Study On Preservation Of Leaf Vegetables By Vacuum Cooling Synchronously Coupled With Modified Atmosphere Technique

Leafy vegetables aged and rot easily due to their high water content and rapid respiratory metabolism after harvest.Hence,postharvest preservation is very important.As the the first step of cold chain,vacuum cooling technology can rapidly remove field heat and extend shelf life by evaporating the moisture of the product under vacuum.It is efficient,hygienic,and can get uniform temperature distribution.Vacuum cooling technology has great potential in the field of vegetable precooling.Modified atmosphere technology can control the respiration rate of fruits and vegetables through the establishment of low oxygen and high carbon dioxide gas atmosphere,and extend the shelf life of fruit and vegetables.In this study,the gas is discharged under vacuum condition,and then a specific mixture of oxygen,carbon dioxide and nitrogen into the vacuum chamber during the pressure recovery phase.Leafy vegetables?especially leaves?can retain gas,so synchronized cooling and modified atmosphere can achieve.On the basis of this vision,we set up a device platform to carry out relevant scientific and engineering experiments.In this paper,three kinds of leafy vegetables with different morphological structure,including cabbage?Brassica oleraceaL.var.capitata L?,Chinese cabbage?Brassica rapapekinensis?and flowering cabbage?Brassica campestris L.ssp.chinensis var.utilis Tsen et Lee?,were vacuum cooled under serial conditions of terminal pressure and load;the effects of appearance quality,nutritional quality and metabolic activity of leafy vegetables during cold storage were studied;The effects of synchronized cooling and modified atmosphere treatment then MAP?modified atmosphere packaging?on the quality of leafy vegetables were also studied.This paper focuses on the morphological factors and the spatial factors of leaf tissue space on the new type of synchronized cooling and modified atmosphere method.which provided scientific basis for the new method.The conclusions are as follows:1)Cabbage,chinese cabbage and flowering cabbage?2400?were quickly cooled,by vacuum cooling,to 4 oC in less than 25 min with terminal pressure of 500 Pa.The significant differences?P<0.05?in cooling time,weight loss and temperature difference among cabbage,Chinese cabbage,flowering cabbage were observed during vacuum cooling process at various pressures and weight loadings.The style and tightness of leaf wrapping of cabbages exhibited the large effects on the cooling time and temperature difference,while,the other tissue characteristics of leaf,including the non-vein ratio and the thickness appeared the large effects on the weight loss during vacuum cooling.The morphological structure of leaf is an important factor affecting the vacuum cooling process and theoptimal terminal pressure and weight loading during a vacuum cooling process depended on the morphological characteristics of a specific vegetable.2)Synchronized cooling and modified atmosphere treatment can reduce the rate of respiration,affect the activity of enzymes related to oxidative metabolism during storage,nutrition and appearance quality is better than control group.During storage for 9 days,the control group had lost the value of the product,while the treatment group had a commercial value at 15 days of storage.The size of the voids of the leaf tissue may have a greater effect on the gas retention during pressure recovery phase.3)Synchronized cooling and modified atmosphere treatment before MAP can effectively reduce the respiration rate of leafy vegetables,the respiration rate of the treatment group was 80.01% of that of the untreated group after 3 hours store;regulate activity of POD and CAT,delay the decline of sensory quality;decrease vitamin C and chlorophyll loss,after 12 days,the vitamin C content of treatment group cabbage was 13.28% higher than the group V_4?^500PaG^air>MAP_4?.