The Quality Deterioration And Controlling Method Of Mulberry Leaf Vagetables After Harvest

Mulberry leaf vegetable,also known as mulberry sprout vegetable,is mainly composed of one bud and two leaves on the top of mulberry branch,among which mulberry leaf accounts for about 75%of the total mass.Mulberry leaf vegetable is a new type of vegetable that has sprung up in recent years,has not only been widely welcomed in the eastern and southern coastal areas,but also been valued by the relevant departments of the state.Mulberry leaf is a source of medicine and food,but the mature mulberry leaves have poor taste,so the tenderest part at the top of the branch serves as the edible part.It is because of their crispness and tenderness that mulberry leaf vegetables are prone to deterioration in the process of logistics preservation,such as wilting,browning,lignification,etc.Therefore,it is of great significance to develop appropriate preservation technology and study the quality deterioration and related mechanism in the preservation process of mulberry leaf vegetables for the maintenance of their edible value and commercial value.In this study,we first studied the quality change rule of mulberry leaf vegetables before commercial treatment,and then studied the effect of the vacuum precooling,simulated e-commerce packaging,and different packaging bags on the storage quality of mulberry leaf vegetables.The results are as follows:?1?The contents of soluble sugar,soluble protein,vitamin C and polyphenol decreased with the prolongation of mulberry leaf vegetables postharvest interval?1,2and 4 h?before commercial treatment,while the lignin content,hardness,membrane permeability and MDA contents increased gradually.The quality deterioration of mulberry leaf vegetables was enhanced with the increase of postharvest treatment interval,which was adverse to the quality maintenance during subsequent storage.After7 days storage,the soluble sugar content of samples in T₄ decreased by 19.85%comparing to T₁,while cell membrane permeability increased by 62.60%,and lignin content increased by 27.26%.According to correlation analysis,it was found that there was a positive correlation between lignin content and hardness,cell membrane permeability,as well as malondialdehyde accumulation.?2?The study found that the effect of vacuum precooling on the storage quality of mulberry leaf vegetable was double-sided.Lower precooling temperature?5??accelerated the quality deterioration of mulberry leaf vegetables after harvest,and was not conducive to storage and preservation;suitable precooling final temperature?15??could significantly delay the appearance quality of mulberry leaf vegetables,inhibit the respiration of mulberry leaf vegetables,and reduce the loss of nutrient value.At 96 h,the content of vitamin C and polyphenol in vacuum precooling final temperature at 15?was higher than that in vacuum precooling final temperature at 5?and CK?0.62mg/g vs 0.53 mg/g vs 0.56 mg/g;5.79 mg/g vs 4.89 mg/g vs 5.37 mg/g?.vacuum precooling combined with"foam box+ice bag"can extend the normal temperature logistics time to no less than 4 days.?3?It is found that vacuum precooling can keep the temperature lower for a long time,delay the decline of visual quality,reduce the loss of chlorophyll,vitamin C and other nutrients,inhibit the activity of peroxidase and laccase,and the accumulation of lignin,reduce the degree of membrane lipid peroxidation and membrane permeability of mulberry leaf vegetables,and thus delay the deterioration of mulberry leaf vegetables during shelf storage.Storage day 7,the lignin content of the control group reached7.42g/100g,which was 12.87%higher than that of the precooling group,and 58.85%higher than that of the 0 d group.the accumulation of lignin is one of the important factors to reduce the commercial value of mulberry leaf vegetables during storage.Vacuum precooling can inhibit the activity of peroxidase and laccase by inhibiting respiration,reducing the membrane damage and the degree of cell membrane lipid peroxidation,so as to reduce the accumulation of lignin in mulberry leaf vegetables.?4?Compared with MP20 bag packaging,PO bag packaging effectively inhibited the accumulation of lignin and hydrogen peroxide during storage at 25?.Storage day5,the content of lignin in MP20 bag was 165.23%higher than that in the 0th day,and25.10%higher than that in PO bag.PO bag packaging can delay the lignification of mulberry leaf by inhibiting the expression of PAL372,PAL341,4CL687,4CL358,POD475,LAC972,LAC969,LAC639 and other genes.Hydrogen peroxide can be used as a signal substance to regulate these genes,thus affecting the biosynthesis of lignin in mulberry leaf vegetables.PAL,4CL,CAD,POD and LAC are the key rate limiting enzymes in the biosynthesis of lignin in mulberry leaf vegetablesPrecooling or other commercial treatment being quickly conducted can effectively reduce the loss of storage quality of mulberry leaf vegetables.vacuum precooling final temperature at 15?can effectively delay the storage quality of mulberry leaf vegetables under simulated e-commerce logistics environment.The final temperature of vacuum precooling at 15?can effectively delay the accumulation of lignin and the decrease of nutritional quality.The accumulation of lignin is one of the main factors for the loss of commercial value of mulberry leaf vegetables under normal temperature storage.PO packaging can effectively delay the lignin content of mulberry leaf vegetable by inhibiting the expression of PAL,4CL,CAD,POD and LAC related genes.In order to delay the deterioration of storage quality and prolong the fresh-keeping period of mulberry leaf vegetables,the proper control of each stage after harvesting was carried out,which will help consumers to eat healthier and safer mulberry leaf vegetables while reducing the loss of commodity value in the process of logistics preservation of mulberry leaf vegetables,and provide theoretical and practical basis for standardized treatment of postharvest mulberry leaf vegetables.