Physiological Characteristics And Quality Changes Of Postharvest Allium Mongolicum Regel By Pre-Cooling And Modified Atmosphere Packaging During Low Temperature Storage

Allium mongolicum Regel is a leafy vegetable grown in desert,sandy land and arid mountain slopes,and is preferred by people in Inner Mongolia,Xinjiang and Ningxia.Due to the high moisture content,vulnerable to mechanical damage and other characteristics,Allium mongolicum Regel is prone to get dried,wilting and rot after harvest,which leads to short shelf life and restricted market development.Therefore,this research took Allium mongolicum Regel as the object to explore the changes of physiological characteristics and quality after harvest.The effects of vacuum pre-cooling,different temperature and modified packaging on the physiological characteristics and quality were investigated.The physiological characteristics include respiratory intensity,catalase activity（CAT）,peroxidase activity（POD）,polyphenol oxidase activity（PPO）and cellulase activity（CE）,and the quality indicators include sensory evaluation,weight loss rate,chlorophyll and vitamin C.The purpose of this study was to elucidate postharvest physiology and the effects of combined storage method on physiological characteristics and quality changes of Allium mongolicum Regel,and to provide theoretical basis and technical reference for storage and transportation of it.The main research conclusions are as follows:Shelf life of Allium mongolicum Regel under indoor temperature（11±1℃）was7 d.During storage,sensory evaluation scores decreased rapidly.Allium mongolicum Regel is the type of vegetables with respiratory climacteric,and the peak of respiration occurs at the 4th day of storage,with respiratory intensity of 83.32 CO₂mg/（kg?h）.High respiratory intensity consumes more nutrients,such as chlorophyll and vitamin C which decreased by 63.48%and 76.26%at the end of storage,respectively.CAT activity decreased gradually and POD activity firstly increased and then decreased.PPO activity was higher than similar leaf vegetables,so degree of browning was higher.Through the detection of the above indicators,it is found that the post-harvest Allium mongolicum Regel has strong respiration and rapid water loss,fast decline of commodity value,which are similar to leeks after harvest.Therefore,the storage method of Allium mongolicum Regel is combining vacuum pre-cooling and modified atmosphere package,referring to the storage methods of leeks and its physiological characteristics.Determination of vacuum pre-cooling optimal parameters and effect of vacuum pre-cooling on of Allium mongolicum Regel under low temperature storage:Orthogonal experimental design were used in the vacuum pre-cooling process with four factors and three levels.Four factors included treatment time,treatment capacity,sprinkling amount and coating method.Results showed that treatment time of 8 min,treatment capacity of 150 g,sprinkle water of 10%and water absorbing film coated were optimum condition for pre-cooling.Weight loss rate and final temperature was1.92%and 4.3℃respectively optimal conditions of vacuum pre-cooling.Both the pre-cooling group and the control group（direct cryopreservation without pre-cooling）lost their commercial value at the 13th day of storage.During this period,the respiratory peak of the two groups appeared on the 7th day.The respiratory intensity of the pre-cooling group was lower than the control group,and the difference was the largest on the 9th day,when the respiratory intensity of pre-cooling group was only61.23%of that of the control group.CAT activity,POD activity and PPO activity of control group were higher than pre-cooling group.At the end of storage,the weight loss rates of the pre-cooling group were 42.69%.The loss rate of chlorophyll was10.28%and that of vitamin C was 24.79%,which were significantly lower than control group（50.18%,57.02%,44.73%）.The results showed that vacuum pre-cooling could effectively inhibit the respiration,reduce the loss of nutrients,slow down the increase of browning degree,and improve the storage quality of Allium mongolicum Regel.Different storage temperature（0℃,4℃and 10℃）on Allium mongolicum Regel during storage after pre-cooling:According to the results of sensory evaluation,the shelf life was 13 d under 0℃and 4℃and 9 d under 10℃.During this period,the occurring of respiratory peak of Allium mongolicum Regel under 4℃storage was the latest,and the intensity was 57.35 CO₂ mg/（kg?h）,which were lower than that of other groups.The respiratory intensity were 112.26 CO₂ mg/（kg?h）and146.42 mg/（kg?h）under 0℃and 10℃,respectively.CAT and POD activity were the highest in 10℃and the lowest in 4℃.PPO activity is significantly lower than other groups in 4℃.Weight loss rate is significantly higher than that of other two groups in 10℃group,and in the late storage 4℃group had significantly lower weight loss rate that 0℃group.The chlorophyll and vitamin C content are declining,but 4℃group had lowest loss rate.So low temperature（0℃and 4℃）can inhibit the respiration of Allium mongolicum Regel and nutrients consumption,but some indicators represent poor effect at 0℃,and 4℃is optimum storage temperature for Allium mongolicum Regel.The treatment groups of modified atmosphere packaging were MAP1with 5%O₂,15%CO₂,80%N₂,MAP with 28%O₂,20%CO₂,72%N₂,MAP3 with 10%O₂,10%CO₂,80%N₂,and control group（CK）with 21%O₂,1%CO_2,78%N₂（air ratio）.According to the results of sensory evaluation,the storage cycle of Allium mongolicum Regel was 13 days.During this period,MAP2 maintained a high score,while the score of CK group was lower in the early and late stages of storage.The weight loss rate of Allium mongolicum Regel under MAP and CK condition was significantly lower than that in the unpackaged groups.MAP delayed the emerge of respiratory peak and reduced the respiratory intensity.The respiratory intensity of MAP2（47.59 CO₂ mg/（kg?h））was lower than that of other groups.Compared with three MAP groups,CAT activity of CK group was higher in the early stage of storage,and decreased rapidly in the later stage.For three MAP groups,PPO activity of MAP1 was the highest and that of MAP2 was lowest.During the whole storage period,the content of vitamin C of MAP1 and MAP3 was lower than that of MAP2,and the decrease rate of vitamin C for MAP2 was the lowest,which were 68.15%.Oxygen content decreased more slowly in MAP2,indicating Allium mongolicum Regel had less time for suffering anaerobic respiration.Therefore,MAP has a significant positive effect on reducing the weight loss rate,but does not extend the shelf life.It only improved the storage quality in the early stage of storage,but failed to have a positive effect on the storage quality in the later stage.The results suggested that the sealed environment leads to the inability of evaporation of water,which eventually accumulates at the bottom,providing a suitable condition for the growth and reproduction of microorganisms.In the future,it can be considered to adopt different storage methods in different stages,such as adopting MAP in the early stage of storage and direct cryopreservation in the later stage...