Psychrotrophic and thermoduric psychrotrophic microorganisms enumeration in milk: comparison of methods

Abstract

The aim of the present study was to evaluate whether the binomial temperature/time of 21 ºC for 25 hours, already validated for enumeration of psychrotrophics in milk, presents viability for enumeration of thermoduric psychrotrophic, comparing counts of psychrotrophic and psychrotrophic thermoduric obtained from each binomial of time and temperature of incubation. Twenty-eight refrigerated raw milk
samples collected in tank trucks in the reception platform of dairy industries in the northern of Paraná were evaluated. Psychrotrophic and thermoduric psychrotrophic were enumerated at 7 °C for 10 days and at 21 °C for 25 hours. For psychrotrophic, it was observed that there was no significant difference of the counts comparing the two methods of incubation (p = 0.46), the correlation coefficient between methods was 0.90 and the linear regression considered satisfactory. For thermoduric psychrotrophic it was not observed significant difference (p = 0.17) in the counts, however, the correlation coefficient between the two methods was 0.69 and the linear regression unsatisfactory. It was also observed greater homogeneity in the distribution of the psychrotrophic counts results towards thermoduric  psychrotrophic. The results demonstrate that the numeration of thermoduric psychrotrophic microorganisms by the faster methodology can change the result of the counts, since the coefficient of correlation and linear regression methods are low.