Enzymatically modified waxy corn starch with amylosucrase: The effect of branch chain elongation on structural and physicochemical properties

Abstract

Recombinant Amylosucrase (AS) from Neisseria polysaccharea was used to modify waxy corn starch, and the reaction process was monitored by the turbidity and transglycosylation degree (TD). Results showed that the modification by AS significantly elongated the chain length of the starches, resulting in the formation of precipitate. Based on regression equation, AS-modified starches with defined TD values were prepared, and chain length distributions of AS-modified starches indicated that the non-reducing ends of the branch chains were mostly elongated before the occurrence of precipitation. Differ from the native starch, all of the AS-modified starches showed a B-type crystal structure, and thermal analysis suggested that the AS-modified starches containing longer chains possessed a higher thermostability. High resistant starch content (33.8%–73.6%) of AS-modified starches was attributed to the formation of long-ranged double helices. Moreover, the very long chains, produced after the precipitation, might not generate the double helical structure during the retrogradation.