Incidence of psychrotrophic lipolytic bacteria in cow's raw milk
2009
Cempirkova, R.,Jihoceska Univ., Ceske Budejovice (Czech Republic). Zemedelska Fakulta | Mikulova, M.,Jihoceska Univ., Ceske Budejovice (Czech Republic). Zemedelska Fakulta
The contamination of bulk samples of cow's raw milk (n = 491) by psychrotrophic lipolytic bacteria (PLiBC), total count of psychrotrophic bacteria (PBC) and mesophilic bacteria (TBC) was monitored for two years on eight dairy farms and the correlations among these groups of bacteria were analysed. An increase in TBC, PBC and PLiBC and in the values of free fatty acids (FFA) was tested experimentally in three milk samples in relation to time (analyses were done in 24-hour intervals until 96 hours) and storage temperature of milk samples (4; 6.5 and 10 deg C). Bacterial contamination of milk was determined by culture methods, the values of FFA were determined by an extraction-titration method. The following mean values were determined in 491 samples: PLiBC 659 CFU/mL, PBC 2,932 CFU/mL and TBC 18,932 CFU/mL. A high correlation was proved between PBC and PLiBC values (r = 0.87; P less than 0.001) while the correlation between TBC and PBC (r = 0.65; P less than 0.001), and between PLiBC and TBC (r = 0.59; P less than 0.001) was on a medium level. The proportional index pI for PLiBC/PBC was 0.20, for PLiBC/TBC 0.03 and for PBC/TBC 0.16. There was a significant difference between the increased values of TBC in summer in comparison with winter and spring. At 4 and 6.5 deg C TBC did not exceed the hygienic limit value (100,000 CFU/mL) even after 96 hours while it amounted to 90,000 CFU/mL after 48 hours at 10 deg C. The limit for TBC was exceeded several times after 96 hours at 10 deg C. PBC did not exceed the hygienic limit value (50,000 CFU/mL) even after 96 hours of storage at 4 deg C, but the values were 6 and 20 times higher than the hygienic limit after 72 hours at 6.5 deg C and after 48 hours at 10 deg C, respectively. A similar trend was observed in PLiBC which exceeded the limit value (43,000 CFU/ml) after 96 hours at 6.5 deg C and after 48 hours at 10 deg C, whereas at 4 deg C the limit value was not exceeded even after 96 hours. The content of FFA also increased in relation to the storage time and temperature.
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