Ascorbate radicals in fresh cow's milk.
Using ESR, a weak signal identified as the ascorbate free radical was observed in fresh cow's milk. The signal was unchanged after storage at 5 degrees C for 24 h but disappeared after storage at 25 degrees C. A marked increase in the steady-state ascorbate radical concentration was observed with the addition of H2O2 or xanthine; the increase was abolished in the presence of azide. Based on the xanthine-oxygen reductase activity and 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulfonic acid) peroxidase activity, cow's milk contains 0.45 microM xanthine oxidase and 0.32 microM lactoperoxidase. The results suggest that H2O2- and xanthine-induced ascorbate radical formation was due to the ascorbate peroxidase activity of lactoperoxidase in cow's milk.
Research Institute for Electronic Science, Hokkaido University, Sapporo.
M
M
Nakamura
D000818:Animals; D001205:Ascorbic Acid / Q000737:chemistry*; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000737:chemistry*; D008892:Milk / Q000737:chemistry* / Q000201:enzymology
D005609:Free Radicals; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid