Ascorbate Oxidase levels in Wheat and their Relationship to Baking Quality

Flour samples from 127 samples of wheat of 13 different cultivars grown throughout New Zealand during two seasons were extracted with 1mNa₂SO₄(pH 8·3) and assayed for ascorbate oxidase (AOX) at pH 6·2 by a continuous spectrophotometric method. The mean AOX activity of the cultivar with the greatest activity, Domino, was more than three times that of the cultivar with the lowest activity, Brock. The differences in AOX activity amongst cultivars were maintained for two seasons. The range of AOX activities of different wheat samples within each cultivar was about two-fold for most cultivars. A sample of cv. Domino with the highest activity was 14 times more active than the lowest activity sample of cv. Brock. There was a significant correlation between low AOX activity and bake score of cultivars or individual wheat samples. There was also a correlation between log AOX and protein content, and protein content was also correlated with bake score. Flour stored for 300 days at 20°C and wheat stored for two or more years had reduced AOX activities and bake scores. However, flour containing low endogenous AOX activity produced the same bake scores with ascorbic acid plus squash AOX as with ascorbic acid alone. It was concluded that the level of AOX in wheat was not critical to the ascorbic acid improver effect, provided sufficient oxygen was mixed into the dough by high-speed mixers.