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Thermal inactivation of pectin methylesterase, polygalacturonase, α-mannosidase, α-galactosidase and β-galactosidase activities in papaya (Carica papaya L. cv solo 8) pericarp

By: Benjamin N’zué Yao, Hubert Kouassi Konan, Clément Yao Yué Bi, Kablan Tano

Key Words: Thermal inactivation, Kinetic parameters, Carica papaya, Hydrolases activities

Int. J. Biosci. 9(4), 48-60, October 2016.

DOI: http://dx.doi.org/10.12692/ijb/9.4.48-60

Abstract

The effect of heat treatment on papaya (Carica papaya cv solo 8) pericarp Pectin methylesterase (PME), Polygalacturonase (PG), α-mannosidase (α-MAN), α-galactosidase (α-GAL) and β-galactosidase (β-GAL) activities were studied over a range of 40 to 65 °C. Denaturation of these enzymes, measured by the loss in activity, could be described as a first-order reaction with k-values between 0.0011 and 0.0303 min-1. D- and k-values decreased and increased, respectively, with increasing temperature, indicating fast enzymatic inactivation at higher temperatures. Results suggested that PME, PG, α-MAN, α-GAL and β-GAL are the relatively thermostables enzymes with a Z-value of 34.84, 19.12, 31.54, 42.69 and 17.69 °C respectively and Ea value of 39.90, 105.93, 64.38, 47.28 and 91.46 kJ mol-1 respectively. The Gibbs free energy ΔG values range from 89.21 for α-GAL to 102.95 kJ/mol for α-MAN at 40-65 °C. The results of the thermodynamic investigations indicated that the hydrolytic reactions were: (1) not spontaneous (∆G > 0), (2) slightly endothermic (∆H > 0) and (3) reversible (∆S < 0). However, Positive values of entropy (ΔS > 0) for PG indicated that this enzyme is found in a chaotic state at the end of the reaction. The high value obtained for the variation in enthalpy indicated that a high amount of energy was required to initiate denaturation, probably due to the molecular conformation of these enzymes.

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