Study on the effect of freezing on the changes of chemical and microbial quality of butter

Freezing causes changes on chemical and microbial quality of butter. In this research, effects of two different temperatures -9 and -18^oC on changes of moisture, fat, acidity and peroxide value and also Coliform and Psychrotrophic microorganisms in frozen butter were studied. Results showed that values of moisture and fat during 7 months of frozen storage at two temperatures decreased 1.8% and increased 1.78%, respectively. Acidity and peroxide value during 7 months of storage at two temperatures had no significant difference changes (P<0.05). Coliform microorganisms were destroyed after 2 months of freezing and the numbers of cells became zero. The numbers of Physchrotrophic microorganisms did not out of the range of standard in all and at -18^oC in compare to -9 ^oC was decreased more. Effects of storage temperatures and different weights on the chemical and microbial quality of butter were not significant (P<0.05).