FINE-STRUCTURE OF MAIZE STARCHES FROM 4 WX-CONTAINING GENOTYPES OF THE W64A INBRED LINE IN RELATION TO GELATINIZATION AND RETROGRADATION

Maize starches from four wx-containing genotypes (wx, du wx, ae wx, and ae du wx) of the W64A inbred line were examined to determine their gelatinization and retrogradation properties and the fine structure of their amylopectins (AP). Chain-length distribution profiles of the APs showed distinct patterns according to genotype, The wx and du wx starches had a large proportion of short chains and showed A-type X-ray patterns, whereas the ae wx and ae du wx starches had a large proportion of long chains and showed B-type X-ray patterns. The ae wx starch had the highest values of onset melting temperature (T-0) and heat uptake (Delta H), both for gelatinization and after retrogradation, which were attributed to a greater proportion of long chains (degree of polymerization > 16) in the AP. Debranching of beta-limit dextrins also revealed that the interior chain-length distribution of AP from the ae wx genotype constituted a large proportion of long chains. The extent of retrogradation increased in the order wx, du wx, ae wx and ae dy wx starches and appeared to be proportional to the level of unit chains with DP 16-30 and inversely proportional to the level of short chains with DP 6-11.