Effect Of Cutting Styles And UV-C Treatment On Quality And Antioxidant Activity Of Fresh-cut Lettuce

Lettuce,which contains rich lettuce element,inorganic salt,vitamin and some trace elements such as zinc,iron,etc.,at the same time,because of its green,crisp and tasty sarcocarp,are favored by the vast number of consumers.Lettuce leaves easy to damage even rot,inner epidermis easy to lignify,so they are not resistant to store.Lettuce need to be peeled before eating,which is very suitable for fresh-cut processing.But lettuce after cutting treatment susceptible to microbes,and physiological and biochemical reactions intensify,thereby accelerating aging.Previous studies have shown that fruits and vegetables after the mechanical damage,the synthesis and accumulation of polyphenols will increase,the latter not only can resist external damage,but also can improve the oxidation resistance of fresh-cut fruits and vegetables.In addition,studies have shown that the appropriate dose of Ultraviolet-C(UV-C)is advantageous to the fresh-cut fruits and vegetables storage and fresh-keeping,and can effectively inhibit the growth of microor-ganisms during storage of fresh-cut fruits and vegetables,keep the better quality of fruits and vegetables.At the same time,UV-C is conducive to the synthesis of phenolics within certain radiation intensity,and improve the antioxidant activity of fresh-cut fruits and vegetables.But the effects of cutting style and UV-C treatment on quality and antioxidant activity of lettuce have not been reported.In this paper,the effect of the different doses of UV-C treatment on the quality,antioxidant activity and the fresh-keeping of fresh-cut lettuce were studied on the basis of comparing the effects of different cutting styles(slices,1/4 slices,and shreds)on the quality and antioxidant activity of fresh-cut lettuce.The mechanism of UV-C was discussed from the two aspects of phenylpropane and reactive oxygen metabolism,which provided the basis for the processing,fresh-keeping and scientific edible of fresh-cut lettuce.The results are as follows:1.The effects of different cutting styles on the quality and antioxidant activity of fresh-cut lettuce at 5 ?and 48 h were studied.Fresh lettuce was cut into slices,1/4 slices,and shreds,and the wonmding intensities of the three cutting styles were 5.7 cm/g,7.8 cm2/g and 13.6 cm2/g,respectively.The study showed that the fresh-cut processing could decrease lettuce's some quality indexes of lettuce such as the chlorophyll and ascorbic acid and so on,but the difference was not significant between the different cutting styles.The different cutting styles significantly increased the activity of PAL,and synthesis and accumulation of phenolics,as well as DPPH radical scavenging capacity of lettuce during storage.In addition,the cutting treatment also enhanced the activities of antioxidant enzymes such as SOD and CAT,and improved the antioxidant capacity of fresh lettuce.The total phenolic content and antioxidant activity of shreds lettuce were the highest at 24 h.These results demonstrated that cutting styles didn't have much effect on the quality,but significantly induced the synthesis of phenolic compounds,thereby improving the antioxidant activity of fresh-cut lettuce.2.The effects of different irradiation intensities(0,0.1,0.5,1.0 and 3.0 kJ/m2)of UV-C on the quality and antioxidant activity of fresh-cut shreds lettuce were studied.It was found that UV-C treatment could inhibit the growth of the total number of colonies of fresh-cut lettuce and browning,delay the decrease of chlorophyll and VC content,and improve effectively the content of phenolic compounds and DPPH radical scavenging capacity,and when the irradiation dose was 1.0 kJ/m,the effect is the best.The research results showed that UV-C treatment could effectively maintain the quality of fresh-cut lettuce and improve its antioxidant activity.3.The effects of UV-C treatment at 1.0 kJ/m2 on the phenylpropane metabolism and the reactive oxygen metabolism of fresh-cut lettuce were studied.It was found that UV-C treatment could effectively promote the activities of PAL,C4H and 4-CL in the phenylpropane metabolic pathway,increase the accumulation of phenolic compounds,inhibit the decrease of ascorbic acid and increase the DPPH free radical scavenging rate of fresh-cut lettuce.At the same time,UV-C treatment at 1.0 kJ/m2 could also regulate O2·-generation rate and the content of H2O2 by adjusting the activities of reactive oxygen metabolism related enzymes(SOD,CAT,POD,APX,etc.),alleviate the toxic effect of ROS on fresh-cut lettuce.