Efficacy of sushi rice acidification: Quantification of Bacillus cereus and Clostridium perfringens during simulation of retail practices

Abstract

This study aimed to investigate the efficacy of sushi rice acidification on the growth of B. cereus and C. prefringens. The white sushi rice was cooked in a rice cooker, and the pH was adjusted with rice vinegar to 4.2 ± 0.05 or 4.6 ± 0.05 to compare pH recommended by the U.S. Food Code and lower pH used by sushi retails. The rice was inoculated with C. perfringens, and B. cereus to a final count of 104 CFU/g and was held at room-temperature (23 ± 1) or 37.7 ± 1 °C. Three samples were taken at time zero, 12, and 24 h post-inoculation and plated on selective media for pathogens quantification. The means and S.D. of B. cereus and C. perfringens at time zero were 3.4 ± 0.2 and 3.0 ± 0.2 log CFU/g respectively. No recovery of C. perfringens and B. cereus was found at time 12 or 24 h when held at room-temperature at pH 4.2 ± 0.05, while B. cereus were survived pH 4.6 ± 0.05 at both storage times. However, both pathogens were significantly recovered when held at 37.7 ± 1 °C at pH 4.2 ± 0.05 and 4.6 ± 0.05. These results demonstrate that acidified white rice with a pH 4.2 inhibits the growth C. perfringens and B. cereus at room-temperature for up to 24 h.