Influence of extrusion on the physicochemical properties, proximate composition, phenolic profile and antioxidant activity of finger millet seed coat and endosperm rich fractions

Abstract

Finger millet seed coat and endosperm are abundant sources of phytonutrients. This study aimed to investigate the application of extrusion technology to convert finger millet seed coat and endosperm into instant ingredients and to assess their physicochemical, nutritional, phenolic, antioxidant and product-forming qualities. Extrusion significantly enhanced sedimentation values in both the extruded finger millet seed coat (ESC) (355%) and the endosperm-rich fraction (EEF) (353%). Proximate analysis showed no significant changes in the protein content, whereas the total dietary fiber decreased (63%) in ESC and increased (23%) in EEF. Total phenolic content was retained by 57% and 74% in ESC and EEF, respectively, while the flavonoid content remained relatively high in ESC (70%) and EEF (81%). The major phenolics identified were catechin (CAT) and p-catechuic acid (PCAT). In ESC, free cat and p-cat were retained by 56% and 24%, respectively, whereas bound cat retained by 42%, and p-cat exhibited an increase of 118%. Conversely, EEF showed no significant changes in free cat, while free p-cat was retained by 76%, and the bound cat and p-cat were retained by 46% and 50%, respectively. The extruded fractions showed a reduction in antioxidant activity in both ESC and EEF. Pasting properties were decreased on extrusion in EEF. Instant beverages prepared using ESC and EEF exhibited acceptable organoleptic properties. In conclusion, through extrusion technology it is possible to develop functional food ingredients rich in antioxidants and phenolic compounds from finger millet.

Graphical abstract