Effects of storage temperatures and essential oils of oregano and nutmeg on the growth and survival of Escherichia coli O157:H7 in barbecued chicken used in Iran

Abstract

Traditional Iranian barbecued chicken (TIBC) consists of cubed chicken breast, lemon juice, onion, saffron, salt, red pepper, vegetable oil and various spices such as oregano and nutmeg with pH value about 5.5. As this product is sometimes consumed under-cooked, there is growing concern that it may pose health hazards to consumers related to pathogenic bacteria such as Escherichia coli O157:H7. We studied the influence of storage temperature and essential oils (EOs) of oregano and nutmeg on the growth and survival of E. coli O157:H7 in ready-to-cook TIBC. Ready-to-cook TIBC was prepared according to the traditional practice using different concentrations of oregano and nutmeg EOs. The TIBC and control samples (TIBC without the EOs) were spiked with E. coli O157:H7 to a final concentration of 6–7 log 10 CFU g −1 and stored at 3, 8 and 20 °C. E. coli O157:H7 was counted after 0, 24, 48 and 72 h storage using MacConkey sorbitol agar supplemented with cefixime and tellurite. The EOs of oregano and nutmeg had a bactericidal effect on E. coli O157:H7 in broth culture with 0.6 and 10 μl ml −1 concentration, respectively. The log 10 CFU g −1 of E. coli O157:H7 count in the spiked samples, containing 1, 2 and 3 μl g −1 of EOs of oregano and nutmeg that were stored at different temperatures for up to 72 h relative to the control samples did not change. Increasing the storage temperatures from 3 °C to 20 °C up to 72 h significantly increased the log 10 CFU g −1 of E. coli O157:H7 in both experimental and control samples. The results showed that the E. coli O157:H7 had the ability to survive in ready-to-cook TIBC at refrigeration condition (3 °C) and multiplied significantly at the higher temperature, e.g. 8 °C and the ambient temperature of 20 °C. The results from our study showed that contrary to the inhibitory effect of EOs of oregano and nutmeg against E. coli O157:H7 in broth system, they had no any inhibitory effect against E. coli O157:H7 in ready-to-cook TIBC.