Corn dry-milled grit and flour fractions exhibit differences in amylopectin fine structure and gel texture

Corn starch amylopectin (AP) fine structure and gel textural properties of dry-milled grit and flour fractions were investigated in 10 corn cultivars. Amylopectin was isolated by fractionating the starch derived from these two milled fractions using size-exclusion chromatography (SEC). Fine structure was characterized by SEC after thorough debranching with pullulanase. SEC revealed three major fractions of debranched AP from the grit and flour portion. Amylopectin in the grit portion had a significantly higher proportion of long chains (DPn 70-75) and a postulated lower extent of chain branching than its flour counterpart. Texture profile analysis showed that flour gels from the grit fraction had significantly higher values for hardness, gumminess, and springiness compared with gels from the floury fraction. Trends were similar for starch gels of the two dry-milled fractions, though only springiness was significantly different. The finding that differences in AP fine structure in dry-milled fractions relate to gel textural differences suggests that dry millers may be able to produce flours of different functionalities that would be suited for different end uses. Additionally, mixing the dry-milled flour fraction with a grit-derived flour would result in different product properties.