Insect chitosan as a natural antimicrobial against vegetative cells of Bacillus cereus in a cooked rice matrix

Abstract

This study investigates the antimicrobial activity of insect chitosan against vegetative cells of Bacillus cereus in a rice matrix. Sample culture solutions were prepared with different concentrations of insect chitosan (150, 180, 220 and 250 μg/mL) and tested at three temperatures (30 °C, 20 °C and 10 °C), which simulate different storage temperature scenarios of precooked rice. The results indicate that insect chitosan has antimicrobial activity that depends on temperature and chitosan concentration. For the assays with chitosan at 10 °C, all concentrations were bactericidal during the study time, reaching a maximum inactivation of 6 log cycles for 250 μg/mL. At 20 °C and at 30 °C a bacteriostatic activity was observed for concentrations of 150 μg/mL and 180 μg/mL. Results also showed that concentrations of 220 μg/mL and 250 μg/mL were bactericidal for all the temperatures tested during the storage time. When rice is cooked and not stored at an appropriate temperature, below 10 °C, the consumer's health is at risk. In these cases, insect chitosan could be a good additional control measure to control B. cereus growth and toxin formation in cooked rice.

Keywords: Bacillus cereus; Cooked rice; Growth; Insect chitosan.