In this study, we focused on a mixture of mayonnaise and potato, known as "mayonnaise potato," which is sometimes used as a base material for potato salads sold in Japanese supermarkets. Five types of mayonnaise potato with different mayonnaise contents (weight percentage: 0%, 5%, 10%, 15%, and 20%) were prepared, the bacterial count was less than 10 CFU/g in each type. Then, potato salad was prepared by adding 5g of each ingredient (ham, cucumber, or both) to 100g of mayonnaise potato, and the standard plate count and coliform count were examined. The bacterial count of the potato salad with only ham was less than 10 CFU/g, regardless of the mayonnaise content. The bacterial count of the potato salad with only cucumber or ham and cucumber, and ≦10% mayonnaise content increased with the number of storage days, and the potato salad reached an almost putrefied state by the fifth day. The potato salad made with mayonnaise potato containing ≧15% mayonnaise (acetic acid content ≧0.076g/100g) exhibited consistent bacterial counts, irrespective of the ingredient type. Although ingredient-specific bacteria were detected, their numbers did not increase.
