Abstract: Taking catechol as substrate, polyphenol oxidase (PPO) activities in two hundred common wheat varieties were assayed by means of full-seed steeped in distilled water to extract PPO and measuring PPO activities by spectrophotometric methods. The results indicated that (1) frequency of varieties at different ranges of polyphenol oxidase activity showed skewed curve distribution, and top value trended to low polyphenol oxidase activity aside. (2) The variation of PPO activity was related to grain color and vitreousness. In red wheat, the rates of varieties with PPO activity above 100 AU·min-1·g-1 and 200.0 AU·min-1·g-1 were 31.82% and 11.63%, respectively. The variation of white wheat varieties was smaller than that of red wheat. The peak of PPO activity distribution curve in white wheat was close to 28.3 AU·min-1·g-1, and the rate of varieties with PPO activity above 100 AU·min-1·g-1 and 200 AU·min-1·g-1 were 10.40% and 0.06%, respectively. Generally, white wheat was significantly lower than those of red wheat in mean PPO activity and variety numbers with high PPO activity. (3) There was a high rate of low PPO activity varieties in white and chalky or half-vitreous wheat. (4) The variation among the Chinese commercial popular varieties in PPO activity was significant. Many white grain varieties from Huanghuai Wheat-growing Region had lower PPO activity (20～50　AU·min-1·g-1).

Key words: Common wheat, Varieties, Polyphenol oxidase, Variation