α-Amylase mediated production of modified potato starch with distinct gel properties

This study examines how seven microbial α-amylases selected from different glycoside hydrolase 13 (GH13) subfamilies (GH13_1, GH13_5, GH13_37, and GH13_42) affect the molecular and physical properties of potato starch with respect to gelation and gel properties. The results revealed distinct degradation profiles, reflecting different preferences for amylose and amylopectin. Rheological analysis of the starch gels revealed that, notably, starch treated with Um-αAmy, a GH13_37 α-amylase from an uncultured marine bacterium, had superior gel properties, while starch treated with catalytically efficient Bacillus-derived α-amylases of GH13_5 exhibited particularly poor gelling abilities. The results suggest that the strong gel properties of Um-αAmy treated starch are likely associated with a preferential, yet controlled, amylose degradation combined with a limited activity on amylopectin. Assessment of the enzyme structure models indicated a possible correlation between active site conformation and starch degradation profiles, with open conformations potentially enabling enhanced amylopectin degrading ability, and thus, poor gelling ability of the resulting starch. Furthermore, the limited thermal stability of Um-αAmy turned out to be a desirable trait, facilitating a more controlled enzymatic starch modification process. Altogether, these findings provide a novel insights into the significance of α-amylase phylogeny and classification in controlled enzymatic starch modification and highlight the potential of selected α-amylases for enzymatic production of modified potato starch with distinct gel properties.