The effects of temperature regimes on the microbiological safety and biochemical parameters of frozen beef over long-term storage periods

To guarantee the safety and high quality of meat and meat products, freezing is currently considered one of the most effective methods of preservation, commonly used in food industry. The objective of the study was to determine the activity of microbiota and the biochemical changes in frozen beef stored at different temperatures in order to substantiate optimal regimes that ensure high quality and safety of the raw material. Three regimes of storage were studied: –12 °С for 8 months, –20 °С for 14 months, and at –25 °С for 18 months. The microbiological analysis revealed that at –12 °С, a large amount of psychrotrophic microflora remained vital, whereas the number of fungi and yeasts even increased by 1.86 times. Storage at –20 °С reduced the levels of Enterobacteriaceae (on average by 20 times), mesophilic , and psychrotrophic microorganisms, and also stopped the reproduction of fungal microflora . At –25 °С, the results were similar to those at –20 °С, indicating absence of additional advantages of this regime in terms of microbiological stabi l ity. The biochemical studies revealed that at –12 °С, protein breakdown and hydrolysis of fats was more intensive, a c companied by the increases in the contents of amino-ammonia nitrogen (1.38 times) and volatile fatty acids (4.63 times), compared with fresh meat, and also an increase in рН up to 6.05 ± 0.03. Such changes indicate the formation of signs of ‘doubtful freshness’. At –20 °С and –25 °С, those parameters changed insignificantly, allowing the meat to be classified as fresh. The analysis of lipid peroxidation indicated that an increase in the temperature of storage promoted a more intensive formation of TBA-active products and diene conjugates. At –12 °С, their contents increased by 13.0 ± 0.2% and 27.2 ± 0.3%, respectively, while no statistically significant changes were observed at –20 °С and –25 °С. The yiel d ed results indicate that an optimal regime for long (over 12 months) storage of beef is –20 °С, which provided a high level of microbiological safety, slowed down the course of unsatisfactory biochemical processes, without any additional energy expenditures required for the –25 °С regime. The –12 °С regime can be used only for short-term storage given a low initial contamination and control of the development of fungal microflora .