EFFECTS OF PHOSPHATE AND SODIUM AND POTASSIUM CHLORIDES ON SPORULATION AND HEAT RESISTANCE OF BACILLUS CEREUS

Abstract

ABSTRACT The effects of the addition of sodium and potassium chlorides and phosphate (sodium phosphate di‐basic/potassium phosphate monobasic) up to 0.25 mol/L in the sporulation medium on the percentages of sporulation and heat resistance of Bacillus cereus (ATCC 7004, 4342, 9818) were investigated. In all cases the sporulation rates varied between 85–95%, except for the ATCC 4342 strain when sodium and potassium chlorides were added at the highest level obtaining a 40 and 70% sporulation, respectively. Neither NaCl nor KCl had any significant effect on the heat resistance of the spores produced, obtaining D100 values of 0.04 ± 0.01, 0.31 ± 0.03 and 7.5 ± 0.4 min for strains 7004, 4342 and 9818, respectively. In all cases, as phosphate concentrations increased, decimal reduction times obtained gradually increased. However, the magnitude of the increase was dependent on the strain tested. While the strain 9818 exhibited about a 1.5‐fold increase in D103 values, the 4342 and 7004 strains showed D100 values that were about 6‐fold higher. No statistical significant differences were detected in z values, obtaining mean values of 7.3, 8.2 and 9.3C for 7004, 4342 and 9818 strains, respectively.PRACTICAL APPLICATIONSIn this article the thermal characteristics of three strains of Bacillus cereus with different sensitivity to heat produced in media with different content of phosphate (sodium phosphate dibasic/potassium phosphate dibasic) and sodium and potassium chlorides were evaluated. Data obtained showed that the supplementation of sporulation medium with phosphate allows for the development of B. cereus spores with increased heat resistance. These results have a great practical significance and could help to explain the presence of this microorganism in some heated foods.