Influence of ultimate muscle pH on the microbial quality of black wildebeest (Connochaetes gnou) meat

Makasi, Thandeka Nedia (2015-12)

Thesis (MSc Food Sc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: The microbial growth, colour stability and pH changes for black wildebeest (Connochaetes gnou) meat under chilled (4.2±0.8°C) vacuum storage were investigated. The investigation centred on the role of ultimate muscle pH on shelf life of the meat. Although bacterial growth was observed over time for both DFD (pH >6) and Normal (pH <6) meat, DFD meat exhibited higher growth rates for lactic acid bacteria (LAB), total viable counts (TVC) and total coliforms. This was attributed to the combination of high pH and possibly the depletion of glucose in the DFD muscles. On the other hand, the growth rate of total coliforms was less than what was observed for the other microorganisms tested. It was assumed that chilled vacuum storage in combination with the high levels of LAB inhibited the growth of total coliforms. Salmonella was not detected in any of the samples analysed. There were no changes in pH during the 12 days storage period for DFD meat whereas pH for Normal meat decreased towards the end of storage possibly due to lactic acid production by LAB. The colour changes were more noticeable in Normal meat (more browning) than in DFD meat after blooming for 30 min. The conclusion for this study was that DFD meat spoiled faster than Normal meat. The meat was further subjected to preservation by oregano essential oil (1% v·v-1). In this case, there was an initial inhibition of TVC, LAB and total coliforms. Furthermore, the growth rates for TVC and LAB were lower (p<0.05) in the oregano oil treatment group than in the control. For total coliforms however, there was only an initial inhibition observed and no effect on the growth rate. Addition of oregano essential oil also resulted in a significant lowering of meat pH. This may have added to the microbial inhibition observed. Based on TVC values, addition of oregano essential oil extended the shelf-life of black wildebeest meat by 3 days. At the beginning of the study, the lipid oxidation (TBARS) values were above the threshold for detection. Also, the percentage of metmyoglobin had exceeded the levels at which browning becomes visible. Therefore, conclusions on the effects of oregano essential oil on the colour and lipid oxidations were not made in this study. However, oregano essential oil inhibited microbial growth and stabilised TBARS throughout the 9 day storage period. Therefore there is potential to use oregano essential oil as a preservative for black wildebeest meat, although more research is needed.

AFRIKAANSE OPSOMMING: In hierdie studie word die mikrobiese groei, stabiliteit en pH kleur verandering ondersoek vir swartwildebeestevleis onder verkoelde (4.2 ± 0.8 ° C) vakuum berging. Die ondersoek is spesifiek gefokus op die rol van die eind-spier pH op die raklewe van die vleis. Alhoewel mikrobiese groei vir beide DFD (pH >6) en Normal (pH <6) vleis waarneembaar was met verloop van tyd, het die DFD vleis hoër groeitempo vir melksuurbakterieë (MSB) en totale lewensvatbare tellings (LVT) getoon. Dit was as gevolg van die kombinasie van hoë pH en die moontlikheid van die vermindering van die glukose in die DFD spiere. Aan die ander kant was dit waargeneem dat die groeikoers van die totale kolivormig bakterieë minder was, teenoor die ander mikro-organismes wat getoets was. Dit was aangeneem dat die verkoelde vakuum stoor die groei van die totale kolivormig bakterieë geïnhibeer het. Salmonella was nie opgespoor in enige van die geanaliseerde monsters nie. Daar was geen verandering in pH tydens die stoor tydperk vir DFD vleis nie, maar die pH vir normale vleis het tydens die einde van die stoor tydperk afgeneem. Die kleur verandering onder vakuum stoor was meer waarneembaar in die normale vleis as wat dit was in die DFD vleis. Die gevolgtrekking van hierdie studie was dat DFD vleis baie vinniger bederf teenoor normale vleis. Maar daar was variasie op die gewig van die oorspronklike mikrobiese lading en dit kon die bakteriese groeitempo van die normale vleis beïnvloed. Die vleis is verder behandel met oregano essensiële olie ( 1 % v·v-1) vir preservering . In hierdie geval, was daar 'n aanvanklike inhibisie van LVT, MSB en totale kolivormig bakterieë. Verder was die groeitempo vir LVT en MSB aansienlik laer (p<0.05 ) in die behandelings groep teenoor die in die kontrole . Vir die totale kolivormig bakterieë was daar egter net 'n aanvanklike inhibisie waargeneem en geen effek op die groeikoers nie. Die byvoeging van oregano essensiële olie het ook gelei tot 'n beduidende verlaging van die pH. Dit kon gelei het tot die mikrobiese inhibisie wat waar geneem was. Gebaseerd op die LVT, het die byvoeging van oregano essensiële olie gelei tot die verlenging van die swartwildebeeste vleis se raklewe met 3 dae. Aan die begin van hierdie studie was die lipied oksidasie (TBARS) waardes bo die drumpel van opsporing. Ook, die persentasie van metmyoglobin het die vlakke waarop verbruining sigbaar word, oorskry. Daar is potensiaal vir die gebruik van oregano essensiële olie as n middel vir die verlenging van swartwildebees vleis, maar nog navorsing is nodig.

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