Inactivation kinetics of Bacillus cereus and Geobacillus stearothermophilus spores through roasting of cocoa beans and nibs

摘要

Bacillus cereus and Geobacillus stearothermophilus are spore-forming bacteria of concern for the quality and safety of cocoa-based foods, because of their frequent occurrence in raw materials and the capability of spores to withstand heat processing. Cocktails of spores of B. cereus and G. stearothermophilus strains were separately inoculated on cocoa beans and nibs and roasted using a laboratory equipment at 110 degrees C, 125 degrees C and 140 degrees C for up to 600 min to simulate an industrial roasting process. The period of time needed for the first log-reduction S for the spores of the cocktail of B. cereus in cocoa nibs at 110 degrees C, 125 degrees C and 140 degrees C were 92.2 min, 30.5 min, and 17.2 min, respectively. In cocoa beans at 110 degrees C, 125 degrees C and 140 degrees C delta-values were 148.5 min, 55.9 min, and 23.3 min. The 8-values for the spores of the cocktail of G. stearothermophilus in cocoa nibs at 110 degrees C, 125 degrees C, and 140 degrees C were 105.0 min, 39.6 min and 30.4 min, respectively, and 183.6 min, 76.2 min and 49.1 min in cocoa beans at the same temperatures, respectively. The a, of cocoa nibs and cocoa beans ranged between 0.687 and 0.753 before roasting, and between 0.355 and 0.528 after roasting, respectively. The roasting process on beans or nibs applied in the cocoa industry may have a limited effect on the inactivation of naturally present spore forming bacteria.