Effect Of Different Process Methods On The Antioxidant Capacity In Vitro Of Whole Grain Extracts

Brown rice, whole wheat and maize were chosen to be investigated in this study. We studiedthe effect of steaming, boiling and extrusion on the antioxidant capacity in virto of these wholegrains. In order to have a preliminary insight of the mechanism over the alteration of antioxidantcapacity, investigations were involved including the assay on physicochemical indexes of wholegrains after processing, correlation analysis and the interaction between phenols and starch.Firstly, basic components of whole grain were determined. The results showed that nosignificant change occurred to the content of starch, protein and ash after processing. Significantchanges occurred to dietary fiber after extrusion, but no significant change was observed aftersteaming and boiling. Both the contents of fat and reducing sugar showed a significant decreaseafter processing.Secondly, the optimal extraction on free and bound antioxidant substance of whole grain wasestablished by single factor and orthogonal experiments based on phenolic content and DPPHradical scavenging rate. The optimal extraction condition of free antioxidant substance wasobtained as follows: material/solvent1:25,60%ethanol extract for2hours under the temperatureof50°C. The optimal extraction condition of bound antioxidant substance was obtained as follows:2%NaOH hydrolyze for4hours under the temperature of40°C and adjust the pH of thehydrolysate to5before three-extractions of ethyl acetate.Thirdly, physicochemical properties of the three whole grains significantly changed afterprocessing. The effect of extrusion in decreasing the free and bound phenolic content is greater thanthat of steaming and boiling. Steaming is better than boiling at minimizing the loss of free phenoliccontent of and even increasing bound phenolic content; Except for wheat, extrusion can causegreater loss of antioxidant capacity than steaming and boiling, and steaming is better than boiling atretaining and improving antioxidant capacity of whole grains; Process can cause decrease on L*and enhancement on a*, b*and E, which, to some extent, could reflect the intensity of the process;Extrusion can cause great loss of free phenolic acids, however, no free phenolic acids weredetermined after steaming and boiling. On the other hand, extrusion can cause greater loss onbound phenolic acids than steaming and boiling. Generally, steaming can retain and improve theantioxidant capacity of whole grains.Fourthly，correlation analysis showed that significant positive relationships were observedbetween free phenols, bound phenols and bound phenolic acids against trolox equivalentantioxidant capacity (TEAC), DPPH scavenging rate and ferric reducing antioxidant powerpotential (FRAP) indicating that free and bound phenols are the major antioxidants, and phenolic acids are the major components of bound phenols. A significant negative relationship betweenantioxidant capacity and E was observed which means the darker the color the lower antioxidantcapacity of the whole grains. No significant relationship between free phenolic acid and antioxidantwas observed. Moreover, the dietary fiber of raw whole grains have a significant relationship withbound phenols indicating that high dietary fiber in whole grain can exert its antioxidant function inhuman’s intestinal tract and prevent from getting chronic disease.At last, the interaction between starch and phenols was investigated. The results showed thatstarch can absorb water during gelatinization as well as phenols which, to some extent, minimizedthe loss of free phenols and even protected the free phenols from being decomposed.