CONTROL OF SALMONELLA IN SPICES: THERMAL RESISTANCE, STABILITY DURING STORAGE AND SURROGATE

Yucen Xie

doi:10.7273/000004408

Salmonella is one of the common pathogens highly implicated in low-moisture foods. Recent studies indicate that the thermal resistance of Salmonella is determined by the water activity (aw) of low-moisture foods measured at treatment temperature. A quantitative master curve between the thermal-death-time (D80℃-values) for S. Enteritidis and aw at 80 ℃ in low-moisture foods without antimicrobial activities can be obtained by SiO2. Firstly, this dissertation investigated that the bacterial cellular moisture content, adjusted by the aw of low-moisture foods at treatment temperature, is the dominant factor influencing the thermal resistance of bacterial cells in low-moisture foods. Secondly, this study systematically proved that spices with antimicrobial activities could facilitate the thermal inactivation by comparing the log-linear correlations between D-values and aw, treatment-temperature between ground cinnamon and the master curve for other non-spicy low-moisture foods. Thirdly, the antimicrobial activities of the three spice products (chili, cinnamon and black pepper) against Salmonella and Enterococcus faecium were different in room-temperature storage and isothermal treatments. The results showed that the antimicrobial activity of chili was the most effective among the three spices during storage and thermal inactivation. Lastly, this work selected ground cinnamon as an example and evaluated the suitability of E. faecium as a surrogate for Salmonella during thermal inactivation under multiple temperatures and aw. The thermal resistance of E. faecium as a function of aw, treatment-temperature was similar to Salmonella, indicating E. faecium was a conservative surrogate for Salmonella in cinnamon in isothermal treatments. In summary, the cellular moisture content of bacteria in low-moisture foods as influenced by aw of foods during heating is an intrinsic parameter determining the microbial resistance. It highlights the importance of aw at treatment temperature in predicting D-values. A synergistic effect between antimicrobial activities in spices and thermal lethality can be observed, but it varies from spices. Appropriate storage for some spice products may be an alternative to mitigate contamination. In ground cinnamon, E. faecium was still a surrogate for Salmonella. The aw, treatment-temperature of low-moisture foods was no longer the main factor influencing the thermal resistance of bacteria; the antimicrobial activities should also be considered.

CONTROL OF SALMONELLA IN SPICES: THERMAL RESISTANCE, STABILITY DURING STORAGE AND SURROGATE

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