for the fruity fresh aroma and flavour of grape and wine (Sánchez-Palomo et al., 2005). Apple is a widely consumed fruit where over 20 aroma compounds have had a decisive impact on its aroma character. These compounds comprise of carboxylic esters, alcohols, aldehydes, ketones, acids and others, but only 20 of them have a decisive impact on the overall aroma character (Ferreira et al., 2009). Citrus peel constitutes almost one-half of the total fruit mass, presenting itself as an important source of various pleasant aroma compounds with monoterpene and sesquiterpene hydrocarbons as the majority (Asikin et al., 2012). Similarly, dried mango peel powder is also considered as a flavouring agent endowing yogurt with characteristic mango odours (Ruiz et al. 2011), while dried apple peel powder was claimed to impart the desired aroma and flavour to biscuit (Rahman et al. 2020).
Therapeutic properties of bioactive compounds derived from fruits have wide applications, some of them being anticancer, antidiabetic, antihypertensive, anti-inflammatory, antimicrobial, antioxidant, etc. (Van Breda and de Kok, 2018). The avocado by-products such as peel and seed extracts can be used as an antioxidant and they also have anti-inflammatory properties (Tremocoldi et al., 2018). Pomegranate peel extract prevented bone loss that was reported through the mice model of osteoporosis and stimulated osteoblastic differentiation in-vitro study (Spilmont et al., 2015). The isolate of bromelain extracted from the pineapple peel showed the recovery and purification of the enzyme by maintaining its specific activity (Bresolin et al., 2013). Similar studies have been reported in the literature showing the importance of the bioactive compounds found in different fruit waste.
A large amount of peel waste is generated from fruit and vegetable-based industries and household kitchens and this has led to a big nutritional as well as economic loss and environmental problems. The peel extracts contain bioactive substances that are highly valuable, which can be further used for different applications. The bioactive compounds extracted from waste show their application in various industries such as the food industry to develop edible films, probiotics and other industries for producing valuable products (Kumar et al., 2020). Hence, another scientific area is emerging within the large field of food science and technology – bio residues valorisation (Martins and Ferreira, 2017). The fruit wastes can be used as novel packaging materials, owing to their oxygen-impermeable properties. The waste generated from vegetables and fruits can be used in the food industry as a substitute for wheat flour and can also be added in the cakes, including using them in the beverage industry (Singh and Kaur, 2015).
Edible waste cutlery
Plastic cutlery is a convenient choice, disastrous to the environment as well as harmful to health. Being a petroleum by-product, the presence of toxins and carcinogens can be easily absorbed into the human body. By-products of jack fruit such as its shaft, skin, latex and seeds are widely used in the production of various value-added products such as edible cutlery, edible films, leather and bakery products such as cookies, waffles and cones (Hussain et al., 2020). In India, the company Bakeys founded by Narayana Peesapaty produces edible cutlery (spoons, forks and even chopsticks) made out of dried millets (jowar), rice and wheat.
Japanese designer Nobuhiko Arikawa owned Rice-Design Company has created edible tableware for Orto Cafe in Japan. The plates, bowls and chopsticks are intended to replace disposable paper tableware. The pieces are made from hardtack, a biscuit dough made from flour, water and table salt, shortening and yeast, no eggs or dairy products are used (Natarajan et al., 2019).
Phenolic compounds are diversified group of phytochemicals which are disseminated in plants i.e. fruits, vegetables, tea, olive oil, etc., (Ignat et al., 2011. Most importantly, it plays a key role in preventing colon cancer, obesity, coronary heart disease, gastrointestinal disorders and risk of diabetes (Jitaru et al., 2005; Luthria and Pastor-Corrales, 2006; Altiok et al., 2008; Ross et al., 2009). Phenolic compounds are categorized into various classes such as flavonoids (subclasses include: flavonols, flavanones, flavones, flavanonols, isoflavones, flavonols, and anthocyanidins), tannins, stilbenes, phenolic acids, and lignans (Hollman et al., 1999; Robbins, 2003). The peel and seeds of fruits and vegetables possess a high amount of these phenolic compounds. In the case of vegetable wastes, potato peel was reported as a good source of phenolic compounds, as it possesses 50% of phenolics out of the whole bioactive components (Friedman, 1997). Cucumber peel was reported as a cheap source of flavonoids for industrial purposes (Agarwal et al., 2012). A large quantity of bananas is produced annually and its peel, which accounts for about one-third of the fruit weight, is mostly discarded as waste. The peel has been traditionally used for the treatment of various ailments. These by-products are rich in phenolics with over 40 individual compounds identified. Phenolics have been found to possess potent antioxidant and antimicrobial properties and are linked with various health benefits (Vu et al., 2018).
This article highlights the significance of the losses that are incurred on account of food waste being generated from fruits, vegetables and other agricultural products. The food waste that arises in large numbers during industrial processing, apart from wastes generated in residential areas, institutional wastes and at restaurants represent a serious problem, since they affect the environment negatively and need to be managed and/or utilized effectively. With the wastes being significant in number, such huge amounts of lost and wasted fruits and vegetables can be effectively used for the recovery and production of multiple bioproducts. Thus, they have the potential to be a novel, renewable, sustainable and a low-cost raw material (source) for the production of several value-added products. There is significant potential for their use as bio fertilizers, dietary fiber, animal feed, industrial enzymes, a substrate for bioactive compounds production, synthesis of nano materials and in producing clean energy (from residual biomass). Hence, there is a necessity to utilize more novel techniques concerning the waste materials that can be converted for their efficient use, as they would be finding higher usage in food, pharmaceuticals, cosmetics, agricultural and chemical industries.
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About the Authors:
Dr. P. Kiran Kumar
Assistant Professor, ATME College of Engineering,
Mysuru 570028, India.