Effect of purple yam flour substitution for wheat flour on in vitro starch digestibility of wheat bread

This study aimed to investigate the effect of purple yam (Dioscorea alata L.) flour substitution for wheat flour on in vitro starch digestibility of wheat bread. The enzyme-resistant starch content increased from 34.9% for wheat flour bread to 41.3% for bread made with 70% wheat flour and 30% purple yam flour. Meanwhile, the content of rapidly digestible starch and slowly digestible starch decreased with the addition of purple yam flour in the bread. The results from differential scanning calorimetry, X-ray diffraction, polarized light and scanning electron microscopy showed that purple yam starch granules were not completely disrupted during bread baking. The fluorescence intensity of α-amylase and amyloglucosidase was reduced in bread made with purple yam flour. The decreased digestibility of starch in bread made with purple yam flour was due to the relatively intact starch granules from purple yam flour and possibly an inhibitory effect on digestive enzymes by purple yam flour.