Revealing the mechanism of ohmic heating against Bacillus cereus spores through intracellular homeostasis and lipid analysis

Abstract

B. cereus spores can cause food spoilage, leading to food-borne illness and significant economic losses. Ohmic heating (OH) is an emerging and alternative thermal processing technique widely used for pasteurizing or sterilizing food, with the potential to inactivate spores. The results of this study indicated that OH can effectively inactivate B. cereus spores. To elucidate the inactivation mechanism of B. cereus spores by OH, several physicochemical indices were investigated, including spore characteristics, spore membrane integrity, intracellular substance concentration, and spore lipid composition. OH treatment neither produced H₂O₂ during processing nor caused lipid oxidation in spores. Both oil bath heating (OB) and OH treatments affected catalase, glutathione peroxidase, ATPase, Na⁺/K⁺-ATPase, and Ca²⁺/Mg²⁺-ATPase activity, suggesting a disruption in the intracellular homeostasis of the spores. Additionally, K⁺, Ca²⁺, and Mg²⁺ leakage from spores, and a decrease in inner membrane fluidity was observed following OB and OH treatments. However, OH treatment at 10 V/cm and 50 Hz resulted in minimal cation leakage and more pronounced catalase activity damage. OH treatments had a more significant impact on the lipid composition and metabolism pathways of spores than OB treatment, particularly concerning major membrane-forming phospholipids and glycerophospholipid metabolism. This study provides a comprehensive understanding of the OH inactivation mechanism on spores from various perspectives, promoting theoretical advancement of OH application in food sterilization.