Extraction and properties of Douglas-fir sapwood polyphenol oxidase Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9w0325660

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  • Chemical stains that develop on commercial woods are problems of great economic importance. The polyphenol oxidases catalyze the oxidation of the phenolics that naturally exist in plants to quinones when the cell structure is disrupted. The quinones produced are further oxidized and polymerized to melanin, the pigment which is responsible for brown discoloration. The objectives of this study was to extract and characterize the activity of polyphenol oxidase (PPO) enzyme, that naturally exists in the sapwood of Douglas-fir {Pseudotsugamenziesii (Mirb.) Franco}. The enzyme catalyzes the oxidation of some endogenous phenolics found in the sapwood which act as a substrate, when the cell structure is disrupted and exposed to air, humidity and warm weather. The specifity of PPO toward substrates and the effect of PH, temperature and inhibitors on it's activity were examined. Prevention of PPO activity loss during storage of the fresh Douglas-fir sapwood was possible by sealing in oxygenimpermeable plastic bags, and storing at -25°C. Crude extraction of PPO was from fresh sapwood using potassium phosphate buffer. No phenolic scavenger was added. Another extraction was done from an acetone-insoluble powder and polyethylene glycol was added as a phenolic scavenger. This extract did not show enhanced enzyme activity relative to the first one. The PPO has two pH optima for activity one at pH 5.5 and one at pH 8.0. Using 4-methylcatechol as a substrate, the one at pH 8.0 was 31% higher than the one at pH 5.5. The optimum temperature that gave the highest PPO activity was 35°C when 4-methylcatechol was used as a substrate. No activity for monophenol substrates was detected for the extracted PPO. The highest activity detected was for (-)-epicatechin, dihydroquercetin and 4-methycatechol in decreasing order of activity. Soluble polyvinypyrrolidone inhibited the enzyme reversibly and Tween 80 and Monawet BM-45 successfully reactivated the enzyme. Phosphoric and citric acids inhibited the enzyme but no attempts to reactivate it were made.
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