Incidence and growth potential of Bacillus cereus in ready-to-serve foods

Abstract

To simulate temperature abuse, 106 test portions of ready-to-serve moist foods, 12 test portions of rehydrated powdered infant formula, and 18 test portions of nonfat dry milk were incubated for 20 and 24 h at 26°C, and then examined for Bacillus cereus. Of the ready-to-serve moist foods, 88 of 106 were positive for B. cereus at levels ranging from 0.25 to 8.5 × 106/g after 20 h of incubation and from 0.1 to 58 × 106/g after 24 h. All of the powdered milk and 12 of the 15 units of infant formula, representing five brands, were positive, with counts ranging from 0.15 to 5.0 × 106/g in 20 h and 5.0 to 49 × 106 after 24 h. B. cereus counts in the powdered products were low, ranging from 0.09/g for one of two soy-based products to an average of 0.29/g for milk-based products. However, these levels were sufficient to initiate growth of B. cereus in almost every 2-oz serving. Similar results were obtained for rehydrated nonfat milk, with initial B. cereus counts ranging from 0.29 to 1.5/g; at 26°C the counts averaged 3.3 × 107 after 20 h and 5.5 × 107 after 24 h. Counts ranged from 2.0 × 104 to 1.1 × 105 after 9 h in milk and were in excess of 106/g after 10.5 h.