PREDICTION OF POLYPHENOL OXIDASE ACTIVITY IN MODEL SOLUTIONS CONTAINING VARIOUS COMBINATIONS OF CHLOROGENIC ACID, (-)-EPICATECHIN, O-2, CO2, TEMPERATURE, AND PH BY MULTIWAY DATA-ANALYSIS

Controlled or modified packaging (CA/MA) of lettuce is simulated in mo del solutions containing lettuce polyphenol oxidase (PPO), chlorogenic acid (CG), and/or (-)-epicatechin (EPI) under various combinations of CO2, O-2, N-2, temperature, and pH conditions. Enzymatic browning is measured by PPO activity, color formation, substrate consumption, and development of products. Results were analyzed by multiway data analys is. CO2 minimized the chemical polymerization and reduced PPO activity slightly. CG was a better substrate for PPO than EPI. CG was, in part icular, involved in the primary enzymatic catalyzed oxidation, whereas EPI was important for the subsequent chemical polymerization in mixtu res of CG and EPI. A very descriptive five-parameter multiplicative mo del was obtained from the PPO data by the multivariate method PARAFAC. This model describes the importance of substrate, atmospheric composi tion, pH, and temperature for PPO activity. Low pH (3.0) reduced PPO a ctivity strongly (89%), whereas low temperature (5 degrees C) had a we aker effect on PPO activity (40% reduction of activity). The predictio n of PPO activity (O-2 consumption) by kinetic UV-vis spectra correlat ed well (r(2) = 0.87) with traditional polarographic PPO assay.