Effects Of Refrigeration And1-methylcyclopropene On The Metabolic Of Volatile Aroma In Nanguo Pear And Control

Nanguo Pear (Pyrus ussuriensis Maxim) grows mainly in the Liaoning province. It is normally harvested in September with green and hard flesh, less juice and no odor. When it is completely ripe, the fruit is juicy with a soft and smooth flesh, golden color, sour-sweet taste, and an aroma that welcomed by most consumers. This study focused on the change of aroma-related compounds of Nanguo pear which were treated with1-MCP and refrigeration at harvest. However, it has been reported that both1-MCP and refrigeration have effect on the specific aroma in Nanguo pear. Nanguo pears were used as the raw materials, and change of aroma during the shelf life in Nanguo Pear after cold storage and1-MCP treatment was studied. In addition, the activities of lipoxygenase, hydrogen peroxide repressible enzyme, pyruvatedecarboxylase, alcoholdehydrogenase and alcohol acyltransferase were investigated because they were associated with the formation of volatile compounds. The determination of esters volatiles in the refrigerated Nanguo pear treated with1-MCP, and the study of the effect of ethephon, salicylic acid and methyl jasmonic acid on volatile compounds could provide the scientific basis for developing new technology in Nanguo pear or other fruit preservation.The main results were as follows:1. The simultaneous distillation extraction (SDE) method detected volatile substances which had less species and lower percentage than solid phase microextraction (SPME) method. SPME analysis can extract many volatile components and they can represent the typical aroma in Nanguo pear. The extraction temperature and time were set at50℃and40min, respectively. The concentration of NaCl was0.32g·mL-1and the rotor rpm1000r·min-1. The result indicated that the main aroma components were ethyl acetate, ethyl butyrate, ethyl caproate, hexyl acetate, and a-farnesene.2. The content of esters in Nanguo pear was10.51%after3months refrigeration and17.89%after5months refrigeration which was lower than in CK fruits. The content of esters in fruits treated with1-MCP was9.58%and it was lower than that of untreated fruits. The content of esters in Nanguo pear treated with1-MCP was24.15%during the best edible period after3months refrigeration and36.42%after5months refrigeration which was lower than in CK fruits. The results showed that1-MCP had inhibition the formation of esters in fruits, especially1-MCP combined refrigeration has significant inhibition effect on aroma in Nanguo pear. The main effects of1-MCP on esters in refrigerated Nanguo showed that it inhibited the synthesis of ethyl acetate, butanoic acid ethyl ester, hexanoic acid methyl ester, hexanoic acid ethyl ester, hexanoic acid ethyl ester but promoted the synthesis of acetic acid heptyl ester.Compare with natural ripe at room temperature in Nanguo pear after harvest, the isoleucine, cysteine and leucine contents increased during the best edible period in Nanguo pear after cold storage, while the levels of alanine, valine and methionine decreased. In Nanguo fruit treated with1-MCP during shelf life at room temperature after harvest and cold storage, the total amino acid was significantly higher than CK and the aroma was obviously lighten after1-MCP treatment. It showed that there was no direct relationship between amino acid metabolism and the lightened aroma after1-MCP and refrigeration treatment.The contents of linoleic, linolenic acid and the activities of LOX, HPL, AAT which are the key enzyme related aroma synthesis significantly reduced after refrigeration and1-MCP treatment. This change matched the pattern of aroma that was lightened after cold storage and1-MCP treatment, and inferring refrigeration and1-MCP inhibited aroma components formation mainly through inhibiting the fatty acid synthesis and inactivating PDC, HPL and AAT.Refrigeration and1-MCP had no significant effect on the contents of glucose, fructose and sucrose in Nanguo pear, but the treatments significant reduced the activity of AAT in the process of ester substances generated glycometabolism. Therefore, refrigeration and1-MCP treatment weakened the aroma components mainly through inhibiting the key enzyme in the process of ester substances generated glycometabolism.4. Exogenous ethylene treatment (2mmol/L) had better effects for maintaining aroma quality in Nanguo pear fruit during the shelf-life after cold storage. The ethylene exhibited weaker ability in recovering Nanguo pear aroma with the increasing of refrigeration time.5. Compared with salicylic acid and methyl jasmonate treatments, ethephon can effectively increase ACS activity. So the increasing of ethephon level would finally increase ester content in Nanguo pear which was treated with1-MCP and stored for3months and led to strong aroma of the fruit.We can therefore concluded that the effect of refrigeration and1-MCP on the aroma in the Nanguo pear was via the fatty acid biosynthesis pathway which was related to the inhibition of the activity of LOX, HPL, PDC, and AAT. Ethephon can effectively increase the recovery ability of aroma components of Nanguo pear.