Slowly digestible starch from debranched waxy sorghum starch: preparation and properties

Effects of debranching time, storage time, and storage temperature on production and structural properties of slowly digestible starch (SDS) were investigated. Waxy sorghum starch was hydrolyzed by isoamylase for various times (0-24 hr), and the variously debranched products were stored at -30, 1, and 30 degrees C for 1-6 days. Optimal conditions for SDS production were isoamylase treatment for 8 hr and storage at 1 degrees C for three days, resulting in SDS content of 27.0% in the optimum product. Microscopic observation revealed that rapidly digestible starch (RDS) and SDS were removed from the edges and surfaces of the optimum product by alpha-amylase digestion. Digestion conditions that removed RDS and SDS resulted in a residue with a higher transition temperature and enthalpy than raw starch on a differential scanning calorimetric thermogram. Removal of RDS alone did not cause distinct decrements of peak temperature (T(p)) and enthalpy (deltaH) compared with stored starch. The optimum SDS product showed an amorphous type of X-ray diffractogram. Digestive removal of RDS from the optimum product gave a residue with X-ray peaks similar to B type, which supports that it is partly crystalline. Removal of RDS and SDS gave broader peaks in the X-ray pattern.