Water Activity at Isothermal Temperature and Its Effect on Microbial Heat Resistance in Low-moisture Foods
2022
Yalan ZHANG | Siqi LV | Shiqi ZHANG | Wen QIN | Shuxiang LIU
Water activity (aw) is the key factor defining low-moisture foods (LMFs, aw,25 ℃<0.85), and also determines the heat resistance of microorganisms in LMFs. However, aw of food is a temperature-dependent factor, and is highly influenced by food components and texture. When temperature rises, aw has shown different trends of changes. Water activity at isothermal temperature (aw,T) reflects the real-time aw of foods during high-temperature pasteurization. Accurate measurement and calculation of aw,T enable scholars to quantify the heat resistance parameters of microorganisms in LMFs, and to design, verify, and improve associated thermal pasteurization processes. However, commercial aw meters can only conduct the measurement at low temperature range (20~50 ℃). Little is known on the aw in the high temperature range (>55 ℃). The microbial safety of LMFs and its microbial heat resistance parameters are first introduced in this article. Then the definition, detection methods, model predictions, influencing factors of aw,T and the effects of aw,T on microbial heat resistance of LMFs are summarized. Recognition and measurement of aw,T are beneficial for food industries to reduce the degree of LMFs microbial contamination and ensure consumers food safety.
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