Sterilization of Bacillus subtilis in Powdered Food by Iterative Processing of Instantaneous High-Pressure

Abstract

Powdered foods, primarily made from cereal grains, carry a high risk of contamination by soil bacteria at the time of harvest. However, due to the low thermal conductivity of powdered food and the spore-forming nature of soil bacteria, thermal sterilization is challenging. Currently, iterative processing with instantaneous high pressure generated by shock waves is a promising method for destroying bacterial cells without heat. In this study, rice flour, inoculated with Bacillus subtilis spores, was processed iteratively using instantaneous high pressure. The processing conditions were examined based on the number of iterations. The cultivation of B. subtilis and the observation of the cells by scanning electron microscopy were used as the evaluation method. As a result, 99.5% inactivation of B. subtilis was achieved. Additionally, deformed bacterial bodies and bacterial aggregation were observed. Therefore, the iterative processing using instantaneous high pressure can ensure the safety and security of powdered food.