Effect of calcium and hydroxypropylation on crystallinity and digestibility of rice starches

Abstract

The digestibility of native and hydroxypropyl rice starches in the presence of calcium was investigated. Calcium interacted with native and hydroxypropyl rice starches and altered their relative crystallinity. Hydroxypropylation was measured in terms of molar substitution (MS) which in turn enhanced calcium binding. Depending upon the amount of calcium added (50–250 μg calcium per g dry starch) and levels of MS (ranging from 0·02 to 0·12), 25·4– 34·1 μg calcium was bound per g of hydroxypropyl starch. Native starch bound 25·4 μg calcium per g dry starch, which was much less than the hydroxy-propylated starches. Crystallinity decreased with the increase of MS and calcium concentration. Digestibility of ungelatinised hydroxypropyl starches increased with MS (2·5–4·1 mg reducing sugar released per g dry starch) and the trend is reversed in the gelatinised form. Calcium-induced amylolysis of the starches by porcine pancreatic α-amylase but somehow inhibited amyloglucosidase attack. © 1998 SCI.