Construction and expression of a transglucosidase-hexose fusion enzyme for oxidating starch: The intrinsic correlation between molecular structure and oxidation degree.

Genetic engineering was utilized to fuse transglucosidase (TG) and hexose oxidase (HOX), producing a fusion enzyme TGHOX. This novel enzyme eenabled a sequence reaction involving starch chain transformation and oxidation in a single system. Compared with native wheat starch (24.07% amylose), TGHOX treatment increased the amylose content of wheat starch, with the TGHOX-16 treatment reaching a maximum amylose content of 41.77%. The A-chain content of wheat starch increased from 31.31% to 41.68% after TGHOX treatment. Higher A-chain content provided more highly accessible non-reducing end substrates for transglycosylation for TGHOX, thereby increasing the branching density of starch to 6.3%. Furthermore, the branched terminals with reactive hydroxyl groups served as abundant substrates for oxidation by the HOX moiety. This, yielded carbonyl and carboxyl content of 0.3847 g/100 g and 0.4003 g/100 g, respectively. The oxidative modification reduced the relative crystallinity of starch from 36.95% to 28.42% and disrupted the intermolecular chain aggregation (from -6.13 mV to -24.91 mV). This green and efficient fusion enzyme system shows promising potential for industrial production of oxidized starch.