Effects of drying methods on starch crystallinity of gelatinized foxtail millet (α-millet) and its eating quality

The present study analyzed the effects of drying methods, namely freeze drying (FD), hot air drying (HAD) and microwave drying (MD), on the eating quality of gelatinized millet (α-millet) products and the reasons for quality deterioration. Results showed that HAD and MD both led to remarkable deterioration as indicated by slow rehydration and hardened mouthfeel compared to FD. Based on analyses of the microstructures and hydration properties of α-millet as well as the crystallinity of starch therein, the deterioration was ascribed not only to the great shrinkage of dried products but also to starch crystallization caused by HAD and MD. The crystallization was more readily to occur when the material was dried by high-temperature approaches to a moderate or low moisture content (<46%), resulting in the development of V-type crystalline structure, which greatly restricted the hydration properties of pregelatinized millet starch as well as fast rehydration of dried products.