Influence of pH and temperature on growth of Bacillus cereus in vegetable substrates

Bacillus cereus is a food-borne pathogen which most often contaminates foods of plant origin. Spores of psychrotrophic strains have the ability to germinate and grow at refrigeration temperatures in different vegetable substrates, such as carrot broth, zucchini broth, and cooked carrot purée. In some circumstances, factors such as pH, heat treatment, and storage temperature play a fundamental role in controlling the growth of these psychrotrophic strains and in extending the shelf life of refrigerated, minimally processed vegetable-based products in relation to pathogenic spore-forming bacteria. The combination of mild acidification (pH 5.0) and refrigeration (≤8 °C) inhibited B. cereus growth for at least 60 days in vegetable substrates similar to those mentioned above. This protection was maintained even when the temperature to which the food was exposed reached 12 °C. Psychrotrophic strains of B. cereus were inhibited in carrot broth by heating at 90 °C for 7.5 min, if the broth was refrigerated at a temperature of 8 °C or lower. If the vegetable product was exposed to temperatures of mild abuse (12 °C), it was necessary to implement a more drastic heat treatment (90 °C for 30 min).