Phytochemical analysis, antioxidant and antimicrobial effects of extracts from grape (Vitis vinifera) by-products and mandarin orange (Citrus reticulata Blanco)

Pfukwa, Trust Mukudzei (2018-12)

Thesis (MScFoodSc)--Stellenbosch University, 2018.

Thesis

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.

AFRIKAANSE OPSOMMING: Die toename in die vlak van verbruikers se gesofistikeerdheid, gemotiveer deur 'n algemene belangstelling in gesonder kos-opsies, het toenemende fokus begin plaas op die verwerking van en dus waardetoevoeging tot vrugtebyprodukte wat as 'n potensiële bron van natuurlike preserveermiddels gebruik kan word. In hierdie studie is die fitochemiese samestelling, pH, titreerbare suurheid, antioksidante en antimikrobiese eienskappe van ekstraksies van lemoenskil en -pulp (OPE), druiwepulp (GPE) en -pitte (GSE) verbou in Suid-Afrika, ontleed. Spektrofotometriese metodes is gebruik om totale fenole, totale tanniene, flavonoïede, antosianiene, pro-antosianidiene, sowel as askorbiensuur en totale karotenoïede te kwantifiseer. Die pH is gemeet met behulp van 'n laboratorium pH meter, terwyl 'n titrosampler gebruik is om die titreerbare suurstof te meet. Antioksidant eienskappe is geëvalueer deur gebruik te maak van die 2,2-difenyl-1-pikrylhidrasiel radikaal-opruimingsmetode, die reduksie-antioksidant kragtoets, die suurstof-radikaal absorbansiekapasiteitsassessering en die lipoksigenase-inhibisie-toets. Vergelykings is gemaak teen askorbiensuur wat kommersieel gebruik word as 'n antioksidant preserveermiddel. Die antimikrobiese eienskappe is geëvalueer teen vyf bakterieë (Listeria monocytogenes, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa) en een gis (Candida albicans) met behulp van die sous-mikroverdunningsmetode met vergelykings teen tetrasiklien (positiewe aanwyser) en natrium metabisulfiet (kunsmatige antimikrobiese preserveermiddel). Totale fenole en karotenoïede was die hoogste in GPE, met laer vlakke in GSE en OPE. Flavonoïede en antosianiene was hoër in GPE en GSE, wanneer vergelyk met OPE. Die GSE het die hoogste pro-antosianidien inhoud, met laer vlakke gevind in GPE en OPE. Askorbiensuur is slegs in OPE gevind, wat ook in die bron die hoogste titreerbare suurheid en laagste pH gehad het. Die GSE het die hoogste antioksidant aktiwiteit op grond van al vier antioksidant-toetse gehad, soos blyk uit GSE wat die hoogste saamgestelde indeks van antioksidant potensiaal het, gevolg deur GPE en OPE. Die onderskeie ekstraksies het minder antimikrobiese aktiwiteit getoon in vergelyking met die positiewe indikator en kunsmatige antimikrobiese preserveermiddel. Die grootste antimikrobiese aktiwiteit onder die ekstraksies is egter deur OPE getoon. Die volgorde van antimikrobiese aktiwiteit van die uittreksels was OPE> GSE> GPE. Huidige bevindinge toon dat GSE 'n potensiële antioksidant is, terwyl OPE belofte as 'n antimikrobiese verbinding vir die voedselbedryf inhou. In geheel, die waardetoevoeging tot die byprodukte van verwerkte vrugte het potensiaal om by te dra tot die verbetering van voedselbehoud en rakleeftydstabiliteit, terwyl die omgewingsprobleme weens afvalstorting ook hiermee aangespreek kan word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105231
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