Ethanol pretreatment increases the efficiency of maltogenic α-amylase and branching enzyme to modify the structure of granular native maize starch

A method for efficient functional modification of starch granules by thermal ethanol pre-treatment and subsequent maltogenic alpha-amylase (MA) and branching enzyme (BE) post-treatments is described. Ethanol pretreatment significantly increased the swelling power of starch granules thereby increasing the MA and BE susceptibility. Ethanol pre-treated granules became shrunk and twisted after incubating in buffer. Sequential MA post-treatments remarkably increased the alpha-1,6 to alpha-1,4 ratio and the content of amylopectin short chains (DP 1-10), contributing to the low retrogradation rate. BE post-treatments significantly decreased the product yield, increased the relative crystallinity of starch granules, suggesting BE had intramolecular transglucosylation activity which altered the branch position and reduced the molecular size by forming cyclic structures. Moreover, BE post-treatments showed an alpha-1,6 to alpha-1,4 transglucosylation activity by decreasing the alpha-1,6 to alpha-1,4 ratio, especially during simultaneous MA and BE catalysis. However, in the simultaneous MA and BE post-catalysis, MA dosage was predominant by noticeably hydrolyzing amylopectin and amylose molecules and increasing the alpha-1,6 to alpha-1,4 ratio, thereby leading to the lowest digestibility and retrogradation.

Automated summary

This study outlined a method for efficient modification of starch granules by using thermal ethanol pre-treatment followed by maltogenic alpha-amylase (MA) and branching enzyme (BE) post-treatments. The sequential MA post-treatments increased the alpha-1,6 to alpha-1,4 ratio and the content of amylopectin short chains, while BE post-treatments decreased product yield and increased relative crystallinity. Simultaneous MA and BE post-catalysis showed MA dosage was predominant in hydrolyzing amylopectin and amylose molecules, ultimately leading to the lowest digestibility and retrogradation.