The aim of this study was to analyze changes in the microbiological quality of Longissimus lumborum (LL) muscles collected from young Polish Holstein-Friesian Black-and-White (PHF BW) bulls and stored for 7, 14, and 21 days under different modified atmospheres (MA) (vacuum, 80% O2 + 20% CO2, 60% O2 + 30% CO2 + 10% N2, 40% CO2 + 60% N2, 30% CO2 + 70% Ar). Before and after the specified storage periods, crosssectional samples of the LL muscle were collected under aseptic conditions to determine total microbial counts, and the total counts of psychrotrophic bacteria and mesophilic lactic acid bacteria. The effects of storage time and MA composition on changes in the parameters analyzed were evaluated, and the effectiveness of argon in delaying microbial growth in cold-stored beef was determined. Between days 7 and 14 of storage, total microbial counts were lowest in meat packaged under the MA composed of 30% CO2 + 70% Ar, whereas between days 14 and 21 they were lowest in both MA packages containing O2. The greatest increase in total microbial counts between days 7 and 14 of storage was noted in the MAs containing O2, and between days 14 and 21 of storage in the MA containing Ar. Beef stored for 7 days in the MA containing 60% O2 was characterized by the lowest total microbial counts, whereas the highest total microbial counts were noted in samples stored for 14 days in the MA containing 80% O2. Between days 7 and 14 of storage, the counts of psychrotrophic bacteria increased significantly in all MAs. Between days 14 and 21 of storage, the counts of psychrotrophic bacteria did not increase in meat samples packaged under vacuum or the MA composed of 80% O2 + 20% CO2. The counts of psychrotrophs were significantly lower in beef stored for 7 days in the oxygen-free MAs than they were in both MA packages containing O2. The counts of psychrotrophic bacteria were significantly lower in beef stored for 14 days in the MA containing Ar, compared with samples packaged under vacuum and the MA containing 80% O2. Gas composition in MA packaging had no significant effect on total microbial counts or the counts of psychrotrophic bacteria in meat stored for 21 days. Between days 14 and 21 of storage, the counts of lactic acid bacteria did not increase significantly only in meat packaged in the MAs composed of 60% O2 + 30% CO2 + 10% N2 and 40% CO2 + 60% N2. After 7 days of storage, the counts of lactic acid bacteria were higher in beef packaged in oxygen-free MAs than they were in both MA packages containing O2. After 14 days of storage, the counts of lactic acid bacteria were higher in meat packaged in the MA composed of 80% O2 + 20% CO2 than they were in the other MAs. Beef samples stored for 21 days under the MA composed of 80% O2 + 20% CO2 were characterized by significantly lower counts of lactic acid bacteria, compared with samples stored under the other MAs, except for the MA composed of 40% CO2 + 60% N2. It can be concluded that beef can be stored in the MA composed of 30% CO2 + 70% Ar for shorter periods of time (up to 14 days). The modified atmosphere composed of 30% CO2 + 70% Ar contributed to slower microbial growth in meat and resulted in lower counts of psychrotrophs and lactic acid bacteria, relative to the other samples. However, there is a need for further research on different concentrations of argon in MA packages to confirm that this gas can effectively delay microbial growth in beef. Meat stored for 14 days in the MA composed of 80% O2 + 20% CO2 was characterized by the lowest microbiological quality. The composition of MAs had a minor influence on the growth rates of the microbial groups analyzed in beef stored for 21 days; certain changes were observed only in the counts of lactic acid bacteria.
ATP-Bioluminescence as a method to evaluated microbiological quality of UHT milk
