Contamination of frozen fish with mesophilic and psychrotrophic microorganisms depending on biochemical quality indices
AbstractBecause of the high nutritional and biological value, fish is a good nutrient for the development of all groups of microorganisms, making it a perishable kind of food. The conditions of fish storage require appropriate temperature regimes to stop the development of microorganisms. The purpose of the research is to investigate the bioassay of frozen mesophyll and psychrotrophic microflora, depending on the biochemical parameters which characterize its freshness. Mesophilic aerobic and elective anaerobic organisms in samples were found at a temperature of 30 ± 1 ºС within bioassay incubation for 72 hours and psychrotrophic microflora at a temperature of 6.5 ± 0.5 ºC within incubation for 10 days. Biochemical parameters include reaction with copper sulfate, peroxidase, total volatile base nitrogen and pH by generally accepted methods. It was discovered that frozen fish in reaction with copper sulfate, that was prior classified as fresh and benign, according to the content of mesophilic aerobic and elective anaerobic organisms, in of 25% of cases on average did not meet the microbiological standard of DSTU 4868:2007. At the same time, approximately 70% of samples of frozen fish which contained psychrotrophic microflora were found to be higher than established norm for mesophilic aerobic and elective anaerobic organisms, and 25.9 ± 1.4% of samples exceeded the number of 100.000 CFU/g. It was determined that for a positive reaction to peroxidase, the number of frozen fish samples complying with the microbiological standard according to the content of mesophilic aerobic and elective anaerobic organisms was 64.9 ± 2.7%, which is 1.6 times higher than in samples with such quantity of psychrotrophic microorganisms. The benign fish in response to peroxidase was contaminated with mesophilic microflora from 50.000 to 1 million CFU/g in 32,5 ± 1,3% of cases, and with psychrotrophic microflora 1,7 times more. This indicates a significant insemination of the fish microflora, which, based on the results of studies on peroxidase, is fresh. For a negative reaction to volatile base nitrogen, 30% of frozen fish samples, which were contaminated with mesophilic aerobic and elective anaerobic organisms, were found to have more than 50.000 CFU/g and 46.2% ± 1,8% of psychrotrophs. It was established that 48% of fish samples according to the content of mesophilic aerobic and elective anaerobic organisms and 57.6% by content of psychrotrophs did not meet the microbiological standard of DSTU 4868:2007 for the pH quality indicator in fresh fish. Consequently, the results of the research indicate that with satisfactory biochemical parameters of frozen fish in reaction with copper sulfate, peroxidase, the content of total volatile base nitrogen and pH, 25–50% of fish samples with over-normative (more than 50.000 CFU/g) content of mesophilic aerobic and elective anaerobic organisms. It was discovered that the psychrotrophic microflora is quantitatively predominant in the content of mesophilic aerobic and elective anaerobic organisms of frozen fish. In fish samples, which according to biochemical parameters are related to benign fresh, psychrotrophs exceeded the number of 50.000 CFU/g in 60–70% of cases.
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