Growth and toxigenic potential of Bacillus cereus during storage temperature abuse in cooked irradiated chicken rice in combination with nisin and carvacrol

• Cooked chicken rice was treated with gamma irradiation combined to nisin and / or carvacrol.
• Combined treatments resulted in a significant decrease of Bacillus cereus count at 10 °C.
• Delaying of toxin production was observed for all combined treatments.
• Reduced PC-PLC activity was also obtained for all combined treatments.

This study investigated the effect of combined treatments involving low doses of gamma irradiation in combination with nisin and carvacrol as antimicrobial agents on the growth and potential toxicity of Bacillus cereus, during storage temperature abuse. The chicken rice was spiked with endospores and was incubated at 10 °C for 2 weeks. Microbial population was examined using plate counting on MYP agar. Toxigenic potential was measured through the record of enterotoxins and phosphatidylcholine-specific phospholipase C (PC-PLC) activity. The results showed that samples processed with a combination of low irradiation dose; (D10, ½ D10) and reduced concentration of antibacterial agents (MIC, ½ MIC), resulted in a significant decrease (p ≤ 0.05) of B. cereus count compared to the samples treated only with higher amount of antimicrobial agents (2 × MIC). Toxin production was also delayed by irradiation and a total absence of enterotoxin was observed in irradiated rice at 1.8 kGy in the presence of nisin alone or in combination with carvacrol until the 12th day of storage at 10 °C. Reduced proliferation of B. cereus obtained by combined treatment was associated with a limitation of toxin production and led systematically to significant decrease (p ≤ 0.05) of PC-PLC activity during storage.