EFFECT OF HIGH CO2 ON PHENOLICS CONTENT A ND THE ACTIVITY OF PHENYLALANINE AMMONIA-LYASE IN ROMAINE LETTUCE

The role of phenol metabolism in the development of brown lesions (BL) on the midrib of Romaine lettuce (Lactuca sativa L.) leaves stored un der high CO2 was assessed. The leaves were stored for 7 d at 4-degrees -C under a continuous stream of air or CO2 (15%) in air, then transfer red to air at 20-degrees-C for two days. Results indicate thal the dev elopment of BL under CO2 at low temperature was not related to the act ivation of phenylalanine ammonia-lyase (PAL). However, after aeration of the product, BL symptoms increased with the phenol content of tissu es. Phenolic compounds analysis of the midrib showed the presence of c hlorogenic, gallic, protocatechuic and gentisic acids. The data sugges t that the regulation of phenol synthesis, particularly chlorogenic ac id by CO2, involves the regulation of other enzymes than PAL, later in the phenylpropanoid pathway.