Study On The Mechanism And Regulation Of Core Browning Of �Nanguo' Pears At Ambient Temperature Based On Membrane Lipid Metabolism

�Nanguo' pear(Pyrus ussuriensis Maxim.)is one of the specialty fruits in Liaoning Province.The main producing areas are Anshan and Haicheng.�Nanguo' pear is usually harvested in the first and middle of September,and the harvested �Nanguo' pears can be stored at ambient temperature for about half a month.During storage,with the ripening and aging of the fruit,the core is prone to browning,which affects the commodity value of �Nanguo' pears.Therefore,studying the occurrence and mechanism of core browning of �Nanguo' pears at ambient temperature is of great significance for exploring browning regulation technology.This study first analyzed the browning of different parts of �Nanguo' pears and related changes in physiological and biochemical indicators during the post-ripening process at ambient temperature after harvest.From the perspective of membrane lipid metabolism,butyl alcohol treatment was used to inhibit PLD activity.The effects of membrane lipid metabolism on the core browning of �Nanguo' pears at ambient temperature were studied by analyzing the occurrence of core browning,membrane lipid component and its content,the activities of key enzymes in membrane lipid metabolism and the expression of related genes.Based on the above studies,the regulatory effect of 1-MCP treatment on the core browning of �Nanguo' pears after harvest was explored.The main results are as follows:Under ambient temperature conditions after harvest,with the extension of storage time,the firmness of �Nanguo' pears gradually decreased,while the soluble solids gradually increased.The browning of the core began to occur on the 11 th day,and increased with the prolonged of the storage periods.At 15 th day,the flesh appeared slight browning,and no browning symptoms appeared in the pericarp during this period.The analysis of browningrelated indicators in different parts of the fruit showed that the total phenol content and PPO activity were the highest,the pericarp was second,and the flesh was the lowest;the relative conductivity and MDA content of the core tissue were also significantly higher than those of the pericarp and flesh.It indicatied that core tissue is the main part of browning of �Nanguo' pears at ambient temperature,and it is related to the abnormal physiological metabolism of the tissue.The treatment with butyl alcohol as a PLD inhibitor showed that the activity of PLD and LOX and the expression of related genes in the core tissue were significantly dropped,the changes in the content of membrane lipid components were slowed,the changes in the membrane lipid component were slowed down,and the relative content of linoleic acid and linolenic acid unsaturated fatty acids was alleviated,and the accumulation of relative content of unsaturated fatty acid oleic acid,saturated fatty acid stearic acid and palmitic acid was reduced.In addition,the treatment also inhibited the increase of cell membrane permeability and the accumulation of MDA content.Under the transmission electron microscope(TEM),the cell structure of the control fruit was gradually disintegrated during the ambient temperature storage,while the cell structure of the treated fruit was well preserved.At the same time,the core browning time of �Nanguo' pears was significantly delayed,and the browning rate and browning index were also significantly reduced.The treatment of PLD inhibitor proved that the core browning of �Nanguo' pears at ambient temperature was closely related to the membrane lipid metabolism.Therefore,the inhibition of membrane lipid degradation and maintenance of membrane lipid components,membrane system structure and functional stability are essential important.After 1-MCP treatment,the post-ripening process of �Nanguo' pears was significantly delayed,the core browning of the fruit was delayed for 30 days,and the increase in browning rate and browning index were significantly reduced.Different from the control,the MDA content of the fruit in the treatment group maintained a low level,the rising rate of relative conductivity was significantly delayed.When stored for 15 th day,the total membrane lipid content,MGDG content,and PA,PC,PE,PI,PS,LPC and LPG content of the treatment group were significantly higher than those of the control group,and the relative contents of linolenic acid and linoleic acid were also higher than those in the control group.Compared with the control group,the peak of PLD and LOX activity was not significantly different,but the time of the peak appeared to be significantly delayed.The expression of Pu PLD?4 was significantly increased in the treated and control fruits at the later stage of storage.However,the up-regulated expression time of Pu PLD?4 was significantly delayed and the expression level was significantly lower than that of the control.The peak of Pu LOX expression level was significantly delayed and the peak value was significantly reduced.On the 15 th day,the cell structure of the control fruit was almost disintegrated,but the cell structure of the treated fruit was still intact.In conclusion,1-MCP treatment effectively delayed the post-ripening process of the fruit,maintained the stability of membrane lipid components and membrane system in the core tissue,thereby delayed the occurrence of core browning at ambient temperature.