Effects of germination combined with extrusion on the nutritional composition, functional properties and polyphenol profile and related in vitro hypoglycemic effect of whole grain corn

A combination of germination and extrusion was applied to whole grain corn to increase its nutritional composition, functional properties and non-anthocyanin polyphenol profile, especially related to in vitro hypoglycemic effects. Individual germination and extrusion both led to an increase in soluble dietary fiber and lysine, methionine , tryptophan content, while insoluble dietary fiber content decreased. Extruded germinated whole corn flour (EGWCF) had a higher water absorption and solubility index, showing 103 and 575% increases over untreated ones, respectively. Germination increased free, bound phenolic acid and bound flavonoid content to 169, 230 and 311%, respectively. The total phenolic acid and flavonoid content of EGWCF was 260 and 249% of WCF, respectively. Germination increased the polyphenol composition from 12 to 15 species. Phenolic profiles of EGWCF exhibited collective effects, showing three new phenolic compounds . Polyphenol extracts showed more potent activity against α -glucosidase rather than α -amylase. Free form polyphenols had stronger inhibitory activity than the bound forms. Compared with WCF, free and bound polyphenol extracts from EGWCF increased the anti- α -glucosidase activity by 221 and 40%, and increased the anti- α -amylase activity by 105 and 108%.