Characterization of Corn Starch Granules Modified by Glucan 1,4-α-Maltotriohydrolase from Microbacterium imperiale

In this study, glucan 1,4-a-maltotriohydrolase (AMTS) is used to modify corn starch granules to elucidate the structural and physical property changes following AMTS modification. The degree of hydrolysis (DH) of granular corn starch is modulated by adding various amounts of AMTS. Pore structures with more pores, deep channels, and cavities in starch granules with extended hydrolysis are observed by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The short-range ordered structure, lamellar structure, and crystalline structure are significantly enhanced under moderate AMTS modification, and then slightly decreased with further modification. These structural changes significantly improve oil and water absorption capacities, decrease solubility and swelling power, diminish pasting properties, and lower the digestibility of granular corn starch. When AMTS interferes with the starch system, the specific surface area of granular starch gradually increases with extended hydrolysis, with the maximum being almost 4.6-fold that of native starch. All these results suggest AMTS hydrolysises of corn starch granules through an "inside-out" pattern, preferential hydrolysis of the amorphous region, and subsequent alternate hydrolysis of the amorphous and crystalline regions. Overall, AMTS is a potential granular starch hydrolase for producing porous starch used as the carrier material in a variety of food applications.