Mechanisms of low energy electron beam and isostatic high pressure processing as non-thermal spore control strategies

Abstract

Bacterial spores pose the largest hurdle for the preservation of perishable food due to their extreme resistance to processing steps. Conventionally, food industries apply intensive decontamination processing steps, most commonly thermal processing, to inactivate bacterial spores. However, this is not suitable for heat-sensitive products, ingredients, and materials. Moreover, the high thermal load of treated products often leads to reduced quality concerning their organoleptic and nutritional attributes. To meet consumer needs of fresher, minimally processed food products, food industries and scientists have been searching for novel non-thermal, mild but efficient spore control strategies. Among the emerging decontamination technologies, low energy electron beam (LEEB) and high pressure (HP) technologies have shown high potential because of the reduced thermal-load and improved quality retention of the treated foods. Therefore, in this research, these two non-thermal processing technologies were investigated for their spore inactivation efficiency and mechanisms. The results revealed that the inactivation efficiency of LEEB technology was in a comparable range to that of the other ionizing irradiation technologies and was influenced by various factors, including spore species and sporulation conditions. The mechanistic study revealed that DNA damage was one of the causes of spore inactivation by LEEB and the investigation of a newly developed continuous industrial LEEB system demonstrated a high potential to upscale LEEB processing for the decontamination of low water activity food surfaces (e.g. for spices). HP can inactivate bacterial spores by first triggering germination. The key limitation for the application of HP-based germination-inactivation approaches is that spore germination is extremely heterogeneous under HP. This research optimized and thoroughly validated the use of flow cytometry to study spore germination behavior under HP. Results revealed four distinct responses of spores under HP treatment at 150 MPa and 37°C. A protocol based on fluorescence-activated cell sorting was further developed to isolate spores of different physiological states after HP treatment. The methods developed in this study provide a foundation for future research on spore inactivation using LEEB and heterogeneous spore behavior upon HP treatment. The outcome can further help the development and implementation of LEEB and HP technologies as non-thermal, gentle spore control approaches, which will help deliver safe and minimally processed foods to consumers in the future.