Evaluation of elicitor- 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 browning reactions. The cultures were subjected to chitosan, an established stress factor, at concentrations from 2.5 to 100 mu g/mL to examine stress reactions and to pressure treatments from 100 to 400 MPa for 10 min at 25 degrees C to monitor the impact of minimal processing on plant systems. The release of hydrogen peroxide from chitosan or high-pressure-treated potato cells, which constitutes an initial stress response, was correlated with activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO),:and polyphenol oxidase (PPO) as well as with polyphenol production in cell free extracts. Chitosan-induced browning was related to PAL induction and corresponded to the concentration of phenols within the cells. Sensitivity of plant cells to these stress factors was affected by the amount of PO present in the cells. High PO levels in the potato cells resulted in a fast degradation of hydrogen peroxide and reduced PAL induction after chitosan treatment. Different degrees (reversible, irreversible) and locations (tonoplast, plasma membrane) 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 permeabilization of cell membranes and in loss of compartmentalization in the cells.