Response surface modeling for the inactivation of Bacillus cereus on cooked spinach by natural antimicrobials at various temperatures

Abstract

This study was conducted to investigate the growth of Bacillus cereus on cooked spinach with natural antimicrobial substances (0.00-0.02% thymol, 0.60-1.30% acetic acid, and 0.00-0.05% nisin) at various temperatures (15, 25, and 35 degrees C) in order to find the best combination of inhibition. Response surface modeling with the Gompertz model equation was used to describe the growth of B. cereus vegetative cells on cooked spinach with natural antimicrobial substances as a function of temperature. The specific growth rate of B. cereus at the highest concentration of thymol (0.02%) was lower than with the other treatments. In particular, the lag time of B. cereus was the longest for combinations thymol 0.02%, acetic acid 0.68%, and nisin 0.03% at 25 degrees C. The predicted values were shown to be significantly in good agreement with experimental values because the adjusted determination coefficient (R-adj(2)) was 0.91 and the level of significance was p<.0001. Besides, bias factor (B-f) values of the SGR and LT for B. cereus were 1.07 and 1.10, respectively, indicating that they were mostly at the acceptable level. In sensory evaluation, appearance and color of cooked spinach with antimicrobial substances was similar to the control. Practical applicationsNatural antimicrobials could be used as the preservation method to improve the food safety of cooked foods such as cooked vegetables.