Different variations in structures of A- and B-type starches subjected to microwave treatment and their relationships with digestibility

In this study, normal maize starch (NMS, A-type) and potato starch (PS, B-type) were treated with microwave at different power (2.06 W/g and 6.63 W/g), and the variations in structure and digestibility were studied. XRD, 13C NMR and 1H NMR revealed that microwave treatment caused the decrease in relative crystallinity, double helices content and degree of branching. Moreover, the destructive effects on PS were greater than NMS. These structural variations caused the increase in slowly digestible starch and decrease in resistant starch. Besides, the NMS with pores on surface belongs to “inside-out” digestion pattern, and its crystalline structure and helical structure were the crucial factors influencing the digestion. For PS with smooth surface, its digestion pattern is “exo-pitting”, and the morphological structure may be the first barrier to enzymatic hydrolysis. After high-power microwave treatment (6.63 w/g), the digestion pattern of PS was changed due to the appearance of hollows in starch surface.