Browsing by Author "Pfukwa, Trust Mukudzei"

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    Bioprospecting South African indigenous fruits byproducts as natural antioxidants in processed meat products
    (Stellenbosch : Stellenbosch University, 2022-12) Pfukwa, Trust Mukudzei; Mapiye, Cletos; Manley, Marena; Fawole, Olaniyi A; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: As the global convenience food retail market grows, food losses due to oxidative degradation are on the rise, increasing the demand for preservatives. Additionally, consumers are demanding safe natural antioxidants as synthetic antioxidant consumption has been linked to adverse health effects. The current study aimed to determine the potential of indigenous fruit byproduct extracts as natural antioxidants in processed meat products. South African indigenous fruits including Carissa macrocarpa A.DC., Diospyros whyteana (Hiern) F.White, Dovyalis caffra Warb., Harpephyllum caffrum Bernh., Olea europaea L. var. africana (Mill.) P.S.Green, Colpoon compressum P.J.Bergius, and Syzygium guineense DC. were collected from Kirstenbosch National Botanical Garden in Cape Town, South Africa. Firstly, the phenolic content of crude extracts from lyophilised seed and peels/pulp of each fruit were evaluated using UPLC-ESI-Q-TOF/MS and their in vitro chemical antioxidant activity determined using four antioxidant assays namely; DPPH, FRAP, ORAC and lipoxygenase inhibition. Secondly, the effect of purification, using XAD7HP macroporous resin, and fruit type (H. caffrum peel, HCP vs. S. guineense, SGS) on the phenolic composition and in vitro chemical antioxidant activity of the extracts was evaluated and followed up with a Caco-2 cell-based method. The potential of HCP-purified extracts (HCP-PE, 250 ppm, 450 ppm and 650 ppm), to protect Saccharomyces cerevisiae against H2O2-induced stress using RNA sequencing (RNA-seq) was then investigated. Lastly, the in producto antioxidant efficacy of HCP-PE at 0, 250, 450 and 650 ppm to enhance shelf stability (colour stability, myoglobin oxidation, TBARS, carbonyl formation and thiol loss) and sensory quality of beef patties was evaluated in comparison with sodium metabisulfite (SMB). The findings showed that hydroxycinnamic acids and total phenolic concentration (TPC) were highest in D. caffra seed, while flavonoids, anthocyanins, hydrolysable tannins, and proanthocyanidins were highest in the crude extracts (CE) from C. compressum seed, Olea Africana pulp, SGS and HCP, respectively (P ≤ 0.05). The HCP-CE had the highest FRAP and lipoxygenase activity, while SGS-CE had the highest DPPH activity (P ≤ 0.05), showing potential for further antioxidants evaluation. Purification increased HCP TPC by 200 %, while a 20 % decrease was observed for SGS (P ≤ 0.05). The HCP-PE had the highest chemical antioxidant activity across the purification × fruit type interactions. Regardless of concentration, HCP-PE cellular antioxidant activity was comparable to that of SMB (P > 0.05). The HCP-PE cytotoxic effects increased (P ≤ 0.05) in a dose-dependent manner but were lower (P ≤ 0.05) than that of SGS and SMB. The HCP- PE influenced ribosome biogenesis and spliceosome, enabling the priming of S. cerevisiae for efficient oxidative stress response and recovery. The tendency towards cytotoxicity increased at high HCP-PE concentration (650 ppm) leading to proteasomal and pro-apoptotic activity (P ≤ 0.05). The HCP-PE improved colour, TBARS, carbonyl formation and thiol loss compared to the control (P ≤ 0.05), with no significant difference in the performance of HCP-PE treatments (P > 0.05). Regarding sensory quality, HCP-PE reduced (P ≤ 0.05) tenderness and juiciness, while undesirable flavours increased (P ≤ 0.05) in beef patties compared to control and SMB. Taken together, the evidence showed that South African indigenous fruits extracts, particularly HCP-PE at 450 ppm, are a source of safe antioxidants for food applications. This work has laid a foundation for valorisation of indigenous fruit byproducts as natural antioxidants for wider food applications.
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    Phytochemical 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.