Heat resistance of Bacillus cereus spores in carrot extract acidified with different acidulants

The effect of acidification of carrot extract on the heat resistance of Bacillus cereus (ATCC 7004 and 4342) spores was studied. Malic, acetic, citric, ascorbic, lactic and hydrochloric acids were used as acidulants. Thermal resistance experiments were performed over the range 82–108 °C with continuous monitoring of pH. Non-acidified carrot extract (pH 5.2) had a protective effect on the thermal inactivation of spores when compared with the reference McIlvaine buffer at the same pH value. Acidification of carrot extract reduced the D-values obtained for spores, this effect occurring whatever the type of acidulant used. For both strains and all treatment temperatures, as pH decreased the D-values decreased exponentially over the pH range studied (5.2–4.0), yielding straight lines, basically parallel, with an average slope of 0.203 ± 0.023. Significant decreases in survivor counts and apparent D-values were observed when injured spores were recovered using the usual recovery medium containing carrot extract.