Survival and growth of Listeria species in a model ready-to-use vegetable product containing raw and cooked ingredients as affected by storage temperature and acidification

The survival and growth of Listeria monocytogenes and L. innocua strains in oculated onto cooked sweet corn and fresh bean sprouts packed individually, and as components of a combination product, were examined at refrigeration and mild abuse temperatures. Growth rates were both temperature and vegeta ble dependent. Maximal growth rates (1.14 +/- 0.11og CFU/day) were identifi ed on cooked sweet corn at 12 degrees C. The inclusion of cooked sweet corn did not significantly increase (P > 0.05) the growth rate or final Listeri a population density of bean sprouts stored at 8 degrees C and 12 degrees C . The sensory quality of bean sprouts was relatively temperature independen t for the initial 48 h of storage, but was maximized (4 days shelf life) at 3 degrees C. Acidification of sweet corn to pH 5, particularly with citric acid, slowed Listeria growth and could be an additional hurdle to suppleme nt temperature in maintaining the safety of minimally processed vegetable c ombination products.