EVALUATION OF ELICITOR-INDUCED AND HIGH-PRESSURE-INDUCED ENZYMATIC BROWNING UTILIZING POTATO (SOLANUM-TUBEROSUM) SUSPENSION-CULTURES AS A MODEL SYSTEM FOR PLANT-TISSUES

Potato (Solanum tuberosum) suspension cultures were used as a model to obtain basic information regarding the occurrence of enzymatic browni ng reactions. The cultures were subjected to chitosan, an established stress factor, at concentrations from 2.5 to 100 mu g/mL to examine st ress reactions and to pressure treatments from 100 to 400 MPa for 10 m in at 25 degrees C to monitor the impact of minimal processing on plan t systems. The release of hydrogen peroxide from chitosan or high-pres sure-treated potato cells, which constitutes an initial stress respons e, was correlated with activities of phenylalanine ammonia-lyase (PAL) , peroxidase (PO),:and polyphenol oxidase (PPO) as well as with polyph enol production in cell free extracts. Chitosan-induced browning was r elated to PAL induction and corresponded to the concentration of pheno ls within the cells. Sensitivity of plant cells to these stress factor s was affected by the amount of PO present in the cells. High PO level s in the potato cells resulted in a fast degradation of hydrogen perox ide and reduced PAL induction after chitosan treatment. Different degr ees (reversible, irreversible) and locations (tonoplast, plasma membra ne) of permeabilization of cell membranes led to polyphenol production , which was correlated to reaction rates of PPO and increased pressure treatments. Pressures higher than 150 MPa resulted in irreversible pe rmeabilization of cell membranes and in loss of compartmentalization i n the cells.