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American Journal of Plant Physiology
Year: 2013  |  Volume: 8  |  Issue: 2  |  Page No.: 63 - 73

Thermal and pH Stabilities of Partially Purified Polyphenol Oxidase Extracted from Solanum melongenas and Musa sapientum Fruits

P.C. Chikezie, A.R. Akuwudike and C.M. Chikezie    

Abstract: Enzyme activity depends largely on environmental conditions such as temperature and pH. The stabilities of Polyphenol Oxidase (PPO) extracted from Solanum melongenas and Musa sapientum fruits pre-incubated in varying thermal and pH conditions were carried out. Enzyme activity was measured by spectrophotometric methods. The reaction mixture contained 3.5 mL of 0.20 M phosphate buffer (pH = 6.8), 1.0 mL of 0.75 mM catechol and 0.5 mL of enzyme solution. PPOS. melongenas and PPOM. sapientum gave different temperature and pH optima. The temperature-activity profile of PPOS. melongenas and PPOM. sapientum showed a strong positive correlation (r = 0.907363). At pH = 10.0, PPOM. sapientum activity represented 65.3% decay in enzyme activity, whereas PPOS. melongenas represented 79.3% decay in enzyme activity. PPOS. melongenas and PPOM. sapientum stability at pre-incubated temperatures of 20, 50 and 60°C and pH values of 3.5, 6.0 and 8.0 were measured. Residual activities of PPOS. melongenas and PPOM. sapientum showed a strong positive correlations under the same experimental thermal conditions, with exception at 20°C (r = 0.693375). Specifically, pre-incubation of PPOM. sapientum for t = 90 min at 60°C caused 18.4% decay in relative activity of PPOM. sapientum. At t = 90 min, pre-incubation of PPOM. sapientum, in pH = 3.5 caused decay in activity within the range of 30.8-36.1%, whereas PPOM. sapientum pre-incubated in pH = 6.0 and pH = 8.0 gave decay in activity within the range of (1.5-9.8%) and (2.7-6.5%), respectively. PPOS. melongenas and PPOM. sapientum showed relatively higher stabilities as the incubation pH tended towards alkaline conditions, whereas the two experimental temperatures (20 and 60°C) promoted destabilization.

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