Presence and Growth of Bacillus cereus in Dehydrated Potato Flakes and Hot-Held, Ready-to-Eat Potato Products Purchased in New Zealand

Abstract

Potato products prepared from dehydrated potato flakes have been implicated in foodborne illness incidents involving Bacillus cereus intoxications. B. cereus can survive as spores in potato flakes and can germinate and multiply in the rehydrated product. This study assessed the frequency and concentration of B. cereus in dehydrated potato flakes and hot-held, ready-toeat mashed potato products. Of 50 packets of potato flakes tested, eight contained greater than 100 CFU/g B. cereus (maximum 370 CFU/g). The temperature of the potato portion of 44 hot-held food products was measured immediately after purchase, and 86% were below the safe hot-holding temperature of 60°C. The potato portions were subsequently tested for B. cereus. Only two of the potato portions contained B. cereus at greater than 100 CFU/g, a potato-topped pastry (1,000 CFU/g) and a container of potato and gravy (120 CFU/g). To assess multiplication of B. cereus in this food, we held rehydrated potato flakes with naturally occurring B. cereus at 37, 42, and 50°C and tested them over 6 h. By 6 h, the number of B. cereus in potato stored at 37°C had exceeded 103 CFU/g, was greater than 104 CFU/g at 50°C, and was close to 106 CFU/g at 42°C. Growth data were compared to predictions from the U.S. Department of Agriculture Pathogen Modeling Program (PMP 7.0). The PMP predictions were found to simulate the measured growth better at 42°C than at 37°C. Hot-held potato products should be safe for consumption if held at 60°C or above or discarded within 2 h.