Phenylalanine ammonia lyase activity in minimally processed Romaine lettuce

The effect of the intensity of damage on the phenylalanine ammonia lyase (PAL) activity, on browning of midrib tissue and on the overall visual quality (OVQ) of minimally processed Romaine lettuce was studied. In highly wounded leaves two peaks of PAL activity were observed. In whole and in less-damaged leaves only one peak was detected. The rate of change in PAL activity during the first day of storage was found to be related to the intensity of damage. Browning in midrib tissue developed in the most highly damaged leaves after 4 days of storage. Dehydration and wilting reduced the OVQ of lettuce before the onset of browning and the occurrence of peaks in PAL activity.