BIOCHEMICAL-CHANGES INVOLVED IN BROWNING OF GAMMA-IRRADIATED CUT WITLOOF CHICORY

The increasing browning phenomenon of cut witloof chicory (Cichorium i ntybus) irradiated with a dose of 3 kGy and stored five days at 10 deg rees C was investigated in relation to total phenolic concentration, p henylalanine ammonia-lyase activity, total and reduced glutathione con tent, polyphenol oxidase and peroxidase activities. Phenylalanine ammo nia-lyase activity underwent a strong activation with a maximum on the second day of storage, and total phenolic compounds tended to accumul ate from the third day. Glutathione content was monitored as indicator of antioxidant capacities. Total glutathione decreased by 25% after i rradiation and was restored on the third day of storage, while the 50% decrease of reduced glutathione was maintained along the five days. C onversely, a 30% inhibition of polyphenol oxidase and peroxidase activ ities occured after irradiation. We concluded first that irradiation-i nduced browning of cut chicory may be due to both an increase of pheno lic metabolism and a reduction in antioxidant capacities, and second t hat increased membrane permeability may allow substrate-enzyme contact .