Maltogenic amylase has a non-typical impact on the molecular and rheological properties of starch

The effects of different amylases on the rapid visco analysis rheological properties of starch were studied and the accompanying changes in the starch molecular properties were analyzed with high performance size exclusion chromatography. Different amylases affect the rheological properties of starch slurries and the molecular weight of the starch molecules to a degree depending on their mode of action and properties such as thermostability. Endo-amylases generally reduced the viscosity and the amylose and amylopectin molecular weight (MW) whereas an exo-amylase had little effect. In contrast, a maltogenic amylase from Bacillus stearothermophilus had a markedly different effect on the rheological and molecular properties of starch. Remarkably, the cold paste viscosity (CPV) exceeded that of the control slurry even at high enzyme dosages. Furthermore, this enzyme specifically affected the amylose population, which gained in monodispersity while largely maintaining its MW. In addition, an interesting relationship between CPV and amylose peak degree of polymerisation was found. These results may contribute to a better understanding of amylase functionality in bread making.