LAUSR

Starch retrogradation during freeze drying is a contributor to an undesirable decrease in the viscosity of soup prepared from instant soup with high starch content. Monitoring starch retrogradation during drying is therefore of importance if such a process is to be optimized. Here, cream mushroom soup was used as an example of high-starch instant soup. Drying and quality characteristics of the soup during freeze drying was first studied. Although freeze drying preserved much quality of the soup, it led to significant decrease in the viscosity. Following the data on starch retrogradation, drying characteristics and quality (in terms of whiteness, Shrinkage ratio and rehydration behavior) of the freeze-dried product, three-step hybrid drying strategy viz. microwave drying (0.8 W/g, for 1 h) + freeze drying (50 °C, for 4 h) + microwave drying (0.8 W/g, until the end of drying) was successfully developed to avoid viscosity reduction while maintaining other quality characteristics of the soup.