ABSTRACT

Polyphenol oxidase (PPO) is a biological catalyst responsible for the oxidation of phenolic compounds in some plants, seafood, causing enzymatic browning and melanin formation in the skin. In this study, PPO was extracted from the pulp of tamarind (Tamarindus indica L.) and partially purified by an ammonium sulphate precipitation method. The crude PPO was characterized in terms of, temperature, pH, and kinetics. The results show that PPO exhibits maximum activity at pH = 7.0 and temperature 30oC in the presence of catechol as substrate. The kinetics of the enzymatic reaction was followed and determined spectrophotometrically. The specificity of tamarind PPO towards different substrates was studied using catechol, gallic acid, and hydroquinone as sources of phenolic compounds. The results showed that the enzyme has higher affinity and specificity for catechol followed by hydroquinone and gallic acid. Using Michelis – Menten model, the kinetic parameters, (Km and Vmax) were determined, and the values of these parameters were as follow: 12.33 mM and 0.125 au/min for catechol, 33.23 mM and 0.121 au/min for hydroquinone 23.37 mM and 0.115 au/min for gallic acid. The results showed that ascorbic acid suppressed PPO activity more than EDTA and the percentage inhibition was calculated as 70% for ascorbic acid and 45.5% for EDTA. On the other hand, metal ions were found to increase the enzyme activity. Regarding enzyme stability of tamarind PPO, it was clear that the PPO activity decreased with increasing temperature, as the protein denatured and thus lost its catalytic property. Keywords: Polyphenol oxidase, Oxidation, Substrate, Inhibitor
Publication date: 01/09/2022

https://ijbpas.com/pdf/2022/September/MS_IJBPAS_2022_6365.pdf

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https://doi.org/10.31032/IJBPAS/2022/11.9.6365