Effects of water on the physical properties of food

Abstract

Solid food products are typically in an amorphous state, and their physical properties change dramatically at the glass to rubber transition temperature (Tg). Tg decreases with increasing water content because of water plasticizing effects. When Tg becomes lower than the ambient temperature, a glass to rubber transition occurs at the ambient temperature. The water content at Tg=25℃ is usually described as the critical water content (wc). In this review, the effect of glass to rubber transition on the texture of cookies, the caking of mango powder and the compressibility of soup powder is explained. Tg of the food samples was evaluated by differential scanning calorimetry or thermal rheological analysis. wc was determined from the relationship between Tg and water content. Fracture properties of the cookie samples changed from brittle to ductile at wc. Caking of mango powder occurred at water contents above wc. Hardness of soup powder compressed at temperatures above Tg was much higher than when compressed at temperatures below Tg.