PHYSIOLOGICAL ATTRIBUTES RELATED TO QUALITY ATTRIBUTES AND STORAGE LIFE OF MINIMALLY PROCESSED LETTUCE

Relationships between storage quality attributes, such as russet spott ing and browning intensity, and physiological attributes, such as solu ble phenolic content and polyphenol oxidase (PPO) and phenylalanine am monia-lyase (PAL) activities, of minimally processed crisphead lettuce (Lactuca sativa L.) were studied. The processed lettuce tissue was ke pt in air or air plus ethylene at 2 or 5 mul.liter-1 at 2.5 or 5C for 1 to 4 days and then transferred to air at 2.5,5, or 20C for 1 to seve ral days. None of the above physiological attributes of the initial sa mples from eight lettuce cultivars (Calmar, El Toro, Sea Green, Pacifi c, Monterey, Salinas 88, 86-13, and Nerone) and three maturity stages (immature, mature, and overmature) correlated with their storage quali ty. However, ethylene-induced PPO and PAL activities and browning inte nsity measured 3 to 4 days after harvest consistently and significantl y correlated with the final visual quality of the ethylene-treated, mi nimally processed lettuce after 6 to 10 days of storage. Among these t hree attributes, ethylene induced a 2.5- to 5.3-fold increase in PAL a ctivity, while the relative changes in PPO activity and browning inten sity were only 23 % to 68 %. Ethylene-induced PAL activity possibly ma y be used as an index to predict the storage life of minimally process ed lettuce.