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Received: 24 September 2014
Received in revised form: 12 November 2014
Accepted: 20 November 2014
Keywords
Polyphenol oxidase Round brinjal Characterization Inhibitor
Abstract
Polyphenol oxidase (PPO) catalyzes the conversion of phenolic compounds into o-quinones which will lead to food browning. This phenomenon causes huge implications on food industries, as it degrades food quality over time. By combining both ammonium sulphate precipitation and gel filtration chromatography, PPO was partially purified up to 5.26-fold with 11.23% yield. The enzyme activity was 5120 EU/mL using 4-methylcatechol as substrate. Maximal PPO activity was found at 30°C, pH 5.0 for 4-methylcatechol and 40°C, pH 6.0 for catechol. The PPO showed a higher affinity towards 4-methylcatechol but higher thermal stability when reacting with catechol. The Km and Vmax values were 5.00 mM, 2000 EU/ml for 4-methylcatechol and 10.79 mM, 526.32 EU/ml for catechol. Energy for inactivation (Ea) obtained using 4-methylcatechol and catechol were 12.57 kJ/mol and 14.23 kJ/mol from respective substrates. Sodium disulfite was a better inhibitor where 79.17% of PPO inhibition was achieved. The isolation and characterization of round brinjal PPO serves as a guideline to predict the behavior of enzyme, leading to effective prevention of its browning during processing and storage.
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Introduction
Round brinjal belongs to the family of Solanaceae and genus Solanum. This cultivar is categorized as S. melongena var. depressum, and is also known as dwarf brinjal (Choudhary, 1976). It is a perennial herbaceous plant with the height of 1.0 to 1.5 meter tall. The leaves have wool-like hairs underneath, and are broad and lobed, whereas the flowers are large and purple in color, despite vary morphologically depending on species (Bose et al., 2002).
Food browning embosses critical impact towards food processing industries as fruits and vegetables are susceptible to browning upon harvesting, followed by various postharvest activities (Gorny et al., 2002) This problem will lower the marketability, food value, and consumers' acceptability on the fruits and vegetables, affecting the economic situation of a country, especially to those rely on exporting unique and exotic harvest products that cannot be found elsewhere across the globe (Sapers and Miller, 1998; Gorny et al., 2000) Hence, it is crucial to understand the catalytic behavior of PPO using biochemical techniques in both enzyme extraction...