Modelling the degradation kinetics of vitamin C in fruit juice in relation to the initial headspace oxygen concentration

In the presence of oxygen, ascorbic acid (AA) is readily degraded to dehydroascorbic acid (DHA), which is prone to further degradation, hereby losing its vitamin C activity. In this study, the influence of different initial headspace O2 concentrations on the oxidation of AA and the subsequent formation and breakdown of DHA was investigated in a model fruit juice. Kinetic rate constants for solely AA degradation were estimated using zero and first order kinetics, while first order irreversible and reversible consecutive models were used to describe the degradation kinetics of AA combined with the oxidative formation and irreversible breakdown of DHA. A linear relationship was found between the first order AA degradation constants and the initial headspace oxygen concentrations. Further, a similar relationship was found for a commercial fruit juice. In this way a tool is provided to predict the AA content in fruit juices at different stages during storage, knowing the residual headspace oxygen concentration after packaging, the O2-permeability of the packaging material and the initial AA and DHA concentration.