Abstract
We investigated the ability of biofilm formation, survival, and behavior of diarrheal and emetic Bacillus cereus vegetative cells and spores in tofu. Both diarrheal and emetic B. cereus did not proliferate at a temperature below 9 °C in tofu. However, the emetic B. cereus grew faster than diarrheal B. cereus at 11 °C and had better survival ability at low temperatures. Both diarrheal and emetic B. cereus were able to form a biofilm on stainless steel. These biofilm cells were transferred to tofu in live state. The transferred biofilm cells could not grow at a temperature below 9 °C but grew over 11 °C, like planktonic cells. B. cereus contamination in tofu at a high concentration (>6 logs CFU/g) was not entirely killed by heating at 80, 85, or 90 °C for 2 h. Spores and emetic B. cereus had higher resistance to heat than vegetative cells and diarrheal B. cereus, respectively.
Highlights
Tofu, a soy-based food, is known to be healthy because it has low calories and large amounts of proteins (41.3%) with all nine essential amino acids
These results indicated that the survival ability of emetic B. cereus strain was better than that of diarrheal B. cereus strain in tofu at both temperatures
The efficiency of transfer (EOT) value of emetic B. cereus (0.81 ± 0.12) was higher than that of diarrheal B. cereus (0.72 ± 0.05), there was no significant difference in EOT value between these two types of strains (p > 0.05)
Summary
A soy-based food, is known to be healthy because it has low calories and large amounts of proteins (41.3%) with all nine essential amino acids. It is an excellent source of iron, calcium, and other micro-nutrients [1]. Because of these health benefits, consumption of tofu has increased. The safety of tofu in the retail market should be guaranteed. Due to its high protein, high water content, and neutral pH, tofu provides perfect conditions for the growth of microorganisms [2]. Lee et al [4] have found two species of B. cereus in tofu stored at 37 ◦C for 24 h
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