THERMODESTRUCTION OF BACILLUS SPORES IN MILK1

Abstract

The rate of heat destruction of spores of 12 selected strains of Bacillus species was determined in skimmilk. Bacillus cereus and Bacillus licheniformis, the most prevalent Bacillus species in raw milk, were most heat resistant. The D values at 100 C ranged from 0.875 min for Bacillus pumilus to 4.10 min for B. licheniformis A-5. Extremes for Z values were 6.4 C for B. licheniformis A-1 and 11.5 C for Bacillus circulans. For each of the spores studied, linear regression equations with standard error are presented for the thermal destruction process at 95, 97.5, and 100 C. Heat resistance of bacillus spores in milk varied between the strains studied and the heating conditions imposed.