Chemical composition and in vitro starch digestibility of corn tortillas with added amaranth flour

BACKGROUND: Corn tortillas containing 20% (w/w) amaranth flour (AF) were kept in cold storage and analysed after various times for chemical composition and in vitro starch digestibility, including predicted glycemic index. Comparison was made with traditional nixtamalised corn flour (NCF) tortillas. RESULTS: Lipid and protein contents were higher in mixed NCF/AF tortilla than in NCF tortilla. Available starch (AS) content was lower in NCF/AF tortilla and decreased during cold storage. However, this decrease was greater in NCF tortilla, suggesting slower starch retrogradation in NCF/AF tortilla. After 96 h of storage, total resistant starch (RS) content was higher in NCF tortilla than in NCF/AF tortilla. However, no differences were detected thereafter, indicating similar retrogradation after long storage times. Retrograded resistant starch contents indicated that only part of the total RS in tortilla is due to retrogradation, which agrees with the tendency recorded for AS and RS in both types of tortilla. α-Amylolysis rates were similar in NCF/AF and NCF tortillas, decreasing with storage. The predicted glycemic index was always higher in NCF/AF tortilla, a pattern that might be due to the waxy-type starch present in AF. CONCLUSION: NCF/AF tortilla might be suitable as a product with higher protein content and higher glycemic index than conventional NCF tortilla.