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

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.

蜡样芽孢杆菌孢子可导致食物腐败，引发食源性疾病并造成重大经济损失。欧姆加热（OH）是一种新兴的替代热处理技术，广泛用于食品的巴氏杀菌或灭菌，具有使孢子失活的潜力。本研究结果表明，欧姆加热可有效使蜡样芽孢杆菌孢子失活。为阐明欧姆加热使蜡样芽孢杆菌孢子失活的机制，对若干理化指标进行了研究，包括孢子特性、孢子膜完整性、细胞内物质浓度以及孢子脂质组成。欧姆加热处理在过程中既不产生过氧化氢，也不会引起孢子中的脂质氧化。油浴加热（OB）和欧姆加热处理均影响过氧化氢酶、谷胱甘肽过氧化物酶、ATP酶、钠/钾 - ATP酶以及钙/镁 - ATP酶的活性，这表明孢子的细胞内稳态受到破坏。此外，在油浴加热和欧姆加热处理后，观察到孢子中的钾离子、钙离子和镁离子泄漏，以及内膜流动性降低。然而，在10伏/厘米和50赫兹的欧姆加热处理导致的阳离子泄漏最少，且对过氧化氢酶活性的损害更显著。与油浴加热处理相比，欧姆加热处理对孢子的脂质组成和代谢途径影响更显著，特别是在主要的成膜磷脂和甘油磷脂代谢方面。本研究从多个角度全面了解了欧姆加热对孢子的失活机制，促进了欧姆加热在食品灭菌中应用的理论进展。