School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemHealth benefits and functional properties of some agro-industrial waste by-products( 2023-03)The fruit processing industry is one of the major industries that generate significant amounts of by-products in the form of peels, core, pomace, and stalks. Every fruit comprises nearly 15-30% peel, the phytochemical profile of these fruit peels is distinct since they contain beneficial substances such as polyphenols, dietary fibers, vitamins, and minerals in significant amounts. Phytochemicals are well known to have multiple benefits to human health. The addition of fruit peels to probiotic yoghurts (and may be to other foods) can play a vital role in enhancing the product nutritional value and physical characteristics. This PhD work aimed at investigating the bioactive profile, prebiotic properties, and potential application of some fruit peels in food products. This project involved three peels obtained from Australian tropical fruits, including mango (Mangifera indica), banana (Musa sapientum), and apples (Malus domestica). Furthermore, the adaptability of using these fruit peels as prebiotics were tested in MRS growth media against three strains of lactic acid bacteria (LAB). The included LAB were Lactobacillus rhamnosus (LGG), Lactobacillus casei (LC 431), and Bifidobacterium animalis subsp. lactis (Bb-12). The viability of activated probiotic reached more than 10 logs CFU/ml, using both mono-strain and multi-strains analyses of probiotic preparations. The probiotics were fortified with different concentrations (0%, 2%, 4%) of fruit peel powders (FPP). Mango peel powder (MPP) and banana peel powder (BPP) presented significantly (p < 0.05) enhanced prebiotic efficacy than apple peel powder (APP). Moreover, results revealed that increasing the concentration of added FPP from 2% to 4% imparted insignificant differences (p > 0.05) on the mean count of probiotics. Hence, 2% concentration of fruit peel powders was selected to be used in probiotic yoghurt formulations. The various yoghurt mixes and treatments used in this study involved, control yoghurt, banana peel fortified yoghurt, mango peel fortified yoghurt, yoghurt enriched with 1% each of three probiotic strains, banana peel and probiotics enriched yoghurt, mango peel and probiotics enriched yoghurt. The co-administration of selected fruit peels and probiotics in fresh and freeze-dried yoghurts powders showed significant increase (p < 0.05) in relation to the nutritional characteristics and bioactive potential of yoghurts during storage. Moreover, MPP and BPP enriched fresh yoghurts presented insignificant increase (p > 0.05) in the storage stability of S. thermophillus and B. lactis during 28 days of refrigerated storage (4 oC). Analyses and identification of the phenolic profile of plain MPP and yoghurts fortified with MPP using LC-ESI-QTOF-MS/MS techniques showed a total of 108 polyphenols. Furthermore, the in vitro gastrointestinal digestion of plain MPP and MPP fortified yoghurts, revealed gradual decline in the total phenolic and antioxidant contents and an increase in the inhibition of alpha-glucosidase enzyme activity. Results confirmed also that the dairy matrix in yoghurt and probiotic fermentation caused a significant increase (p < 0.05) in the bioaccessibility (refers to the percentage of polyphenols released, solubilized in digestive juice, and available for absorption) of polyphenols in MPP fortified yoghurts in comparison with plain MPP. The fecal fermentation of indigestible fraction of MPP was carried out using human fecal inocula, which resulted in a range of phenolic catabolites along with the biosynthesis of short-chain fatty acids, decreased pH, and enhanced counts of Bifidobacteria. Furthermore, 16s rRNA gene sequencing demonstrated that both plain MPP and fortified MPP-yoghurts caused significant shifts in the microbiota-modulating properties in the gut. Similarly, the in vitro bioaccessibility studies of polyphenols during the gastrointestinal digestion and fermentation of plain BPP and BPP enriched yoghurts presented the same trend of phenolic bioaccessibility as that of MPP. However, the identified phenolic compounds and their calculated concentrations were different from those detected with MPP. Such variations could be attributed to the natural differences in chemical composition and phytochemical contents in different peels. The characterization of apple peel powder (APP) under in vitro digestion conditions tentatively identified 88 phenolic compounds, 34 of them were bioaccessible during the gastrointestinal digestion. The breakdown of bound polyphenolic fraction and fiber during the in vitro fermentation of APP produced acetic acid as the most abundant short-chain fatty acid along with a significant release of small phenolic metabolites. The findings of this research demonstrated that fruit processing by-products can be fully utilized as good sources of various phytochemicals and fiber. The application of such neglected sources of nutrients can be extended beyond the dairy products to include a wider range of food applications including the bakery, soup, snack, and even meat products.