Study On The Browning Inhibition Of Ethanol And Deoxygenation Treatment On Iceberg Lettuce

Iceberg lettuce is one of the daily edible vegetables,crisp and tender,with high medicinal value and edible value,loved by consumers.In addition,young people’s increasing respect for new consumption methods such as lettuce salad also promotes the rapid growth of lettuce production and demand.However,the crisp and tender characteristics of iceberg lettuce make it vulnerable to mechanical damage during picking,transportation and storage.The damaged part will browning quickly,which will affect its appearance.When damage is inevitable,it is very important to study the browning inhibition technology of damaged lettuce for the healthy development of lettuce industry.At present,there is a lack of research on the inhibition of damaged lettuce browning from the physiological point of view;The mechanism of ethanol fumigation inhibiting the browning of damaged lettuce was discussed from the aspect of antioxidant enzymes;Then the effect of oxygen concentration on the browning of lettuce was studied;Finally,the antibrowning and quality protection effects of deoxidizer controlled oxygen and ethanol fumigation on damaged lettuce were discussed.1.To study the antibrowning effect of different ethanol concentration and different ethanol fumigation time on lettuce,and the inhibition effect of ethanol fumigation on the damaged lettuce at different time points of logistics.The results showed that ethanol treatment could effectively inhibit the browning of damaged lettuce,and the effect of ethanol fumigation on the browning of damaged lettuce at 200-800μL/L within this concentration range,with the increase of ethanol concentration,the effect of inhibiting browning is better,but 800μL/L ethanol can accelerate the aging and softening of lettuce,500μL/L is the best concentration for comprehensive preservation;In 1-3 h fumigation time,the increase of fumigation time was conducive to the maintenance of L*value and overall sensory,but there was no significant difference between 2 h and 3 h fumigation time（P>0.05）;At 500μL/L fumigation 2 h after 4 h,14 h,24 h of lettuce artificial damage,found that 4 h and 14 h group of brightness value,hardness and sensory quality to maintain better,24 h group is not good,indicating that ethanol treatment can effectively control the lettuce after transportation for a period of time due to damage caused by browning.2.500μL/L ethanol fumigation inhibited the browning of damaged lettuce,and explored the anti browning mechanism of ethanol fumigation on damaged lettuce.The results show that 500μL/L ethanol fumigation can reduce the activity of phenylalanine ammonia lyase,reduce the accumulation of total phenols in browning substrate generated by phenylalanine ammonia lyase pathway,maintain the high POD,CAT,APX in lettuce,mainly control the activities of lipid peroxidase and active oxygen metabolism enzymes,reduce the production rate and conductivity of superoxide anion,reduce the accumulation of malondialdehyde,and maintain the integrity of cell membrane,so as to effectively control the browning of damaged lettuce.3.After fumigating with two good ethanol concentrations of 500μL/L and 800μL/L respectively,the head lettuce plastic bag was packaged and punched（to keep the oxygen in the bag always controlled at about 20%）and not punched（to make the bag oxygen is in a medium and low oxygen environment）to explore the influence of oxygen concentration in the bag on browning of damaged lettuce after fumigation.The results showed that,compared with the perforated group,the non porous group with two fumigation concentrations could control lettuce browning,inhibit PPO and PAL enzyme activities,reduce total phenol production,and prevent the decrease of brightness（L*）.Due to the increased respiration after the lettuce was damaged,anaerobic respiration occurred in the non porous group with two fumigation concentrations during the middle and late storage,and some lettuce in the bag softened.The formation rate of O₂^-and electrical conductivity increased significantly,and the content of MDA increased sharply.Based on the above two results,in the process of logistics packaging,the damaged lettuce should be kept in a low oxygen environment as far as possible,but at the same time,the anaerobic environment in the packaging should be avoided.4.Based on the above conclusions,the advantage of the mechanical damage can be avoided by the cushioning of the foam box.When adding different quality deoxidizer in the foam box at the time of packing,the initial oxygen ratio in the box will be reduced,and the possibility of controlling the browning of the damaged lettuce with the combination technology of deoxidizer control and ethanol treatment is studied.The results showed that hypoxia（16 bags of deoxidizer）could inhibit browning,inhibit PPO and PAL enzyme activities to the greatest extent,reduce the production of total phenols,reduce browning index,superoxide anion production and respiratory intensity,increase the activities of POD,SOD,CAT and other antioxidant enzymes in lettuce,and maintain the marketability of lettuce to the greatest extent.This indicates that the combination of deoxidizer control and ethanol fumigation can effectively control the browning of damaged lettuce,and the use of foam box can avoid the problem of anaerobic respiration during the late storage period of lettuce.Therefore,it is an effective and feasible combination technology to inhibit browning of lettuce logistics after adding alcohol to fumigation,packing with foam box and packing proper amount of deoxidizer before packaging.