Assay Of Polyphenol Oxidase Activity In Wheat And Their Relationship With Dough Sheet Color

Total 72 wheat samples were selected to measure flour color, protein content, grain hardness, yellow pigment content and changes of dough sheet color over time in two years. The results showed as follows: 1. There was significant difference among wheat varieties in change rate of dough sheet color over time. 2. The color of dough sheets were high correlated with protein content, yellow pigment content and PPO activity. Protein content was one of most important factors and its correlation coefficients with 0 h,24 h dough brightness L* were -0.85 and -0.65, respectively. Yellow pigment content was high significantly correlated with dough sheet a* and b*.Its correlation coefficients with 0 h a*, 24 h a*, 0 h b*, 24 h b*were -0.58 , -0.44, 0.88 and 0.71, respectively. Dough sheet 0 h L*had no significant correlation with PPO activities,however,after storage 24h, PPO activities obtained by using different methods were significantly or high significantly correlated with dough sheet L*(the correlation coefficients -0.32～-0.47). This suggested that PPO activities were the most important factor causing discoloration of dough sheet during storage. PPO activities were not significantly correlated with dough sheet a*,b* at several hours of storage, but high significantly after 4h. 3.There were signicant correlations between many quality characteristics and whole-seed, flour PPO activities .The results showed that grain hardness and flour yield had significant correlation with PPO activities,however, PPO activities were not significantly correlated with protein content yellow pigment content and test weight. 4.There were signicant or high significant correlations among whole-seed, wholemeal and flour PPO activities measued by using L-DOPA as substrate. However, the correlations among PPO activities measued by catechol as substrate were not high signicant. Compared between PPO activities tested by different substrate, the most significant correlations were obtained between whole-seed PPO activities, then wholemeal, last flour. The reason might be that the range and variation coefficient of flour PPO activities measued by catechol as substrate were smaller. Wholemeal or whole-seed assays were easy for microanalysis and this is very important for rapid screening wheat germplasm for PPO activity.