Inactivation of Bacillus cereus spores in liquid food by combination treatments of heat and irradiation

Abstract

Spores of Bacillus cereus, like other bacterial spores, are heat and radiation resistance causing problem in food processing because of the high temperature or irradiation dose needed to inactivate them. In this work, combination treatments of heat and irradiation were tested for their potential to reduce heat-resistance of B. cereus spores in raw milk, carrot juice and water. D_T and Z-values were used to characterize heat resistance of these spores, whereas D₁₀-values were used to characterize radiation resistance. The results obtained indicated that D₈₅-values ranged from 24.9 to 35.2 min, D₉₀-values ranged from 7.6 to 11.6 min and D₉₅-values ranged from 2.4 to 4.7 min. The Z-values of B. cereus spores in the used media ranged from 9.81 to 11.24^oC. The D₁₀-values ranged from 1.9 to 2.6 kGy. Pre-irradiation treatment at 4 kGy followed by heating reduced D₉₀-values 2.8 to 3.4 times. The obtained findings indicated the effectiveness of irradiation at 4 kGy followed by heating in a same process to ensure safety of raw milk or carrot juice contaminated with Bacillus cereus. Key words: Bacillus cereus spores, heat resistance, radiation resistance.