Effect of different precooling methods on precooling and quality of peeled lettuce during storage and transportation

Taking peeled lettuce as tested material,a contrastive analysis of different precooling methods was given,and the effect of different precooling methods on sensory quality,browning degree,chlorophyll content,PPO and POD activities and MDA content during storage and transport were investigated. The results showed that the key problem of peeled lettuce was browning,the storage and transport time of no precooling was only about 12h;the speeds of vacuum precooling and pressure-difference cooling were faster than other methods,while warming speeds were also faster,the browning couldn't be effectively prevented; the effect of ice and hydro cooling was similar and obvious,not only decreased the temperature,but also effectively blocked access to air( oxygen),thereby prevented the browning. The two methods could make the sensory quality obviously improved,the browning degree decreased significantly,the higher chlorophyll content maintained,and the rise of PPO and POD activities and MDA content slowed; the effect of ice cooling was better than hydro cooling for the peculiar smell,the storage and transport time of ice cooling could be prolonged to 24 h.Thus,the most suitable precooling method of peeled lettuce was ice cooling.