Studies On The Occurrence And Inhibition Of Bacillus Cereus In The Manufacture Of Fermented Soybean Curd

The soy bean foods are traditionally consumed by the majority of Chinese, however, The opportunistic pathogen of Bacillus cereus has been reported in some kinds of these products in recent years, which may result in the damage of the consumers health and the product export seriously. In this research, the pathogen’s occurrence in5soy bean foods, its appearance during different stages of sufu (fermented soy bean curd) manufacture, and the inhibitory effect by3plant essential oils were investigated respectively, the results were displayed as followed.Firstly, the occurrence Bacillus cereus in5soy bean foods was investigated. Total44samples of5soy bean foods including sufu, fermented black bean, soy bean paste, tofu and soy milk were purchased from local supermarket, retail outlet or farm market, then the total bacterial count and Bacillus cereus count of the samples were analyzed, the results showed that84.2%sufu was contaminated by Bacillus cereus with considerable level of103CFU/g～105CFU/g,21%of them was not able to meet the export standard set by Food and Environmental Hygiene Department of Hongkong, which may cause health hazard to consumers.Secondly, the appearance of Bacillus cereus during different stages of sufu manufacture was evaluated. Over10samples in different making stage including raw soy milk, boiled soy milk, tofu, tofu whey, sour tofu whey, starter culture, salty water, pehtze, salted pehtze and so on were taken from one sufu manufacture, then the total bacterial count and Bacillus cereus count of the samples were determined. The results indicated that the contamination of this pathogen may be caused by the bad environmental condition of production field or unsuitable disinfection method, and the re-use of some raw material, since high level of Bacillus cereus was found in sour tofu whey, starter culture and salty water, which arrived103CFU/g,104CFU/g and105CFU/g respectively. Some suggestions have been given to reduce this pathogen in the manufacture of this product.The thirdly, the inhibitory effect of plant essential oil on Bacillus cereus was also researched. Three plant essential oils including garlic, cinnamon and pepper essential oil were introduced into sufu soup so as to decrease the level of Bacillus cereus, which was intentionally added, the results indicated that all the3essential oil were able to decrease the level of this pathogen from106CFU/ml to104CFU/ml with the concentration of10"9garlic essential oil,10-7cinnamon essential oil and10"6pepper essential oil respectively. Under the base of above research, the TEM was employed to observe the cell figuration of Bacillus cereus, which was treated by garlic essential oil beforehand, the results displayed that the wall of some cells and spores was destroyed, implying good application prospect.