The effect of psychrotrophic bacteria in pasteurized milk during storage
1987
Nichas, E.G. | Samaras, F. (Ministry of Agriculture, Lycovrissi-Attici (Greece). Food Technology Inst.)
The microbiological and the physico-chemical changes of pasteurized milk during storage at 3-4 deg C, were studied. It was established that a microbial association of Lactic acid bacteria, yeasts, Pseudomonas spp. and Enterobacteriaceae existed in all samples. The initial proportion of the above mentioned microorganisms was 47.54%, 39.53%, 10.33% and 2.58%, respectively. It was observed that the Pseudomonas spp. markedly increased their propotion during storage at 3-4 deg C. Their final contribution (29.68%) to the microbial flora in pasteurized milk was at the same level with these of Lastic acid bacteria (29.77%) and yeasts (29.49%) at the very end of storage. An increase of 10% TCA-soluble proteins (peptides and/or free amino acids) did also occurred. The inoculation of long-life milk with Citrobacter freundii or Pseudomonas spp. showed that an increase in the amount of soluble nitrogen substances in 10% TCA was associated only with the presence of Pseudomonas sp. The gluconate production was also attributed to the activity of pseudomonads, organisms which grew extensively in milk. The rate of build up and the extent of gluconate production was found to be influenced by the temperature
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