Estudo do comportamento de Bacillus cereus em leite em pó reconstituído submetidos a diferentes tratamentos térmicos e condições de armazenamento.

Abstract

Bacillus cereus is a major concern in the dairy industry. Its spores are resistant to heat and chemicals. This microorganism is frequently associated with intoxications due to the production of toxins such as cerulide, cytotoxin K, hemolysin BL and non-hemolytic enterotoxin. This study aimed to evaluate the spore survival of 12 strains of B. cereus reconstituted in whole milk powder in settings where milk powder is usually prepared in homes, hospitals and food and nutrition services such as direct flame heating, microwave heating, room temperature maintenance and storage in a domestic refrigerator. Powdered milk artificially contaminated with B. cereus spores (n=36) was reconstituted with sterile distilled water before each treatment. Spore counts of B. cereus were made before and after the simulation of each scenario. The counts were made on nutrient agar and TSB supplemented with polymyxin and optical microscopy by Gram stain. The number of decimal reductions (γ) after each treatment was complete for each strain, considering the population before and after specialized treatment. The (γ) firing by direct flame heating ranged from 0,18 UFC to 0,93 UFC (strains B94 and B63) for plant cells for spores a and ranged from 0,76 UFC to 0,08 UFC (B18 and B3). For microwave heating the γ of vegetative cells varied from 0,15 UFC to 1,23 UFC (strains B3 and B51) and for spores the variation was from 0,14 UFC to 0,77 UFC (B3 and B18). For maintenance at room temperature for 2 hours, γ ranged from -0,19 UFC to 0,18 UFC (CCGB512 and B94) and for spores it ranged from 0 (CCGB432 and CCGB512) to 0,72 UFC (B51). For the scenario of storage for 24 hours in a refrigerator at 10°C the γ for plant cells ranged from -0,24 UFC to 0,31 UFC (CCGB511 and B51) and for the spores 0,39 UFC to -0,32 UFC (B51 and B86). The results indicated that two groups of strains could be observed, a resistant group for which the γ was less than 1 and a sensitive group, for which greater reductions were observed 1 γ UFC. The results highlight that the storage conditions of the reconstituted milk after the treatment by direct flame, dissipation and room temperature were not able to provide more than 1 γ UFC. reduction of B. cereus, potentially susceptible to public health if contaminated powdered milk is consumed. The microwave obtained a reduction greater than 1 γ UFC the treatment that promoted the greatest reduction in both vegetative cells and spores of the best strains.