Reduction of Bacillus cereus spores in sikhye, a traditional Korean rice beverage, by modified tyndallization processes with and without carbon dioxide injection

AIMS: The objective of this study was to inactivate Bacillus cereus spores in sikhye using a modified tyndallization process involving injection with carbon dioxide (CO₂). METHODS AND RESULTS: Heat tolerance of B. cereus spores in tryptic soy broth and sikhye was evaluated. The D(95°C) values of the B. cereus spores were 2·8-4·9 min, dependent of type of heating medium or inoculum level. The lethality of conventional heat treatment and modified tyndallization with or without CO₂ injection against B. cereus spores in sikhye was determined. The order of effectiveness was modified tyndallization with CO₂ > modified tyndallization without CO₂ > conventional heat treatment. Modified tyndallization with CO₂ reduced the number of B. cereus spores in sikhye by 5·8 log CFU ml⁻¹. The increased CO₂ concentration and decreased pH of sikhye resulting from CO₂ injection rapidly reverted to near-normal values after heat treatment. CONCLUSIONS: Modified tyndallization with CO₂ was more effective than conventional heat treatment or modified tyndallization without CO₂ in reducing B. cereus spores in sikhye. SIGNIFICANCE AND IMPACT OF THE STUDY: Results of this study will be useful when developing strategies to control B. cereus spores in sikhye and may have application to other beverages.