Thermal and pH stabilities of partially purified polyphenol oxidase extracted from <i>Solanum melongenas</i> and <i>Musa sapientum</i> 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 preincubated 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. PPO_{S. melongenas} and PPO_{M. sapientum} gave different temperature and pH optima. The temperature-activity profile of PPOS. melongenas and PPO_{M. sapientum} showed a strong positive correlation (r = 0.907363). At pH = 10.0, PPO_{M. sapientum} activity represented 65.3% decay in enzyme activity, whereas PPO_{S. melongenas} represented 79.3% decay in enzyme activity. PPOS.melongenas and PPO_{M. 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 PPO_{M. sapientum} showed a strong positive correlations under the same experimental thermal conditions, with exception at 20°C (r = 0.693375). Specifically, pre-incubation of PPO_M.sapientum for t = 90 min at 60°C caused 18.4% decay in relative activity of PPO_{M. sapientum}. At t = 90 min, pre-incubation of PPO_{M. sapientum}, at pH = 3.5 caused decay in activity within the range of 30.8-36.1%, whereas PPO_{M. 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.

Keywords: Polyphenol oxidase, temperature, pH, Solanum melongenas and Musa sapientum.

African Journal of Biotechnology Vol. 12(38), pp. 5688-5694