Heat Resistance of Bacillus cereus Spores: Effects of Milk Constituents and Stabilizing Additives

Abstract

Heat resistance of Bacillus cereus spores (ATCC 7004, 4342, and 9818) heated in different types of milk (skim, whole, and concentrated skim milk), skim milk containing stabilizing additives (sodium citrate, monopotassium phosphate, or disodium phosphate, 0.1%), and cream was investigated. Thermal resistance experiments were performed at temperatures within the range of 92 to 115 degrees C under continuous monitoring of pH. For strain 4342 no significant differences (P < 0.05) in D values were detected in any case. For strains 7004 and 9818 higher D values of about 20% were obtained in whole and concentrated skim milk than those calculated in skim milk. From all stabilizing additives tested, only sodium citrate and sodium phosphate increased the heat resistance for strain 9818. However, when the menstruum pH was measured at the treatment temperature, different pH values were found between the heating media. The differences in heat resistance observed could be due to a pH effect rather than to the difference in the substrates in which spores were heated. In contrast, when cream (fat content 20%) was used, lower D values were obtained, especially for strains 7004 and 9818. z values were not significantly modified by the milk composition, with an average z value of 7.95+/-0.20 degrees C for strain 7004, 7.88+/-0.10 degrees C for strain 4342, and 9.13+/-0.16 degrees C for strain 9818.

Behavioural pattern of vegetative cells and spores of Bacillus cereus as affected by time-temperature combinations used in processing of Indian traditional foods

“…A similar situation was also reported for a strain of Bacillus anthracis Sterne (Novak et al 2005). The D-values recorded in the present study for three cultures of B. cereus were almost closer to those values reported earlier for the strain of B. cereus ATCC 4342 and 7004 when subjected to heat treatment in buffers of pH 7.0 and milk medium at 90°C (Montville et al 2005;Moussa-Boudjemma et al 2006) and 95°C (Mazas et al 1999a). In a study with spores of B. cereus ATCC 7004 (Mazas et al 1999b), the D-values recorded at 92 and 96°C in saline and milk medium were quite lower to those observed in this study.…”

“…The thermal inactivation pattern of spores of B. cereus cultures observed in most of the earlier studies have revealed that D-values differ very much depending primarily on the strains used and to a lesser extent the extrinsic and intrinsic factors. Earlier studies have reported varying D-values for ATCC strains of B. cereus 4342, 7004 and 9818 in buffers and substrates similar to culture broth and those containing food constituents (Mazas et al 1995(Mazas et al , 1999aGonzález et al 1999;Montville et al 2005;Moussa-Boudjemma et al 2006). A similar situation was also reported for a strain of Bacillus anthracis Sterne (Novak et al 2005).…”

Thermal inactivation of Bacillus cereus spores in micellar casein concentrates–effect of protein content and pH development

“…In the present study, no increase in the spore heat resistance was observed with increasing protein and dry matter content of the MCC. Similarly, in skim milk and skim milk concentrates at 8.5% and 17.1% dry matter, Mazas et al (1999) did not find differences in the heat resistance of spores of three different B. cereus strains. The addition of casein in a concentration of 2.5% to the heating medium phosphate buffer did not change the heat resistance of Clostridium sporogenes spores (Amaha and Sakaguchi 1954).…”

“…The heat resistance of the employed, probiotic B. cereus strain is comparable to the heat resistance of other human pathogenic strains (e.g., Mazas et al (1999)). In the present study, no increase in the spore heat resistance was observed with increasing protein and dry matter content of the MCC.…”

Survival of thermophilic spore-forming bacteria in a 90+ year old milk powder from Ernest Shackelton's Cape Royds Hut in Antarctica

“…Additional contributing factors include the preheat-treatment of the powder (Findlay et al 1946), the milk powder structure, storage conditions (particularly the lack of oxygen), the type of organisms present (Thompson et al 1978 ;Kieseker & Aitken, 1993;Celestino et al 1997) and type and concentration of milk solids, i.e. skim or whole milk (Mazas et al 1999). …”