Studies On Phenolics,Antioxidant Capacity And Related Enzyme Activities In Pear During Fruit Development

Pear(Pyrus spp.)belongs to the Rosaceae family and is rich in nutritional and functional active ingredients,of which the phenolics are important functional active ingredients in pear fruit.In order to understand the distribution of phenolic substances and their changes during the development of pear fruits,the fruits of five pear varieties at different developmental stages were used as test materials in this study,the phenolic content,in vitro antioxidant capacity(ABTS~+radical scavenging ability,DPPH radical scavenging ability and FRAP)and related enzyme activities in the phenolic biosynthesis pathway(PAL,C4H,4CL,HCT,C3’H,HQT,CHS,CHI,IFS,F3H,FLS,DFR)of different fruit parts of Korla fragrant pear(peel,flesh,extra-kernel flesh and kernel)and whole fruits of Nanguo pear,Aksu Juju pear,Hongxiang pear and Luntai Juju pear were determined,and correlation analysis between pear fruit phenolics and enzyme activity was also carried out.The main findings are as follows:1.Distribution of phenolic substances and its change pattern during the development of pear fruit.During the development of pear fruit,the phenolic content of pear fruit showed a decreasing trend with slight fluctuations during the period,and 14 phenolic compounds were detected in all five types of pear fruit by HPLC,with arbutin and chlorogenic acid being the main monomeric phenolic fractions.(1)During the growth and development of pear fruits except for rutin,which was the highest in the fruit ripening stage,all other phenolic compounds,total phenol and total flavonoid contents were highest in the young fruit stage,and the total phenol and total flavonoid contents of young fruits of Korla fragrant pear picked in 2020,Korla fragrant pear picked in 2021,Nanguo pear,Aksu Juju pear,Hongxiang pear and Luntai Juju pear were 3.74 times and 4.04 times,4.34 times and 5.37 times,6.06 times and 9.56 times,6.98times and 14.57 times,4.76 times and 21.93 times and 4.45 times and 16.34 times respectively.(2)In the different fruit parts,the total phenol and total flavonoid contents of the two years harvested Korla fragrant pear fruits were as follows:kernel>peel>extra-kernel flesh>flesh,and the phenolic compounds were mainly distributed in the peel and kernel,with the richest phenolic compounds in the peel and the highest arbutin content,and the highest chlorogenic acid content in the kernel.(3)Among the different varieties,the Nanguo pear had the highest total phenolic and total flavonoid content with 9.63±0.91 mg GAE/g DW and 19.01±0.83 mg RE/g DW,respectively,followed by Korla fragrant pear picked in 2020 with mean values of 10.69±1.16 mg GAE/g DW and 10.69±1.69 mg RE/g DW,and Hongxiang pear was the lowest with mean values of 5.37 mg±0.45 GAE/g DW and 7.27±0.92 mg RE/g DW,in terms of monomeric phenolics,arbutin content was the highest in the Aksu Juju pear(6603.51μg/g DW)and chlorogenic acid content was the highest in the Nanguo pear(3269.32μg/g DW).2.Change pattern of antioxidant capacity during the development of pear fruit.During the development of pear fruit,DPPH,ABTS and FRAP methods were used to determine the antioxidant capacity of pear fruit,and the antioxidant capacity of pear fruit extract was comprehensively evaluated.The results showed that:(1)Throughout the growth and development period of pear fruits,except for the ABTS~+radical scavenging capacity and DPPH radical scavenging capacity of Korla fragrant pear fruits picked in 2020,which showed a rising and then decreasing trend,the three antioxidant capacities of Korla fragrant pear picked in 2021 and the other four types of pear fruits showed a wave-shaped decreasing trend.(2)In different tissue parts of pear fruit,the scavenging ability of Korla fragrant pear fruit extracts against ABTS~+free radicals was in the following order:peel>kernel>extra-kernel flesh>flesh;DPPH free radical scavenging ability and FRAP were consistent with the content of total phenols and total flavonoids.(3)Three antioxidant among the different pear varieties,the Nanguo pear was the highest and the Hongxiang pear was the lowest.3.Change pattern of enzyme activity related to the biosynthesis pathway of phenolic substances during pear fruit development.During the development of pear fruit,Using ELISA to determine the enzyme activity in the pear fruit phenolic synthesis pathway.The results showed that:(1)In the Korla fragrant pear,with the growth and development of the fruit PAL enzyme activity gradually decreased,CHI enzyme activity gradually increased,C3’H and C4H enzyme activity was first decreased and then increased,4CL enzyme activity first increased and then decreased,the rest of the seven enzyme activity showed“up-down-up”fluctuation trend;CHI enzyme activity in different fruit parts is the highest,followed by C3’H,PAL enzyme activity is the lowest,and FLS enzyme activity in the kernel of the fruit is the highest.(2)In the remaining four types of pear fruit,as the fruit ripened,there were two distinct peaks of C3’H enzyme activity in the middle(6/22to 8/6)and late(8/23 to 9/20)stages of development,with HCT enzyme activity showing a gradual increase and PAL enzyme activity showing a gradual decrease;C3’H enzyme activity was the highest and the PAL was lowest one,and C3’H enzyme activity was the highest in Hongxiang pear.4.Correlation analysis of phenolic substances,antioxidant capacity and enzyme activity in pear fruitThe correlation analysis of phenolics and antioxidant capacity,related enzyme activities using Genescloud revealed that:(1)In pear fruit,phenolics and related enzyme activities were correlated,and there was a highly significant positive correlation(p<0.01)between phenolics and the three antioxidant indicators for both different pear fruit parts and different pear fruit varieties,and differences in the degree of correlation between them indicate that it is feasible to use multiple indicators to determine the antioxidant capacity of pear fruit.(2)Phenols showed a highly significant positive correlation with PAL(p<0.01)and a highly significant negative correlation with 4CL(p<0.01)in different tissue parts of pear fruit.(3)For different pear fruit varieties,the phenolics showed a highly significant negative correlation with HCT(p<0.01).