Evaluation of the adequacy of the consume-by date of rice balls sold at convenience stores

The adequacy of the consume-by date was validated for rice balls sold at convenience stores (CVSs),taking into account the process of distribution. The results indicated that the increase in the viable cell counts differed significantly depending on the type of rice balls and the storage temperature. At 19 h after delivery, Staphylococcus spp. were detected in 4 samples (26.7%) of the Tunamayo samples of Company A and in the majority of the Plum samples of Company B. Results showed there was a strong correlation between the elapsed time after delivery and the viable cell counts for all samples except for the Plum samples of Company B. The regression equations varied for the different types of rice balls and the different storage temperatures. Using the obtained regression equations and assuming a safety factor of 0.7, the appropriate consume-by date was determined to be 11 h for the Tunamayo and 38 h for the Plum of Company A, and 21 h for the Tunamayo of Company B. Among 14 strains of isolated Gram-negative bacteria, 11 strains (78.6%) belonged to the genus Serratia.