The substitution pattern in cationised and oxidised potato starch granules

The distribution pattern of substituents within the granules and the compon ents of two cationised and two oxidised potato starches was studied. The le vel of crystallinity in wet-cationised (WC) and hypochlorite oxidised (HO) starch granules was similar to that of native starch granules but lower in dry-cationised (DC) and peroxide oxidised (PO) granules. However, the melti ng temperature of DC granules remained similar to native granules but was d ecreased in the other samples. With all modified starches, the initial rate of acid hydrolysis (lintnerisation) was increased compared to native granu les. The degree of substitution decreased only slightly in WC granules afte r the lintnerisation, whereas virtually all the substituted glucosyl units in DC starch were hydrolysed already at initial stages. The decrease of sub stituents in the HO and PO starches was intermediate. The starches were par tly resistant to the action of isoamylase and the successive beta -amylolys is, suggesting that substituents were found both close to the branches and near the nonreducing ends in the amylopectin component. It is suggested tha t the DC starch was preferentially cationised at the surface of the granule s, whereas WC and oxidised starches were modified throughout the granules. (C) 2000 Elsevier Science Ltd. All rights reserved.