THE VARIATION OF SUPEROXIDE-DISMUTASE (SOD) AND XANTHINE-OXIDASE (XO) ACTIVITIES IN MILK USING AN IMPROVED METHOD TO QUANTITATE SOD ACTIVITY

An improved method for determination of superoxide dismutase (SOD) in milk has been developed. The interference of endogenously occurring xanthine oxidase (XO) has been substantially reduced by addition of an ultrafiltration step, which removed 61 +/- 10 (mean +/- SD) % of the XO activity. This method was used to determine the SOD activity in milk serum from 15 Swedish Red and White (SRW) cows and 18 Swedish Friesian (SF) cows at various stages of lactation. The XO activity in raw milk was also determined. The milk from these cows had a mean SOD activity of 0.83 +/- 1.14 U ml(-1) milk serum and a mean XO activity of 49 +/- 22 mU ml(-1) raw milk (n = 127). A difference between breeds could be noted in XO activity, ie milk from SF cows had significantly (P < 0.05) higher mean XO levels compared with milk from SRW cows, 54 +/- 23 mU ml(-1) than 44 +/- 21 mU ml(-1). A significantly increased level of XO activity in milk from SRW cows during the lactation was found. No significant effect of breed or stage of lactation on SOD activity could be detected. Individual cows with high and low milk SOD levels during the entire lactation have been identified.