Food component influence on water activity of low-moisture powders at elevated temperatures in connection with pathogen control

Abstract

Recent research has shown exponentially increased thermal resistance of pathogenic bacteria at a reduced water activity (aw) in thermal treatments. However, information on aw change as affected by food components at high temperatures is limited. The objective of this project was to quantify the influence of major food components on aw changes in low-moisture foods at elevated temperatures. Corn starch, soy protein, coconut, and cheddar cheese powders were selected as high-carbohydrate, high-protein, high-fat, and intermediate products. Vacuum dried powders were equilibrated in the jars containing saturated salt solutions to different aw from 0.11 to 0.84 at 25 °C. The aw of food powders were measured from 25 to 80 °C in hermetically sealed test cells using hight-temperature humidity sensors. For a given initial aw, high-carbohydrate product had more considerable aw increase than high-protein, intermediate, and high-fat foods with increasing temperature. The net isosteric heat of sorption increased from high-fat, intermediate, high-protein, to high-carbohydrate food at same moisture content. These relationships support findings in the literature that bacterial cells are more easily inactivated in high-carbohydrate and high-protein products than in high-fat foods. Understanding the correlation between food components and aw change at elevated temperatures helps predict the thermal resistance of bacteria in low-moisture foods.