The factors that determine the digestion rate of starches were revealed using different forms of starches and a mixture of α-amylase and amyloglucosidase. Gelatinized starch samples with a degree of gelatinization (DG) from 12.2 to 100% for potato starch and from 7.1 to 100% for lotus seed starch were obtained. With an increasing DG, the short- and long-range molecular orders of both starches were disrupted progressively. The first-order digestion rate constant (k) of both starches increased with an increasing DG, although the positive linear relationships between DG and k differed (R2 = 0.87 for potato starch, and R2 = 0.74 for lotus seed starch). The mean fluorescence intensity showed a positive linear correlation with DG, which was strong for potato starch (R2 = 0.99) and relatively weaker for lotus seed starch (R2 = 0.54). These results indicated that DG is a major determinant for the digestion rate of potato starch and lotus seed starch and that the access/binding of enzymes to starch was the main rate-limiting factor for digestion of starches.
Keywords: degree of gelatinization; digestion rate; enzyme binding; fluorescence intensity; lotus seed starch; potato starch.