Mesophilic and psychrotrophic aerobic sporulating microorganisms in raw cow’s milk

摘要

The occurrence of mesophilic and psychrotrophic aerobic sporulating microorganisms (MPAS) in raw cow's milk (RCM) and its relations to microflora in milk was studied. 294 samples of raw cow's milk in 14 farms were taken during one year.Basis of the method for MPAS assessment is to inactivate the milk sample at the temperature 80–82°C during 30 minutes and incubation in cultivation dishes at 30°C for 3 days – mesophilic aerobic sporulates (MAS), and at 7°C for 10 days – psychrotrophic aerobic sporulates (PAS). Results of studied microbiological parameters characterize the studied milk as complying with requirements of the EU regulation 92/46 and standard STN 57 0529. Mesophilic and psychrotrophic aerobic sporeforming microorganisms count (MPAS) was within the span 2.5–340 CFU/ml. Average value of MPAS was 59.4 CFU/ml, and variation coefficient 93.1 %. Count up to 50 CFU/ml was in 55.4% samples, in 85% was the value not higher than 100, and in 3.1% samples was the count of MPAS higher than 200. MPAS do not show correlation with any of the studied microbiological parameters; marked influences of season were not observed either. On the basis of obtained results it is possible to support the proposal of initial limit 200 CFU/ml as a maximum for the introduction of MPAS standard parameter.MPAS count found in the same dishes at incubation for mesophilic and subsequently strictly psychrophilic microorganisms (MAS+SPAS) was on average 56.9 CFU/ml, it represents 95.8 % out of the number of sums of individual dishes at two temperatures. Correlation coefficient of these two types of results r=0.99 gives evidence of close dependence that is expressed by linear regression equation y=0.9773x. Use of two incubation temperatures one after another with identical set of dishes enables to exclude overestimation of results with sporulates able to grow at both incubation temperatures