Mechanisms and efficacy of wet heat, dry heat, and steam-based treatments for bacterial spore inactivation

Dry and wet heat treatments are widely used physical methods for microbial inactivation, and their effectiveness in destroying bacterial spores has been extensively demonstrated. This review systematically discusses the bactericidal effects and underlying mechanisms of dry heat, wet heat, and steam-based treatments on bacterial spores. Wet heat inactivates spores through heat-induced protein denaturation and dipicolinic acid release, resulting in multi-level structural damage, including spore coat collapse, cortical peptidoglycan hydrolysis, and core hydration. On the other hand, dry heat treatment requires the creation of a high-energy thermal environment (typically > 160°C), and its inactivation mechanism involves a dual pathway: spore dehydration and mechanical stress, along with damage to the DNA repair system, ultimately causing irreversible injury. Steam treatment overcomes limitations in traditional heat transfer. While saturated steam follows the mechanism of wet heat, pulsed superheated steam integrates both dry heat and wet heat inactivation mechanisms, significantly enhancing spore inactivation efficiency. Importantly, combining thermal treatments with the bactericidal agents can create synergistic effects, further improving sterilization efficacy. These technologies show great potential for application in the food industry. However, further research is needed to optimize processing parameters, reduce operational costs, and promote their commercial application.