Browsing by Author "Pfukwa, Trust Mukudzei"
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- ItemPhytochemical analysis, antioxidant and antimicrobial effects of extracts from grape (Vitis vinifera) by-products and mandarin orange (Citrus reticulata Blanco)(Stellenbosch : Stellenbosch University, 2018-12) Pfukwa, Trust Mukudzei; Mapiye, Cletos; Fawole, Olaniyi Amos; Manley, Marena; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.ENGLISH ABSTRACT: The increase in level of customer sophistication, motivated by a general interest in healthier food options, has seen growing focus on fruit by-products processing and value addition as a potential source of natural preservatives. In this study, the phytochemical composition, pH, titratable acidity, antioxidant and antimicrobial properties of extracts from orange peel and pulp (OPE), grape pomace (GPE) and seeds (GSE) grown in South Africa were analysed. Spectrophotometric methods were used to quantify total phenols, total tannins, flavonoids, anthocyanins, proanthocyanidins, as well as ascorbic acid and total carotenoids. The pH was measured using a laboratory pH meter while a titrosampler was used to measure the titratable acidity. Antioxidant properties were evaluated using the 2,2-diphenyl-1-picrylhydrazyl radical-scavenging method, ferric reducing-antioxidant power test, oxygen radical absorbance capacity assay and the lipoxygenase inhibition assay. Comparisons were made against ascorbic acid used commercially as an antioxidant preservative. The antimicrobial properties were evaluated against five bacteria (Listeria monocytogenes, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa) and one yeast (Candida albicans) using the broth microdilution method with comparisons against tetracycline (positive indicator) and sodium metabisulphite (artificial antimicrobial preservative). Total phenols and carotenoids were highest in GPE followed by GSE and OPE (p ≤ 0.05). Flavonoids and anthocyanins were higher (p ≤ 0.05) in GPE and GSE compared to OPE. The GSE had highest proanthocyanidins followed by GPE and OPE (p ≤ 0.05). Ascorbic acid was only detected in OPE, which also had the highest titratable acidity and lowest pH (p ≤ 0.05). The GSE had the highest antioxidant activity based on all four antioxidant assays, as evident in GSE having the highest antioxidant potency composite index followed by GPE and OPE (p ≤ 0.05). The extracts showed less antimicrobial activity compared to the positive indicator and artificial antimicrobial preservative. Greatest antimicrobial activity among the extracts, however, was shown by OPE. The order of antimicrobial activity of the extracts was OPE > GSE > GPE (p ≤ 0.05). Current findings show that GSE is a potential antioxidant while OPE holds promise as an antimicrobial for the food industry. Overall, valorisation of fruit processing by-products is a promising avenue for enhancing food preservation and shelf life stability while offsetting environmental problems due to waste dumping.