Heat resistance of Bacillus cereus spores in carrot extract acidified with different acidulants B. Moussa-Boudjemaa a , J. Gonzalez b , M. Lopez b, * a Department of Biology, Faculty of Science, University of Tlemcen, Algeria b Higiene y Tecnologı ´a de los Alimentos, Facultad de Veterinaria, Universidad de Leo ´ n, Campus de Vegazana s/n. 24071 Leo ´ n, Spain Received 16 October 2004; received in revised form 15 May 2005; accepted 17 May 2005 Abstract 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. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Bacillus cereus spores; Heat resistance; Food safety; Acidity; pH 1. Introduction Bacillus cereus is a recognized food-borne bacterium causing illness which accounts for a significant percent- age of reported food-borne diseases with known aetiol- ogy (Gasaluk, Yokoyama, Kimura, & Sugihara, 1996; Pan, Wang, Lee, Chien, & Hong, 1997; Shinagawa, 1993). However, the number of cases is likely to be underestimated as a consequence of the short duration and relative mildness of the illness (Duynhoven & Wit, 1997; Granum, 1997). B. cereus has been reported as one of the psychro- trophic micro-organisms most commonly isolated from pasteurized and sous vide foods (Carlin et al., 2000; Crielly, Logan, & Anderton, 1994; Harmon & Kautter, 1991) and occasionally from UHT and sterilized foods (Bradshaw, Peeler, & Twedt, 1975; Franklin, 1970; Mostert, Lu ¨ck, & Husmann, 1979). To ensure the safety of these products with respect to B. cereus it is essential to understand factors affecting the heat resis- tance of its spores. It has been observed that the sub- culture temperature and the composition and pH of the recovery medium, as well as the presence of some approved food additives, have a substantial influence over germination, development and apparent thermal resistance of injured B. cereus spores (Gonza ´lez, Lo ´ pez, Mazas, Bernardo, & Martin, 1996; Gonza ´lez, Lo ´ pez, Mazas, Bernardo, & Martin, 1997; Gonza ´lez, Lo ´ pez, Mazas, Gonza ´lez, & Bernardo, 1995). The com- position and pH of the heating medium are also consid- ered as further factors with a strong influence on the thermal inactivation of this micro-organism (Faille, Lebret, Gavini, & Maingonnat, 1997; Mazas et al., 0956-7135/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2005.05.009 * Corresponding author. Tel.: +34 87 291183; fax: +34 87 291284. E-mail address: dhtmlf@unileon.es (M. Lopez). www.elsevier.com/locate/foodcont Food Control 17 (2006) 819–824