In vitro starch digestibility, degree of gelatinization and estimated glycemic index of foxtail millet-derived products: Effect of freezing and frozen storage

• Freezing process and the first day of frozen storage were main factors of starch digestibility.
• Pregelatinized starch may increase the glass transition temperature of final product.
• The variation trends of DG, eGI and in vitro starch digestibility were basically the same.
• Frozen storage products are available for long-term dietary intervention.

To analyze the effects of the freezing process, frozen storage temperature and frozen storage time on starch digestion characteristics, 3 kinds of foxtail millet-derived products were produced and frozen stored at −18 °C or −40 °C. The in vitro starch digestibility, degree of gelatinization (DG) and estimated glycemic index (eGI) of reheated samples were investigated after frozen for 1, 3, 5, 7, 14, 21 and 28 days respectively. The results showed that the variation trends of DG, eGI and rapidly digestible starch content were basically the same during freezing and frozen storage. Starch digestion characteristics of frozen millet products stored at −40 °C were more stable than those of counterparts stored at −18 °C. The first two weeks, especially the first day of frozen storage, had a greater effect on starch digestibility, as compared to the rest days of frozen storage. Thus fresh prepared foxtail millet-derived products are required for determining the glycemic index of specific food or conducting a short-term dietary intervention while frozen stored products are available for long-term intervention. Moreover, addition of pregelatinized starch into millet pancake may increase its glass transition temperature and thus decrease its degradation rate.