This study aims to evaluate the potential prebiotic compounds of yellow watermelon, honeydew, and papaya peels by studying their effects on probiotics namely Lactobacillus rhamnosus and Bifidobacterium bifidum. Comparing three peel higher growth for L. rhamnosus and B. bifidum bacteria found from watermelon and honeydew which are 9.90 and 9.82 (log CFU/g dry extract) after 48 hr. Yellow watermelon peel extract also showed significantly higher amounts of indigestible polysaccharides (104.50 mg/g) than the other two peels. Glucose and fructose were the major reducing sugar present with a total of 340.34, 465.25, and 212.25 mg/g of dry peel extracts from yellow watermelon, honeydew and papaya respectively. Honeydew and yellow watermelon peel extract showed the highest hydrolysis of 13.80% and 13.68% and 11.27% and 10.53% to artificial human gastric juice and α‐amylase digestion, respectively. The results indicated that among three fruit peels yellow watermelon peel shows high prebiotic potentiality. Practical applications This study found fruit peels contain a reasonably high amount of potential prebiotic compounds. The polysaccharide extracts of the peel showed a significant effect in stimulating the growth of L. rhamnosus and B. bifidum compared with the controlled study within 48 hr, where polysaccharide extract of yellow watermelon peel proving the most effective because it was able to significantly increase the probiotic bacteria count within 24 hr. In brief, yellow watermelon peel possessed the best prebiotic potential due to its high yield, quick effect in stimulating the growth of probiotic bacteria, high amount of reducing sugar, and indigestible non‐starch polysaccharide while also resist digestion by gastric juice and α‐amylase.

Food supplements are extensively used as a natural remedy to improve human health condition. Considerable progress has been reported recently by several studies to analyse the bioactive substances and their functional activities of fruit by-product. The food industry generates a vast amount of wastes during manufacturing or processing, which are mainly skins, kernels, and seeds. These by-products contain valuable bioactive compounds such as antioxidants, vitamins, minerals, and indigestible food ingredients called prebiotics. Peels from fruits like yellow rambutan, green kiwi, mango, and papaya exhibit a strong anti-proliferative, anti-cardiovascular, anti-oxidant, and hepatoprotective effects due to the presence of bioactive compounds namely flavonoid, B-type catechin dimer, and penta-O-galloyl-glucoside. This review will illustrate a new concept of functional foods by providing information on alternative sources of bioactive compounds from food by-product and their efficacy in human nutrition. This study will also recapitulate the presence of bioactive components in fruit by-product, their way of action, constitution, health benefits, and probable therapeutic action in the treatment of disease prevention.

To date, the waste-to-wealth concept is a common aptitude in the world (Varzakas et al., 2016). The food and agricultural industries all over the world produce a large number of wastes after using the whole fruit, which contains significant amounts of bioactive or functional components, sugar, and dietary fiber (Madhumeena et al., 2021). The utilization of these wastes has become a main concern and challenging aspect because of the higher production of by-products (peels, seeds, leaves, stems, roots, and pomace) during several stages of the processing chain (Mármol et al., 2021). Studies have validated the waste utilization process as a novel, less expensive, economical, and alternative source of food additives, antioxidants, pectin, and organic acids through various extractions and fermentation methods (Roda & Lambri, 2019). In this case, based on recent studies, fruit-by-products have been suggested as an alternative vehicle for probiotic production (Roda & Lambri, 2019;Ruiz Rodríguez et al., 2021).Pineapple, watermelon, and banana are popular tropical fruits in the world; their production per year worldwide was 18.8, 81.2, and 116 million tons, respectively (FAO, 2020;Yang et al., 2016). Their by-products are a rich source of nutritional components, which make them the best suitable candidate to produce new value-added products (Ahmadi & Ganjidoust, 2021;Vicenssuto & de Castro, 2020).The demand for the efficient use of food by-products has increased due to economic and environmental concerns (Yang et al., 2010).According to Food and Agriculture Organization and the World Health Organization (FAO/WHO, 2001), probiotics are "live microorganisms when administered in adequate amounts confer a health benefit on the host". The Coronavirus Disease (COVID-19), which

Summary This study aims to evaluate the prebiotic potential of selected fruit peels (watermelon, pineapple and banana) by studying their effects on growth of probiotic organisms as indicated by viable counts. The effect on probiotic growth was examined using different strains, namely Lactobacillus rhamnosus, L. plantarum and Bifidobacterium bifidum. The growth for L. plantarum and L. rhamnosus in pineapple peel extract (PPE) showed the maximum value of 8.27 and 7.53 log CFU/mL respectively, after 24 h incubation. The study also revealed that PPE contained the highest amounts of indigestible polysaccharides 351.13 mg/g as compared to other peels. The major reducing sugar consisted of glucose and fructose with a total amount of 442.75, 326.05 and 354.14 mg/g in dried peel extract from pineapple, watermelon and banana respectively. Pineapple and banana peel extract exhibited maximum hydrolysis of 9.21% and 8.74% and 32.95% and 30.63% when treated with gastric juice and α‐amylase. This investigation demonstrated that watermelon, pineapple and banana peel extract could be effectively used as prebiotics to improve the growth of beneficial microbes.

In combatting the increase in healthcare costs, at present, one of the preventive approaches to medicine has been developed with the upliftment of new synbiotic products. Synbiotic is the synergistic effect of probiotics and prebiotics which exert multiple beneficial effects and have been increasingly used in preventing or treating human diseases since the last ten years. Several trials have reported that synbiotic therapy could help in the treatment of human disease prevention. PubMed, Science Direct, and Google Scholar were searched by keywords ‘prebiotic’, ‘probiotic’, and ‘synbiotic’ for relevant literature from 2000 to 2020. A total of 58 articles were selected and revised. This paper evaluates the effect of synbiotic supplementation on different diseases, for instance, obesity, insulin resistance syndrome, diabetes, and non-alcoholic fatty liver disease. The progressive knowledge on the outcome of synbiotic supplementation on health, recent trends and developments in this field are summarised. However, further research is required to understand the mechanism of how synbiotics affect in different diseases.