Survival and growth of Salmonella in reconstituted infant cereal hydrated with water, milk or apple juice and stored at 4°C, 15°C and 25°C

Abstract

Salmonella has caused foodborne illness through consumption of a variety of foods, including dry cereal and infant foods. In particular, reconstituted infant cereals may support growth of recovering or cross-contaminating Salmonella, especially if consumption is delayed and the meal is temperature abused. The objective of this study was to assess survival/growth of Salmonella inoculated (four-strain mixture) in rice, oatmeal, and mixed rice–oatmeal–wheat infant cereal, hydrated (0.5/3.0, w/v) with apple juice, pasteurized milk (2% fat) or water. The inoculated products were stored at 4°C, 15°C, or 25°C for 0, 8 and 24 h to simulate advance home preparation and abuse. Samples were analyzed by plating on tryptic soy agar with 0.6% yeast extract (TSAYE) and on XLT4 agar. There was no growth, but also no death, of Salmonella in any hydrated cereal stored at 4°C for 24 h. However, at 15°C Salmonella increased in cereals hydrated with water or milk from 1.6–2.3 log cfu ml −1 at time 0–4.1 to 5.4 log cfu ml −1 in 24 h, while at 25°C the pathogen reached 7.1–7.9 log cfu ml −1 in 24 h. However, in cereals hydrated with apple juice, growth of Salmonella was restricted (1.5–2.9 log cfu ml −1) after 24 h at 25°C, while weak or no growth occurred at 15°C. When hydrated with apple juice, rice cereal was less supportive of Salmonella growth compared to oatmeal and mixed cereals at 15°C and 25°C. Changes in Salmonella populations at 8 h of storage had similar patterns, with average increases being smaller compared with those at 24 h. Changes in bacterial populations on TSAYE followed trends similar to those on XLT4. These results indicate that hydrated infant cereal should be consumed immediately after preparation or held at 4°C for less than 8 h.