The addition of rooibos tea extract (Aspalathus Linearis) as a natural antioxidant to South African Droëwors

Thesis (MSc Food Sc)--Stellenbosch University, 2013.

ENGLISH ABSTRACT: The effect of rooibos tea (Aspalathus linearis) extract (RBTE) as a natural antioxidant on the lipid and protein stability and sensory profile of traditional South African droëwors (dried sausage) was investigated. Ostrich meat (Struthio camelus) and pork back fat was used in the initial study as the meat and fat sources. Four treatments were prepared with each treatment increasing in concentration of RBTE: RBTE 0%, RBTE 0.25%, RBTE 0.50% and RBTE 1.0%. The lipid stability of the droëwors increased after drying with RBTE 0.25% having lower TBARS than the other treatments. The protein stability and heme-iron results of the droëwors did not differ (P > 0.05) between treatments. The second study investigated the effect of added RBTE to droëwors of three different game species namely, blesbok (Damaliscus pygargus phillipsi), springbok (Antidorcas marsupialis) and fallow deer (Dama dama). No significant effects (P > 0.05) were seen between treatments in terms of the lipid and protein oxidation of the dried product within a species. Protein oxidation increased after drying but did not differ (P > 0.05) between the treatments within a stage (raw or dried) within species. Using different meat sources to the initial study and a shorter drying period did not result in any differences between treatments however, RBTE 0.25% did give the best results for lipid stability after drying. Heme-iron concentration differed (P < 0.05) between the RBTE treatments within the dried stage within a species with RBTE concentrations being inversely correlated with the levels of heme-iron. The final study investigated the addition of RBTE to blesbok and springbok droëwors using an improved formulation, drying parameters and a different (beef) fat source. The results indicated that RBTE 1.0% significantly (P < 0.05) slowed down lipid oxidation after a two week storage. The added RBTE, however, did not result in any significant differences (P > 0.05) in protein oxidation and heme-iron concentration. A positive correlation between lipid oxidation and heme-iron concentration was noted. Throughout the study the proximate composition analyses gave consistent results with the drying procedures. When the total moisture content decreased after drying, the fat and protein content became more concentrated. There were no differences (P > 0.05) between the moisture, protein and fat contents between treatments within a specific stage. High concentrations of oleic acid, stearic acid, linoleic acid and palmitic acid were detected. The fatty acid profile suggests that after drying there is a decrease in polyunsaturated fats which could explain the increase in lipid oxidation. With the addition of RBTE, differences in sensory attributes between the different droëwors treatments were detected by a trained panel. From these results it can be concluded that RBTE can be marketed as a natural antioxidant for use in droëwors. The composition of the RBTE particularly as pertaining to the levels of aspalathin and quercetin should however be considered when evaluating the level of RBTE to use.

AFRIKAANSE OPSOMMING: Die studie het die invloed van rooibostee-ekstrak (Aspalathus linearis) (RBTE) as ʼn natuurlike anti-oksidant op die oksidatiewe stabiliteit van tradisionele Suid-Afrikaanse droëwors ondersoek. Aanvanklik is volstruis vleis (Struthio camelus) in kombinasie met varkrugvet gebruik. Daar is vier behandelinge voorberei met toenemende konsentrasies van RBTE (RBTE 0%, RBTE 0.25%, RBTE 0.50%, en RBTE 1.0%). Die lipiede het ʼn hoër stabiliteit getoon na die drogingsproses, veral die 0.25% RBTE behandeling wat die beste resultate gelewer het. Die verskillende behandelings het geen uitwerking op die stabiliteit van die proteïene en die heem-yster konsentrasies gehad nie. In die tweede studie is die invloed van RBTE in blesbok (Damaliscus pygargus phillipsi), springbok (Antidorcas marsupialis) en takbok (Dama dama) droëwors ondersoek. Die RBTE het geen effek getoon op die oksidatiewe stabiliteit van die verskillende gedroogde behandelings van elke spesie nie. Die proteïenoksidasie het wel toegeneem as gevolg van die vogverlies tydens die drogingsproses, maar het nie verskil (P>0.05) tussen die verskeie behandelings van die spesifieke spesies nie. Die 0.25% RBTE behandeling het weereens die beste resultate gelewer in terme van die lipiedstabiliteit na droging. Daar was verskille in die heem-yster konsentrasies tussen die verskeie gedroogde RBTE behandelings van elke spesie, wat weer goed gekorreleer het met die oksidasiestabiliteit. Die finale studie het die insluiting van RBTE in blesbok en springbok droëwors ondersoek. Die formulasie en drogingsparameters is verbeter en ʼn ander bron van vet (bees) is gebruik. Daar is gevind dat die insluiting van 1.0% RBTE die lipiedokisidasie betekenisvol verminder het na ʼn stoortydperk van 2 weke. Verder het dit geen effek (P>0.05) op beide die proteïenoksidasie en heem-yster konsentrasie gehad nie. Die lipiedoksidasie en heem-yster het wel ʼn positiewe korrelasie getoon. In algeheel het die proksimale samestelling van die droëwors konsekwente resultate gelewer. Daar was ʼn afname in die totale voginhoud as gevolg van die drogingsproses met ʼn toename in vet- en proteïeninhoud. Geen verskille in terme van die vog-, proteïen- en vetinhoud is tussen die verskeie rou en gedroogde behandelinge gevind nie. Die vetsuurprofiel toon hoë konsentrasies oliensuur, steariensuur, linoliensuur en palmitiensuur. Daar was wel ʼn afname in die poli-onversadigde vetsure na die drogings proses wat dien as ʼn moontlike verklaring van die toename in lipiedoksidasie. Die insluiting van RBTE in droëwors het gelei tot verskille in die sensoriese eienskappe van die verskeie droëwors behandelings. In geheel het die studie bewys dat RBTE gebruik en bemark kan word as ʼn natuurlike anti-oksidant in gedroogde vleis produkte. Dit is egter noodsaaklik dat die samestelling van die RBTE in ag geneem moet word, veral met betrekking tot die vlakke van spesifieke anti-oksidante soos aspalatien en kwersetien.

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