Effect of Extrusion Processing on Antioxidant Activities of Corn Extrudates Fortified with Various Chinese Yams (<Emphasis Type="Italic">Dioscorea</Emphasis> sp.)

The purpose of this experiment was to evaluate the effects of extrusion on antioxidant abilities of the extrudates of corn fortified with various (Chinese) yams. The flours from three yam varieties were used, including Dioscorea alata L. var. Tai-nung No.1 (TN1), D. alata L. var. Ta-shan (TS), and Dioscorea doryophora var. Hang-chun (HC). One commercial yam flour (TJ) was also used. Six antioxidant assays were conducted, such as 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging effect, oxygen radical absorbance capacity (ORAC) assay, ferrous ion chelating (FIC) ability, 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) free radical scavenging activity, superoxide radical scavenging (SORS) assay, and thiobarbituric acid reactive substances (TBARS) assay. The influences of extrusion on the antioxidant activities of corn were determinedly different in different assays, showing a dramatic increase of ABTS value but significant reductions of SORS and TBARS values. The effects of extrusion on antioxidant activities of corn–yam mixtures varied with yams in different assays. Overall, extrusion processing increased the TBARS inhibition ability for all yams and generally had no negative impact on DPPH, ORAC, FIC, and ABTS antioxidant abilities for most yams in corn–yam extrudates. The involvement of the addition of yam to the antioxidant activities of corn–yam extrudates during extrusion could be suggested through two different possible approaches, the effects of extrusion on the antioxidant activities of yams (susceptible, resistant, or improved), and the effects of added yams on the antioxidant activities of corn during extrusion.