Call number: LD2668 .T4 1957 F73 / Master of Science

Use of the bioluminometric ATP assay was evaluated for estimating total bacterial counts in ground beef. Minimum sensitivity was found to be 10⁶ cfu/g using a double filtration procedure for sample preparation. Although ATP content per cfu decreased approximately 10 fold during storage, correlation of total aerobic plate count (APC) with microbial ATP content was 0.96. Selective non-microbial ATP extraction with ATPase treatment was evaluated for use in conjunction with the double filtration procedure to increase assay sensitivity. The new method was effective for removing additional non-microbial ATP without reducing ATP in bacteria. Estimated APC values were generally accurate to within ±0.50 log for ground beef samples above the detection limit of 5 x 10⁴ cfu/g. ATPase treatment increased sensitivity of the ATP assay and APC estimation by about 1 log while increasing assay time by 40 minutes, for a total of 60 minutes for 4 samples assayed in triplicate. The ATP assay was evaluated for use with ground beef patties inoculated with mixed ground beef spoilage flora, <i>Pseudomonas</i>, or <i>Lactobacillus</i> and stored at 2°C or 10°C using oxygen permeable or impermeable (vacuum) packaging. Excellent correlation (r²=0.95) was obtained for each inoculum and storage condition over the range of 5 x 10⁴ to 1 x 10⁹ cfu/g, when estimated APC values were compared with experimentally observed APC values. Usefulness of the ATP assay for estimating APC values of frozen ground beef was evaluated. Retail ground beef and <i>Lactobacillus</i>- and <i>Pseudomonas</i>-inoculated beef were frozen and thawed at different rates and examined for APC and microbial ATP content. Results indicated that, although freezing and thawing lowered numbers of <i>Pseudomonas</i>, APC values and microbial ATP content closely correlated. APC estimates were generally accurate to within 1/2 log. The importance of using an ATP assay standard to correct for variable enzyme activity and presence of quenching factors was demonstrated, and improved formulae were developed for optimum assay standard use. Alternate regression methods were evaluated for estimation of APC values but did not yield enhanced accuracy. Only one regression equation was needed for estimating APC values of ground beef containing different types of bacteria stored in various ways. Therefore, little knowledge of ground beef history is needed in order to rapidly and accurately estimate microbial numbers in ground beef using the bioluminometric ATP assay. / Ph. D.

Thesis (M. Tech. ) - Central University of Technology, Free State, 2006 / Antibiotics have been used on animals since the Second World War for therapeutic purposes. The risks associated with the use of antibiotics in food animals are enormous, due to the possibility of resistance of organisms caused by the usage of low levels of antibiotics. The goals of this study were to determine the prevalence of antibiotic residues in C grade milk cows, and to determine the practices and knowledge of producers regarding the use of antibiotics as well as the knowledge and habits of consumers. In the study the presence of antibiotic residues was tested by means of microbiological inhibition testing. Fifteen percent of all tested samples tested positive for the presence of antibiotic residues. Eleven samples that tested positive on the microbiological inhibition test were sent to the Onderstepoort Veterinary Institute for confirmation. The knowledge of the consumer as well as that of the producer was tested by means of a questionnaire and then processed statistically. Producers were, in general, fairly ignorant regarding the withdrawal period of antibiotic residues. Age and the combination of age and reproduction were the common reasons for the selling of milk cows. Both the sampling and the questionnaires proved that the presence of antibiotic residues is higher than that stated in literature. The selling of the animals was mostly by auction or directly to the abattoirs. Consumer practices regarding the antibiotic residues were mostly in order, although consumers did not have knowledge regarding antibiotic residues. High temperatures, for example in the frying or grilling of meat, will reduce the presence of antibiotic residues because these effects have an influence on the presence of antibiotic residues (Rose et al., 1995). Almost 75% of consumers describe antibiotics in a positive manner. Milk and meat are regarded as posing the greatest risk for the origin of antibiotic residues. A lack of general knowledge regarding antibiotic residues was noteworthy, especially from the consumers of Thaba ’Nchu and Heidedal. The wrong usage of antibiotics by medical practitioners and consumers will certainly have consequences. Most of the consumers (112/227 respondents) indicated that they always completed a course of antibiotics. Forty-nine respondents indicated that they had already used antibiotics and that the therapy was unsuccessful. Antibiotic residues are still present so the risk to the consumer is still viable. Improved sampling and monitoring at abattoirs both for local and export abattoirs is necessary. The “farm to fork” concept and financial incentives by way of subsidies for residue-free products is a positive step. South African consumers are not quality conscious and further studies are necessary to improve the quality and safety of meat.