Effect of grain structure and cooking method on starch digestibility and antioxidant activity of amaranth (Amaranthus caudatus L.) grains during simulated gastrointestinal digestion

•Grain structure influenced starch hydrolysis during simulated digestion.•Cooking method affected on antioxidant activity of amaranth during digestion.•Cooking increased starch hydrolysis of amaranth grains during digestion.•Boiling and roasting caused grains to release more polyphenols during digestion.•Roasting was more beneficial for the functions of amaranth grains than boiling. Amaranth has received widespread interest as a high-quality source of nutrition. This study examined changes in starch hydrolysis and antioxidant activity of intact or slurry of amaranth grains, which were cooked with different methods, such as boiled and roasted, during simulated in vitro gastrointestinal digestion. The starch digestibility of amaranth samples was analyzed using starch hydrolysis percentage and digestion kinetics during simulated digestion. Simultaneously, TPC and antioxidant assays, such as ABTS, FRAP, and MIC, assessed the changes in antioxidant potential during digestion. The results showed that the slurry increased starch hydrolysis and antioxidant properties compared with intact grain. Boiling and roasting also showed increased antioxidant activity and starch hydrolysis during digestion. Whether intact grains or slurries, the roasted samples had lower starch hydrolysis and higher antioxidant properties during digestion than the boiled samples. The equilibrium starch hydrolysis percentages of the roasted and boiled intact grains were 15.50 and 67.41 %, and those TPC were 662.78 and 470.21 mg GAE/100 g sample (db.), respectively. In this study, roasting was more beneficial in delaying starch hydrolysis and improving antioxidant activity than boiling. In addition, maintaining the grain state was more conducive to controlling starch hydrolysis. Our findings could be beneficial for the amaranth consumers.