Each of fifteen samples of rice-ball and sandwiches from fifteen convenience stores of three different companies was examined for viable bacterial counts, that is coliform group and Staphylococcus aureus immediately after the purchase and on the day of expiration. The viable bacterial counts among the rice-balls with salmon and egg sandwiches at 45 convenience stores showed agreat variation although the stores obtained the products from the same manufacturers.
In most samples, there was no problem concerning taste 24 hours after the purchase, but the viable bacterial count after purchase and on the day of expiration was over 105 cfu/g in 22% of the samples.
The values of coliform groups after the purchase were less at store C than those at stores A and B, and the count of organisms on the day of expiration was the least at store B.
In the test of preservation, the concentration of viable bacterial counts in the foods did not change at 15°C for 25 hours, but increased to 106 cfu/g at 25°C.
Growth and enterotoxin A production of Staphylococcus aureus at 25°C for 24 hours showed counts of 107 cfu/g and 40 ng/g in boiled egg, and 108 cfu/g and 20 ng/g in rice, respectively. Staphylococcus aureus was isolated with a count of 102 cfu/g from only one sample of egg sandwiches at store C.
