Study On The Effects Of Three Enzymes On Postharvest Ascorbic Acid Metabolism Of'Hayward' And'Huate' Kiwifruit

As one of the fruits with high ascorbic acid content,kiwifruit is popular among the public,but its loss of AsA during storage and transportation is serious,and the loss is as high as 50%,which seriously affects the nutritional value of the fruit.'Walter,kiwifruit is a new breed selected by Chinese scientists from the wild resources of A.eriantha Ben-tham.The AsA content is as high as 800-1000 mg/100g,and the loss after harvest is small.Postharvest AsA content of the main cultivar 'Hayward,kiwifruit in China is 90-120 mg/100g,and the AsA content in the post-fruit ripening period drops to 40-60 mg/100g,and the loss is as high as 50%.Therefore,reducing the loss of AsA in Postharvest Ripening Period of kiwifruit is an urgent problem to be solved in scientific research and production of kiwifruit.In this paper,'Hayward' and'Walter' kiwifruit were used as experimental materials to study the changes of quality,AsA,total ascorbic acid(T-AsA)and dehydroascorbic acid(DHA)in the storage of two varieties of fruits at room temperature(25oC)after harvest.The enzyme-linked immunosorbent assay was used to study the differences in the activities of four enzymes,namely,dehydroascorbate reductase(DHAR),ascorbate oxidase(AO),ascorbate peroxidase(APX)and laccase(Laccase),which affect AsA content.Real-time fluorescence quantitative PCR was used to study the gene expression differences of AsA-related enzymes in two Kiwifruit cultivars,in order to provide a theoretical basis for the systematic study of AsA metabolic mechanism of kiwifruit after harvest and the development of new storage technology to reduce AsA loss.The main results and conclusions are as follows:(l)'Walter' kiwifruit is more resistant to storage than 'Hayward' kiwifruit,with a small change in hardness,low soft rot rate,and higher titratable acid content than,Hayward' kiwifruit,but the soluble solid content was lower than the 'Hayward,kiwifruit in the later stage of storage,The total sugar-acid ratio was lower,the taste and flavor were not as good as the 'Hayward' kiwifruit,and the edibility was poor.(2)Differences in AsA,DHA,T-AsA,T-AsA/DHA between two cultivars of kiwifruit after harvest:The AsA content of 'Hayward' kiwifruit was 86.9 mg·100g-1FW(formula weight)at the early postharvest stage and the loss was about 45%at the end of storage,but the content of AsA in 'Walter' kiwifruit was higher at the beginning of harvest,which was 610 mg·100g-1FW,and it increased to 886 mg·100g-1FW in the medium term,reaching the peak value,and declined to 778 mg·100g-1FW at the end,higher than the first day after postharvest.AsA content,the overall upward trend;The DHA content of the two varieties of kiwifruit decreased as a whole during the whole storage period,but the DHA content of 'Hayward' kiwifruit was always lower than that of the 'Walter' kiwifruit;The change trend of T-AsA content was similar to that of AsA content;The AsA/DHA ratio of 'Hayward' kiwifruit was much lower than that of 'Waiter' kiwifruit during the later storage period.(3)Changes of DHAR,Laccase,AO and APX activities in two Kiwifruit cultivars after harvest:DHAR is the key enzyme for AsA regeneration.On the 11th day after harvest,the DHA content of 'Walter' kiwifruit reached a peak value of 2.67 U.g-1FW,which was significantly higher than that of 'Hayward' kiwifruit;The correlation analysis showed that the change of AsA content in 'Walter' kiwifruit was significantly correlated with DHAR,the correlation coefficient was 0.993,while the change of AsA content in 'Hayward' kiwifruit was not significantly correlated with DHAR;The Laccase activity in the two kiwifruit varieties was 'Hayward' higher than'Walter' during the whole storage period,and negatively correlated with the AsA content of the kiwifruit of each species;AO activity was higher in 'Hayward' than'Walter' from the 11th day after harvest.The correlation analysis showed that there was a significant negative correlation between AO activity and AsA content in two varieties of kiwifruit;The APX activity of'Haywardr kiwifruit was lower than that of'Walter' kiwifruit during the whole ripening period,and the difference of APX activity between the two varieties was small from the 6th day after harvest,and there was no significant correlation between APX activity and AsA content.Based on this,it is speculated that AO and Laccase are the main reasons for the decrease of AsA content in 'Hayward' kiwifruit after harvest.(4)Differences of Laccase,AO and APX gene expression between two varieties after harvest:Real-time fluorescence quantitative PCR was used to study the difference of gene expression.It was found that Achn007661 in the Laccse gene family differed greatly in the two varieties.The expression of 'Hayward' kiwifruit Achrn007661 was 5.8 times higher than that of 'Walter' kiwifruit after 16 days storage.The expression of Achn007661 was negatively correlated with AsA content of'Hayward' kiwifruit and 'Walter' kiwifruit,with correlation coefficients of 0.947 and 0.950,respectively;The expression of Achn020161 in AO gene family was significantly different between the two cultivars.Achn020161 in 'Hayward' kiwifruit was 6.2 times higher than that in 'Walter' kiwifruit after 16 days storage.Achn020161 was negatively correlated with AsA content in 'Hayward' kiwifruit and 'Walter'kiwifruit,with correlation coefficients of 0.922 and 0.920;It is speculated that Achn020161 in the AO gene family is also a key gene leading to the oxidation of AsA;The three genes of the APX gene family,Achn123021,Achn082241,and Achn187071,have a certain effect on the change of AsA content,but it is not a key gene for oxidative degradation of AsA.