| Chestnut has a wide planting area in China.In order to improve chestnut economical benefit,China has begun the exploration on the study of chestnut processing products.However,the chestnut browning is always affecting the quality of products.Polyphenol oxidase?PPO?,which is rich in chestnut nuts,is a kind of protease mixed with Cu element and has the ability to catalyze the oxidation reduction reaction of hydroxy phenols to generate melanin.And it is main driver of enzymatic browning and has negative effect on the quality of chestnut processing products.To prevent such effect on browning of chestnut,we have developed a variety of methods,including chemical methods,physical methods,molecular biology methods,genetic methods.Among them,Genetic methods are catching more and more attention in the breeding sector and expected to make improvements in varieties of chestnut essentially.However,the relationship between PPO activity and browning of chestnut has not been studied from the perspective of species difference,making the breeding of fine varieties fail to effectively expand.Through exploration of chestnut browning and PPO activity assay method and 37 kinds of chestnut varieties in both the determination and screening results showed as follow.?1?PPO activity of chestnut was measured using a spectrophotometer method at 410 nm wavelength taking catechol as substrate.From the start to the first period of 5 minutes,it showed fastest response and large differences among varieties.After 5 minutes,the reaction tends to smoothly decline.When Chestnut PPO activity was detected,the most optimum pH value was adjusted to 6.5 and the optimum temperature was 30 ?,PPO activity was expressed as ?A·U·min-1·g-1.Chestnut browning reaction,The most suitable conditions for three days at 4 ?.More than three days,Browning has stabilized.Browning measurement value is measured using a spectrophotometer at a wavelength of 420 nm.The experimental data obtained in this experiment were used for further research.?2?When Browning occurred,Varieties range of variation of 0.044 at the initial browning.Difference interval of browning final value was 0.284-0.751,ranged from 0.467.Variation interval of browning was 0.151-0.600,varying in the range of 0.449 with Significant difference?P < 0.05?.Browning chestnut varieties final value distribution is unimodal.The largest number of species in the 0.5-0.6 range.There were a few varieties with the relatively low final browning value.More varieties were observed with browning change value in 0.3-0.4 and 0.4-0.5 range.Most of the Chestnut varieties did not have strong anti-browning abilities.A few varieties of anti-browning strong or weak.?3?Difference of PPO activities among different varieties of chestnut were observed,with variation interval were 8.53-149.48 U·min-1·g-1 and amplitude in the range of 140.95 U·min-1·g-1.Overall significant difference were observed among varieties?P<0.05?and PPO activity of most varieties had unimodal distribution.And PPO activity of the vast majority of Chinese chestnut varieties were 20-40 U·min-1·g-1 while there are fewer varieties of chestnut with relatively low PPO activity.?4?Analysis of relationship between PPO activity and browning among chestnut varieties showed that PPO activity had the most relevant relationship with browning changes value whereas the least with browning initial value.The comparison between PPO activity and browning change value showed that with the increasing degree of browning chestnut,PPO activity increased.PPO activity of chestnut was positively correlated with the degree of browning.Only part of the chestnut varieties had high PPO activity,but it had a smaller degree of browning.This showed that the PPO activity had influence on browning of chestnut.The more active PPO activity was,the greater degree of browning the chestnut had.?5?chestnut PPO activity could be divided into five categories using cluster analysis.PPO activity in the range of all types,first type of PPO activity was 8.53-22.63 U·min-1·g-1,the second category was 26.46-45.61 U·min-1·g-1,third category was 53.24-71.89 U·min-1·g-1,fourth type was 94.20-113.30 U·min-1·g-1,fifth type was 125.78-149.48 U·min-1·g-1.As a result,the varieties with low PPO activity and browning resistance were sorted and they were ‘Heishanzhai 7',‘Quanjiao 3,'‘Yanhong',‘Hebei Zunyu',‘Yanguang 3'.And the chestnut varieties with different PPO activity and browning resistance were divided to provide the basis for breeding. |
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