Bioprospecting South African indigenous fruits byproducts as natural antioxidants in processed meat products

Thesis (PhDFoodSc)--Stellenbosch University, 2022.

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.

AFRIKAANSE OPSOMMING: Namate die wêreldwye geriefsvoedselkleinhandelmark groei, neem voedselverliese as gevolg van oksidatiewe agteruitgang toe, wat die vraag na preserveermiddels verhoog. Boonop eis verbruikers veilige natuurlike antioksidante, aangesien sintetiese antioksidantverbruik gekoppel is aan nadelige gevolge vir die gesondheid. Die huidige studie het ten doel gehad om die potensiaal van inheemse vrugte-byproduk-ekstrakte as natuurlike antioksidante in verwerkte vleisprodukte te bepaal. Suid- Afrikaanse inheemse vrugte, waaronder Carissa macrocarpa A.DC., Diospyros whiteana (Hiern) F.White, Dovyalis cafffra Warb., Harpephyllum caffrum Bernh., Olea europaea L. var. africana (Mil.) P.S.Green, Colpoon compressum P.J.Bergius en Syzygium guineense DC. is versamel uit Kirstenbosch Botaniese Tuin in Kaapstad, Suid-Afrika. Eerstens is die fenoliese inhoud van ru- ekstrakte van gevriesdroogde saad en skil/pulp van elke vrug geëvalueer met behulp van UPLC-ESI- Q-TOF/MS en hul in vitro chemiese antioksidantaktiwiteit bepaal met behulp van vier antioksidant- toetsings, naamlik; DPPH, FRAP, ORAC en lipoksigenase inhibisie. Tweedens is die effek van suiwering, met behulp van XAD7HP-makroporeuse hars en vrugtipe (H. caffrum skil, HCP vs. S. guineense, SGS) op die fenoliese samestelling en in vitro chemiese antioksidantaktiwiteit van die uittreksels geëvalueer en opgevolg met 'n Caco-2-selgebaseerde metode. Die potensiaal van HCP- gesuiwerde ekstrakte (HCP-PE, 250 ppm, 450 ppm en 650 ppm), om Saccharomyces cerevisiae teen H2O2-geïnduseerde spanning te beskerm met behulp van RNA-volgorde (RNA-seq) is toe ondersoek. Laastens is die in-produk-antioksidant-effektiwiteit van HCP-PE by 0, 250, 450 en 650 ppm om rakstabiliteit (kleurstabiliteit, myoglobienoksidasie, TBARS, koolstofvorming en thiolverlies) en sensoriese kwaliteit van beesvleis ‘patties’, geëvalueer in vergelyking met natriummetabisulfiet (SMB). Die bevindings het getoon dat hidroksikaneelsuur en totale fenoliese konsentrasie (TPC) die hoogste was in D. caffrasaad, terwyl flavonoïede, antosianiene, hidroliseerbare tanniene, en proantosianidiene die hoogste was in die ru-ekstrakte (CE) van C. compressumsaad, Olea africana- pulp, SGS en HCP, onderskeidelik (P ≤ 0,05). Die HCP-CE het die hoogste FRAP- en lipoksigenase- aktiwiteit gehad, terwyl SGS-CE die hoogste DPPH-aktiwiteit gehad het (P ≤ 0,05), wat die potensiaal toon vir verdere evaluering van antioksidante. Suiwering het HCP TPC met 200% verhoog, terwyl 'n afname van 20% vir SGS (P ≤ 0,05) waargeneem is. Die HCP-PE het die hoogste chemiese antioksidantaktiwiteit oor die suiwering × vrugtetipe interaksies gehad. Ongeag die konsentrasie, was HCP-PE sellulêre antioksidantaktiwiteit vergelykbaar met dié van SMB (P > 0,05). Die HCP-PE sitotoksiese effekte het (P ≤ 0,05) op 'n dosisafhanklike manier toegeneem, maar was laer (P ≤ 0,05) as dié van SGS en SMB. Die HCP-PE het ribosoombiogenese en splicesoom beïnvloed, wat die primering van S. cerevisiae moontlik maak vir doeltreffende oksidatiewe stresreaksie en -herstel. Die neiging tot sitotoksisiteit het toegeneem met 'n hoë HCP-PE-konsentrasie (650 ppm) wat lei tot proteasomale en pro-apoptotiese aktiwiteit (P ≤ 0,05). Die HCP-PE het kleur, TBARS, koolstofvorming en tiolverlies verbeter in vergelyking met die beheer (P ≤ 0,05), met geen noemenswaardige verskil in die uitvoering van HCP-PE-behandelings (P > 0,05). Wat die sensoriese kwaliteit betref, het HCP-PE (P ≤ 0,05) sagtheid en sappigheid verminder, terwyl ongewenste geure (P ≤ 0,05) in beesvleis ‘patties’ toegeneem het in vergelyking met beheer en SMB. Die getuienis het saam getoon dat Suid-Afrikaanse inheemse vrugte-ekstrakte, veral HCP-PE op 450 ppm, 'n bron is van veilige antioksidante vir voedseltoepassings. Hierdie werk het 'n grondslag gelê vir die valorisering van inheemse vrugte-byprodukte as natuurlike antioksidante vir wyer voedseltoepassings.

Doctorate