Study On Effect Of Ultrasound Combined With Dimethyl Carbonate On The Quality And Safety Of Fresh-cut Lettuce

Lettuce,with its fragrant and crisp taste and rich nutritional value,is becoming increasingly popular as a vegetable.Fresh-cut lettuce for its healthy,convenient features has gradually become the main product of the fresh-cut industry.However,due to the larger surface area,high water content and leaf tissue crispness,it was susceptible to injury after picking,coupled with the cutting of inflicting wounds,fresh-cut lettuce was prone to browning and microbial infections that affect their quality and safety,and ultimately result in shortened shelf life.In this paper,fresh-cut lettuce as the object of research was studied from the perspective of physics and chemistry to probe the ultrasound and dimethyl carbonate treated separately and combined treatment on their quality and safety,which can provide the theory basis for fresh-cut lettuce industrialization.1.In order to study the effects of ultrasonic conditions on the quality and safety of lettuce,single factor tests were conducted to select orthogonal experimental factors used total bacteria count and the number of E.coli as indicators.The orthogonal experiment was conducted used total bacterial count as a indicator to find out the optimum condition,then investigated the changes on the quality and microorganisms of lettuce product treated under the optimal ultrasonic condition during preservation.According to the result of orthogonal design experiment,the order of affecting experiment was as follows:ultrasonic time>ultrasonic power>ultrasonic temperature and the suitable condition was:lettuce was treatmented under 240W for 10min at 20? in which case,its shelf life was extended 6 days comparing with the control.2.The effects of sterilizing conditions of dimethyl carbonate on the quality and safety of lettuce was studied,single factor tests were conducted to select orthogonal experimental factors used total bacteria count and the number of yeast and molds as indicators.The orthogonal experiment was conducted used total bacterial count as a indicator to find out the optimum condition,then investigated the changes on the quality and microorganisms of lettuce product treated under the optimal sterilizing condition during preservation.According to the result of orthogonal design experiment,the order of affecting experiment was as follows:DMDC concentrations>sterilization time>solid-liquid ratio,the final selection of the optimum conditions for sterilization:DMDC concentration 200mg/L,sterilization time 10min,solid-liquid ratio of 1:15,in this condition microbial of lettuce was significantly reduced.3.The effects on quality and safety of fresh-cut lettuce of ultrasonic disinfection combined with chemical fungicide dimethyl carbonate was studied.Lettuce was treated under the optimum ultrasonic condition and DMDC sterilization condition on the basis of the research in the second and third capters.Used the bacterial count and number of yeast and molds as microbiol indexes,chlorophyll.vitamin C and sugar content as quality indexes and peroxidase and polyphenol oxidase as physical indexes to evaluate the effects on the quality and safety of fresh cut lettuce of the saperate and combined treatment The results showed that the content of vitamin C?chlorophyll and sugar of the combination group was enhanced 9.1%?24.7 and 12.5%compared with the control group.And the ultrasonic technology combined with dimethyl carbonate can effectivaly reduce the number of microorganisms and inhibit the activity of POD.PPO and CAT.