Effects of heating temperature on the total phenolic compound, antioxidative ability and the stability of dioscorin of various yam cultivars

The purposes of this study were to investigate the effects of different heating temperatures on the antioxidative activity of yams and on the stability of dioscorin of various yam cultivars (Mingchien, Tainung No. 2 and Keelung). Results from crude yam extracts of all varieties showed decreases in total phenolic and dioscorin contents, DPPH radical-scavenging effect, and ferrous ion chelating capacity with increasing heating temperatures. Following separation and purification, only one protein band with the same molecular weight of 31 kDa (dioscorin) was consistently electrophoresized from three peaks of 25–45 fraction numbers from all yam varieties. Fraction numbers of peaks were reduced and peak area narrowed with increasing heating temperatures and no protein could be extracted at temperatures above 80 °C. The dioscorin protein surface hydrophobicity declined with increasing heating temperatures. Significant correlation of dioscorin content with DPPH-scavenging effect was noted for all yam species.