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. PPO_{S. melongenas}and PPO_{M. sapientum} gave different temperature and pH optima. The temperature-activity profile of PPO_{S. 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. PPO_S.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 PPO_S.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. PPO_S.melongenas and PPO_{M. 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.