Safety and pH measurements of sushi rice in Japanese restaurants in Burnaby BC, Canada

Abstract

Background and Purpose: The increasing popularity of sushi in Metro Vancouver raises public health concerns over the consumption of sushi rice being held out of temperature control. Although sushi rice is acidified to control growth of pathogenic microorganisms, there is no existing documented system to monitor the pH of sushi rice, and pH testing is rarely performed by Environmental Health Officers(EHOs)/Public Health Inspectors(PHIs) during routine inspections. The purpose of the study was to measure the pH of sushi rice samples collected from different sushi restaurants in Burnaby, BC and determine whether the pH meets the accepted standard of 4.6 or below. Methods: 30 sushi rice samples were collected from 30 randomly selected sushi restaurants in Burnaby, British Columbia. The samples were kept at room temperature and then tested for pH using the Waterproof Palm pH Meter. Results: The mean pH of the samples was 4.09; the median was 4.115; the standard deviation was 0.198; and the range was 0.82 with the minimum value of 3.71 and the maximum value of 4.53. 100% (30 out of 30 samples) had the pH less than 4.6. The statistical z-test resulted in a p-value of 0.00. Discussion: All of the sushi rice samples had pH values less than 4.6. Therefore, the samples were adequately acidified to inhibit the growth of pathogens. The low pH values indicate that the samples are not considered potentially hazardous food, thus safe to be stored at room temperature for extended periods of time. However, due to the nature of Bacillus cereus that can grow at a pH 4.3 or higher, the target pH of sushi rice is 4.3 or lower. Conclusion: Inadequately acidified sushi rice may pose a health risk if it is stored out of temperature control. The study shows that sushi rice being consumed by the public in Burnaby, BC is generally safe and has a low public health concern. Therefore, EHOs/PHIs can feel assured that sushi rice stored at room temperature is unlikely to cause potential foodborne illness.