This paper is the first study on the inhibition and thermal inactivation of polyphenol oxidases (PPO) from the heart of Mediterranean palm (Chamaerops humilis L.). PPO was extracted and purified, and its physicochemical properties, kinetic parameters of inhibition in the presence of a non-toxic sulfhydryl amino acid (L-cysteine), and parameters of thermal inactivation were determined. The PPO catalyzed the oxidation of 4-methyl catechol and pyrogallol as substrates but did not affect tyrosine. The best substrate was 4-methylcatechol. Enzyme activity decreases when pH decreases, and the optimal pH is 6.8. PPO enzyme activity was inhibited by citric acid, sodium fluoride, and L-cysteine, the most effective and non-competitive type inhibitor. The optimal temperature of the enzyme was 35°C, and thermal stability was measured at 45°C, 55°C, 65°C, 70°C, 75°C, and 80°C. The half-life values of PPO were 92.4, 38.07, 25.16, 2.26, 0.43, and 0.42 min, respectively. The D and activation energy values show that the PPO from the Mediterranean palm heart is very sensitive to temperature change. Its activity decreases rapidly above 40 and 70°C. At 75°C, 2 min is enough to reduce the enzyme activity to 10% of the initial value. The present study concludes that the enzymatic browning of Mediterranean palm hearts can be reduced by thermal treatment, pH adjustment, and non-toxic sulfhydryl amino acid (L-cysteine).
Key words: Polyphenol oxidase (PPO); Mediterranean palm heart (Chamaerops humilis. L); nontoxic inhibitor, thermal inactivation, enzyme characterization.
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