Thermal and pH stabilities of partially purified polyphenol oxidase extracted from Solanum melongenas and Musa sapientum fruits

Abstract

Enzyme activity depends largely on environmental conditions such as temperature and pH. The stability 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. melongenasand 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, at 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. Key words: Polyphenol oxidase, temperature, pH, Solanum melongenas and Musa sapientum.