GERMINATION AND SUBSEQUENT INACTIVATION OFBACILLUS SUBTILISSPORES BY PULSED ELECTRIC FIELD TREATMENT

Abstract

The use of high‐intensity pulsed electric field (PEF) as a nonthermal method for triggering spore germination was investigated. Spores suspended in 0.01% NaCl solution (ca. 108cells/mL) were treated with an exponential‐decay pulse (20–50 kV/cm) at selected temperatures. The inactivation resulting from the direct effect of PEF treatment was less than 0.5 log cycles, even with a relatively high electric field intensity of 40 kV/cm. Most of the surviving PEF‐treated spores germinated after inoculation into selected germination media (0.85% NaCl solution, nutrient broth [NB], or tryptic soy broth [TSB]) and subsequent incubation at 37C for 40 min. The extent of germination increased with the treatment temperature and electric field intensity. More than 98% of surviving spores in TSB germinated during incubation after PEF treatment with an electric field strength of 40 kV/cm for 1,000 µs at 50C. The rate of germination in nutrient‐rich TSB medium was higher than that in NB. PRACTICAL APPLICATIONS High‐intensity pulsed electric field (PEF) treatments have been studied recently as an alternative method of conventional thermal sterilization. High‐intensity PEF inactivation of microorganisms can be carried out at ambient temperature with a short treatment time of seconds or less without inducing a significant temperature increase. Considerable research has been conducted on the inactivation of microbial cells using PEF. However, a major obstacle to the application of PEF as a technology for the preservation of foods and pharmaceuticals is that it is inefficient at inactivating bacterial spores. Bacterial spores are also resistant to inactivation by adverse physical and chemical agents. Methods to overcome this problem have been studied extensively with the aim of establishing reliable sterilization procedures for the food and pharmaceutical industries.

Microbiological evaluation of whole, sliced, and freeze‐dried black truffles (Tuber melanosporum) under vacuum packaging and refrigerator storage

“…The prevalence of this bacterial species in a wide range of food items such as pasta, rice, meat, eggs, and milk has also been reported. 64,65 According to the previous literature, counts more than 5 log CFU/g of Bacillus cereus in food are required to produce sufficient emetic toxin to cause disease. 66,67 Based on the results from this study, it suggests that the risk of foodborne illness caused by truffles is low due to the low Bacillus species counts.…”

Bacillus Spores in the Food Industry: A Review on Resistance and Response to Novel Inactivation Technologies

“…Up to a 3.5‐log reduction of B. cereus vegetative cells in skim milk, and a 3.1‐log reduction in skim milk with liquid egg white, was reported when field strength of 35 kV/cm for 200 Hz was applied and the temperature was maintained at 20 °C (Pina‐Pérez and others ). On the other hand, PEF when used as the only treatment for inactivation of Bacillus spores has been reported to be insufficient for a significant reduction in numbers (Hamilton and Sale ; Shin and others ). A reason for the variable results for the inactivation of spores could be due to variable germination.…”

Applications of green technologies‐based approaches for food safety enhancement: A comprehensive review

“…However, the process by which PEFs inactivate spores is unknown. PEFs, according to some researchers, can cause spore germination (Shin et al., 2010 ).…”