Effect of Extrusion on the Hydrophilic Antioxidant Capacity of Four Whole Grains

Cereal grains are generally subjected to thermal treatment before consumption. However, few data are available on total phenolic content (TPC), degree of starch gelatinization, phenolic acids, and antioxidant capacity of extruded whole grains based on trolox equivalent antioxidant capacity (TEAC), DPPH radical scavenging activity, and ferric reducing antioxidant potential (FRAP). Four whole grains, brown rice, wheat, maize, and barley were examined in this study. The free and bound TPCchanged significantly (p < 0.05) after extrusion. Morever, heat and degree of starch gelatinization could affect the bound TPC. In bound fraction, the antioxidant capacity was directly influenced by TPC. Extrusion (110-140°C) can retain or improve the antioxidant capacity in its free and bound fractions. Phenolic acids are stable in their bound form. Results showed that the bound TPC and total phenolic acids have a strong relationship against antioxidant capacity, indicating that TPC is the major antioxidant in the bound fraction.