87 Variation in polyphenol oxidase activity of wheat, using an improved assay method.

W. J. LEE (1), D. R. Shelton (2), and M. Kim (3). (1) Department of Food Science, Kangnung National University, Kangnung, Korea; (2) Department of Agronomy, University of Nebraska, Lincoln, NE 68583-0915; (3) Department of Biometry, University of Nebraska, Lincoln, NE 68583-0712.

Polyphenol oxidase (PPO) has been implicated in darkening reactions that limit the acceptability of wheat-based end use products, such as Asian noodles. A rapid screening method of measuring PPO activity was developed. Freshly prepared L-DOPA solution was added to wheat seeds (0.4 g, crushed with a pliers), incubated for 5 min at 37 C and filtered through a syringe filter (25 mm cellulose acetate, 0.2 µm). Absorbance of the reaction solution was measured at 475nm. Two sets of wheat samples were measured for PPO activity. Sample set 1 was 8 hard red winter wheat genotypes harvested in 1996–1998 from three locations in Nebraska. Sample set 2 consisted of 4 hard red winter wheat and 1 hard white wheat that were harvested in 1998 at five locations in Wyoming. Variety and location had a significant effect on grain PPO activity in wheat samples. PPO activity was significantly influenced by the interaction of variety and location. The relationship of wheat PPO activity to the color of grain and flour and the color change of Asian noodles was determined.