EFFECT OF CALCIUM AND HYDROXYPROPYLATION ON CRYSTALLINITY AND DIGESTIBILITY OF RICE STARCHES

The digestibility of native and hydroxypropyl rice starches in the pre sence 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) wh ich in turn enhanced calcium binding. Depending upon the amount of cal cium added (50-250 mu g calcium per g dry starch) and levels of MS (ra nging from 0.02 to 0.12), 25.4-34.1 mu g calcium was bound per g of hy droxypropyl starch. Native starch bound 25.4 mu g calcium per g dry st arch, which was much less than the hydroxy-propylated starches. Crysta llinity decreased with the increase of MS and calcium concentration. D igestibility of ungelatinised hydroxypropyl starches increased with MS (2.5-4.1 mg reducing sugar released per g dry starch) and the trend i s reversed in the gelatinised form. Calcium-induced amylolysis of the starches by porcine pancreatic a-amylase but somehow inhibited amylogl ucosidase attack. (C) 1998 SCI.