Analysis Of The Cuticular Wax Components Of Munage Grape And Its Effect On The Storability Of Fruit

Munage grape（Vitis vinifera L.cv.Munage）is a characteristic grape fruit in Xinjiang,which is favored by many consumers because of its thin skin,juicy,sweet and sour taste.However,the quality problems such as water loss,wilting and rotting are very likely to occur during the storage and transportation of post-harvest Munage grapes.As a natural protective layer,plant cuticular wax covers the plant surface,and its special biological function is closely related to the quality of fruits and vegetables after harvest.The surface of Munage grape contains white plant cuticular wax,but its effect on the storage quality of Munage grape is not clear.Therefore,this study used mature Munage grape as raw materials,using organic solvent immersion method to extract fruit cuticular wax,and combined with response surface methodology to optimize the extraction process of cuticular wax;Using gas chromatography mass spectrometry（GC-MS）to detect and analyze the cuticular wax components of Munage grape,and adopting scanning electron microscopy（SEM）to identify and analyze the cuticular wax structure;After removing the wax from Munage grapes pericarp,the effects of cuticular wax on the quality changes of Munage grape fruit were investigated by analyzing the physiological related indicators,reactive oxygen species（ROS）related indicators,and the microstructure of pulp cells of the dewaxed fruit.The results are as follows:（1）The single factor test showed that dichloromethane was the best extraction agent,followed by n-hexane.When the solvent mixing ratio was 3:1（m L/m L）,the liquid material ratio was 2:1（m L/g）,and the extraction time was 6 min,the wax extraction amount was the highest.Based on the single factor experimental results,the response surface optimization obtained the optimal wax extraction process as follows:the mixture ratio of dichloromethane and n-hexane solvent was 3:1（m L/m L）,the liquid-to-material ratio was 2:1（m L/g）,and the extraction time was 7.5 min.Under this condition,the extraction amount was 43.60±1.04 mg·100g^-1,which was only 0.98%from the predicted value of response surface,indicating that the wax extraction process is reasonable and reliable,and has reference value.（2）The cuticular wax components of Munage grape were mainly composed of fatty acids（58.06%）,esters（10.22%）,hydrocarbons（7.03%）,aldehydes（6.04%）,alcohols（4.93%）and terpenes（3.24%）.There were 61 compounds in total,including 13 fatty acids,12 alkanes,1 olefin,10 alcohols,9 esters,5aldehydes,4 terpenes and 7 unclassified substances.The main compounds include palmitic acid,stearic acid,heptadecane,and decadecane,etc.Meanwhile,through SEM,it was found that the microstructure of the cuticular wax of the Munage grape was similar to the plate-like shape of the leaves,and the edge was irregular serrated,which was vertically embedded on the surface of the grape.The formation of this plate-like wax structure may be mainly influenced by the fatty acids in the wax components.（3）The removal of the wax from Munage grapes pericarp accelerated the yellowing,decay,weight loss and respiratory metabolism of the fruit,causing quality deterioration.On the 40th day of storage,the b^*value,decay rate,weight loss rate,respiratory rate and ethylene production of the fruit in the dewaxing group were 6.64%,15.51%,14.29%19.76%and 13.81%higher than control group,while the hardness and SSC of the dewaxed fruit were 23.66%and 3.56%lower than those of the control group,respectively.The dewaxed fruit had a greater impact on the respiratory intensity,ethylene release and SSC of the fruit.Wax removal had great influence on b^*value,decay rate,weight loss rate,and ethylene production.In addition,the antioxidant content and antioxidant enzyme activity of the dewaxed group fruits were lower than those of the control group in the later stage of storage,and the O₂^·-(585.19 nmol·min^-1·g^-1)production rate and H₂O₂(525.15μmol·kg^-1)content were higher on the 40th day of storage,as well as the cell membrane lipid peroxidation and cell structure damage were more severe.So removing wax reduces the antioxidant capacity of the fruit,which may be one of the factors contributing to the decrease in storage quality of the dewaxed group.To sum up,the cuticular wax can effectively maintain the post-harvest quality of grape fruit and enhance the storage capacity of grape fruit by maintaining the metabolic balance of ROS in grape fruit.