Preliminary Study On Polyphenol Oxidase In Common Wheat Variaties

Polyphenol oxidase(PPO) is a kind of protease connecting Cu elements, which widely exists in animal, plant and micro-organizm. PPO catalyzes phenolic compounds to conversion to o-quinones in presence of molecular oxygen. The o-quinones react with amines or thiol groups to product melanins, and affect quality of products. The physiology function of PPO is not well understood. There is some PPO in wheat grain, it mainly affects the whiteness of flour and flour base products in processing and storage of wheat. The darkening phenomna of such products may reduce consumer acceptance and decrease quality of the produacts. As a result, much more attention shoud be paid to PPO in wheat quality improvement.Three experiments on the method of measuring polyphenol oxidase activity, the distribution of PPO in difference tissues or organs of wheat plants, and the variation of PPO in common wheat varieties were conducted. The remits showed as the follows:1 Research on methods of measuring polyphenol oxidase activity in wheat kernel: Using catechol as substrate, the absorbance changes of water extract derived from soaking the full seeds for 25 hours were measured at 405nm to express polyphenol oxidase (PPO) activities. The formation of reaction product was rapid in initial 5 minutes and the differences among wheat cultivars were remarkable. Soaking time has a significant effect on PPO activity Soaking for time less 20 hours, there were no apparent differences of PPO activities in cultivars, but beyond 30 hours, self absorbance of enzyme liquid increased rapidly. Therefore, soaking for 25-30 hours was adequate for measuring PPO activities in wheat cultivars and the optimal temperature and pH value for PPO activity test were about 35℃ and 6.0 respectively.2 Distribution of PPO in wheat plant: polyphenol oxidase (PPO) in different tissues or organs of wheat plant was determined. The results showed that the distribution of PPO was different, PPO activities were higher and the patterns of isoenzyme were richer in tender parts, and PPO activities descended from the top to the bottom ( flag leaf > kernel > ear stem > 2nd internode > 3nd internode > root> 4nd internode ). Nine bands of PPO isoenzymeof PPO isoenzyme patterns were found in kernel, indicating more isoenzymes in immature kernel than other parts .3 The Variation of Polyphenol Oxidase Activity in Common Wheat Varieties: Taking catechol as substrate, polyphenol oxidase (PPO) activities in 200 common wheat varieties were assayed by the 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 range of polyphenol oxidase activity showed skewed curve distribution, and top value trended to low polyphenol oxidase activity side. (2) The variation of PPO activity was correlated to grain colour and vitreousness. Generally, PPO activity in red wheats was higher than that of white wheats. (3) There was high ratio of low PPO activity varieties in white and chalky type. (4) The differences of PPO activities among Chinese commercial wheat varieties were significant. The selection and use of low PPO activities wheat germplasms would be benefit to future wheat quality improvement. (5) Some genetic germplasms were selected in order to research on PPO in wheat.