Effect of wounding on phenolic enzymes in six minimally processed lettuce cultivars upon storage

The effect of wounding on polyphenol oxidase (PPO), peroxidase (POD), and p henylalanine ammonialyase (PAL) was studied in six minimally processed lett uce (Lactuca sativa L.) cultivars upon storage for 7 days at 5 degreesC (Ic eberg Mikonos (IM), I. Green Queen (IGQ), I. Asdrubal (IA), Little Gem Sand ra (LGS), Romaine Cazorla (RC), and R. Modelo (RM)). Wounding of lettuce ti ssue midribs (because of minimal processing) caused an exponential increase in PPO activity due to the activation process from latent to fully active PPO by following first order kinetics in the time range from 3.7 days (LGS) to 6.3 days (RC). However, total PPO activity (active plus latent)remained constant. Isoform pattern of PPO changed upon storage probably because of posttranslational processes. POD activity linearly increased with induction of new POD isoenzymes. PAL activity presented a typical bell-shaped induct ion pattern in four cultivars. Only IM and IGQ showed a second induction re sponse which has not been previously described in the literature. IM was th e cultivar most susceptible to browning and RC was the cultivar least susce ptible. However, no clear correlation was observed between browning and any of the biochemical and physiological attributes investigated (PPO, PAL, an d POD activities, total and individual phenols accumulation, and ascorbic a cid content).