Effect of water activity on autoxidation of raw peanut oil

The effect of water activity (a w ) on rate of autoxidation of raw peanut oil at 37 C was studied. Up to 3 weeks of storage, no marked effect of a w on the rate of peroxide formation was noticeable. However, with prolonged storage, the rate of peroxide formation decreased rapidly at a w of 0.67 and higher as compared to a w of 0.50 and lower. At the end of 9 weeks’ storage, the peroxide value at a w =0.02‐0.50 was in the range of 31–35, while it was only ca. 10 at 0.79 and 0.92 a w . There was no noticeable influence of a w on the rate of free fatty acid formation. The oil stored for 7 weeks at 0.02 and 0.11 a w had fresh flavor, although the peroxide values were high; whereas the oils at 0.79 and 0.92 a w were stale, although the peroxide values were less than 10. The anisidine value at 0.02 a w (348) was higher than at 0.92 a w (62). The carbonyl values at 0.02 and 0.11 a w were also higher (1090, 1021) than at 0.79 and 0.92 a w (573, 780). The results indicate that the protective effect on the oil against peroxide formation at high a w may be due to certain components present in raw peanut oil.