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

Abstract

Abstract We studied the occurrence of mesophilic and psychrotrophic aerobic sporulating microorganisms (MPAS) in raw cow’s milk and their relations to microflora in milk. We took 294 samples of raw cow’s milk from 14 farms during one year. Briefly the method for MPAS assessment is to inactivate the milk sample by heating it to 80-82°C for 30 minutes. Mesophilic aerobic sporulates are incubated at 30°C for 3 days-, and psychrotrophic aerobic sporulates at 7°C for 10 days. Results of studied microbiological parameters characterize the sampled milk as complying with requirements of the EU regulation 92/46 and standard STN 57 0529. MPAS count was within the span 2.5–340 CFU/ml. The average value ofMPAS was 59.4 CFU/ml, with variation coefficient 93.1%. Counts up to 50 CFU/ml were in 55.4% samples, the value was not higher than 100 in 85%, and in 3.1% of the samples the MPAS count was 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 an initial limit of maximum 200 CFU/ml for the introduction of a MPAS parameter. MPAS count found in the same dishes at incubation for mesophilic and subsequently strictly psychrophilic microorganisms was 56.9 CFU/ml on average. This represents 95.8% of total CFU sums of individual dishes at two temperatures. The correlation coefficient of these two types of results, r = 0.99,gives evidence of close dependence expressed by the linear regression equation. Use of two incubation temperatures, one after another with an identical set of dishes, enables us to exclude overestimation of results due to sporulates able to grow at both incubation temperatures.