β-Carotene and Capsanthin Co-oxidation by Lipoxygenase. Kinetic and Thermodynamic Aspects of the Reaction

Abstract

Carotenoid pigment co-oxidation by lipoxygenase has been studied by factorially combining three pigments: β-carotene, capsanthin, and diesterified capsanthin; two environmental conditions: presence or absence of light; three oxidant conditions in the same reaction medium: presence of both lipoxygenase and linoleic acid, presence of linoleic acid only, and absence of both; and four temperatures: 15, 25, 35, and 45 °C. Independently of the presence or absence of enzyme, diesterified capsanthin and β-carotene were the most unstable pigments, and both exhibited similar lability, although nonesterified capsanthin showed a great stability. This different behavior among pigments could be related with their polarity. The overall reaction clearly follows a first-order kinetic model and the thermodynamic parameters reveal that the co-oxidation reactions of carotenoids are multiple isokinetic forms of just one reaction. In all of the cases studied, enzymatic or nonenzymatic decoloring of carotenoids is a theoret...