Phenylalanine ammonia lyase activity in fresh cut lettuce subjected to the combined action of heat mild shocks and chemical additives

Enzymatic browning reduces the visual quality of lettuce. In producing minimally processed lettuce, the stresses caused by wounding associated to cutting operations enhance enzymatic activity. Mild heat shocks with chlorinated water with calcium ions or ascorbic acid were assayed as a mean of reducing phenylalanine ammonia lyase (PAL) activity. Heat shocks reduced four times the rate of change in PAL activity during the first hours of storage over the rate for samples not subjected to thermal treatment. The addition of ascorbic acid resulted in an increase in PAL activity over samples where only chlorinated water was used. When calcium ions were introduced in the thermal baths, the PAL activity was reduced about four times, especially when the cutting operation was performed after the thermal shocks. Short heat shocks is a physical preservation technology that could be applied in countries with low technological development. This technology was efficient to control vegetable browning by reducing PAL activity.