抄録
Sixty-two samples of bottled milk collected from milk plants and food stores were examined for contamination with psychrophilic and mesophilic bacteria and changes in quality during storage.
1. Of 38 samples collected from milk plants, twenty-four were contaminated with less than 30 psychrophilic organisms per sample. After storage at 5×7°C for 7 days, more than 106psychrophilic organisms were found in each of 35 samples. The situation was similar in the case of mesophilic organism situation was similar in the case of mesophilic organisms.
2. The psychrophilic-bacterial count was arranged as less than 30 (10 samples), 104, 101, 103, and 102in the decreasing order in 24 samples of commercial bottled milk. The mesophilic-bacterial count was a little lower than it.
3. Acidity was about 0.13 per cent immediately after collection. After storage at low temperature milk-plant samples still remained within the standard of acidity, but 15 samples of commercial milk failed to meet this standard. Only two of them showed coagulation.
4. Results were almost identical between the boiling and the alcohol tests. After storage at low temperature, about 70 per cent of commercial milk samples were positive for both tests.
5. Flavor was altered in almost all samples after storage at low temperature. Most samples became rancid.
6. Ability of protein decomposition was revealed by 50 and 30 per cent of the isolated psychrophilic and mesophilic bacteria, respectively, and ability of fat decomposition by 19 and 8 per cent.
7. Pseudomonas was predominant among the psychrophilic and mesophilic bacteria isolated. After storage, Pseudomonas was predominant among the psychrophilic bacteria isolated, but one of Enterobacteriaceae, Streptococcus, asporogenous Grampositive rods, and Micrococcus prevailed among the mesophilic bacteria isolated in most cases.
8. These results indicate that the contamination of bottled milk with psychrophilic bacteria cannot be neglected from the viewpoint of food sanitation.
