Microbial, Biochemical and Food Biotechnology
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Browsing Microbial, Biochemical and Food Biotechnology by Author "Banda, Thabo"
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Item Open Access Evaluation of the optical density reading for the determination of shelf life of whole chicken carcasses by the enumeration of the microbial contamination levels(University of the Free State, 2003-11) Banda, Thabo; Bragg, R. R.; Viljoen, B. C.English: Increased media and public interest over meat contamination have highlighted the need for continual improvements in this regard in the poultry industry. In spite of all the effort and money placed into research on microbial contamination of poultry carcasses, it is still not possible to produce carcasses, which are free of spoilage and pathogenic microorganisms. Carcasses are mostly contaminated during processing, contributing to the presence of high number of mesophilic microorganisms. The spoilage microorganisms cause consumers to reject the product due to appearance, off odour or undesirable flavour whereas the pathogenic microorganisms may lead to health hazards. The Standard plate counts methods have been the method of choice for the enumeration of contaminating microbial populations in the poultry industry. However, these methods are laborious and time consuming. In this study, optical density (OD) reading as a microbial enumeration method on poultry carcasses was established and evaluated for its application as a rapid, alternative method. In chapter 2, the dominant microorganisms were isolated and identified from eviscerated poultry carcasses. The carcasses were sampled by whole carcass rinse method and bacteria were isolated on Plate Count Agar at 27oC for 48 h. A total of five different species were identified, based on their prevalence in the sample and were identified by conventional methods. The identification of the isolates was further confirmed by API techniques. The dominant species were Escherichia coli, Shewanella putrefaciens, Aeromonas hydrophila, Serratia marcescens and Staphylococcus aureus. Mean counts (log10 cfu/g) of these organisms were 3.08, 1.48, 0.85, 1.74, and 1.21 respectively. In chapter 3, OD readings as an enumeration method was established. This required the establishment of a number of parameters, which include: 1) Determining the wavelength to be used throughout this study. This achieved by scanning the medium through the spectra of 200-700 nm and a wavelength of 420 nm was selected as the optimal wavelength. 2) Determination of incubation time, which was achieved by the construction of separate growth curves for each isolates and determine the time when all isolates were in the exponential phase of growth. A time of 4 h was selected. 3) Evaluation of the repeatability of the OD readings of each isolate. Both pure culture and mixed culture were evaluated. The coefficients of variation for repeatability evaluations had coefficients of variation less than 15% for pure culture. Similar coefficients of variation values was obtained with mixed cultures and most values were even below 10%. 4) The correlation of OD reading evaluated after 4 h incubation at 37oC to standard plate counts (incubated in PCA at 37oC for 24 h). The scatter plots graph obtained in this study had had a positive strong correlation, which was above 0.9 for all isolates, except for Serratia marcescens, which had the correlation coefficient of 0.886. The high repeatability and correlation showed high potential of the OD in enumeration, hence the further objective of the involved evaluating the method on chicken carcasses. In chapter 4, carcasses were sterilized, followed by artificially inoculation with known microorganisms at different load. Sterilization was evaluated by examining different concentrations of Virukill solution at different concentration. Virukill is a non-toxic, highly effective disinfectant. High concentration (1, 2 & 3 v/v%) of this disinfectant was effective in eradicating all microbial population under the applied conditions. It was established that at these high levels, substantial residual effects were found which prevented the re-inoculation of chicken carcasses. With lower concentrations, it was established that a 0.3 v/v% of Virukill eradicated all microorganisms and did not have residual effect, thus allowing re-inoculation of the carcasses with known concentrations of bacteria. A correlation coefficient between standard plate counts and the OD reading method of 0.903 and 0.968 were found for mixed cultures determined by whole carcass rinse and neck skin sampling methods, respectively. A. hydrophila, had correlation coefficient of 0.849 and 0.985 for whole carcass rinse and neck skin respectively. Similarly Serratia marcescens had 0.993 and 0.940 for whole rinse and neck skin respectively. The results found in this study clearly show that bacterial enumeration through the use of OD readings is capable of reducing time and labour required to obtain the initial microbial load after processing of the carcasses. The OD method evaluated on artificially contaminated carcasses is promising. The method shows great potential for enumeration of bacteria during routine evaluation at the poultry processing plant.