Modelling ascorbic acid thermal degradation and browning in orange juice under aerobic conditions

Abstract

The thermal degradation of ascorbic acid (AA) in orange juice was analysed over in a 20–45 °C temperature range. Dehydroascorbic acid (DA), pH and browning were also monitored. Small amounts of AA degradation could be described by first order kinetics, but when only low amounts of AA were retained sigmoidal kinetics were clearly appropriate. The Weibull model was used to describe this pattern (R2adj > 0.995). The rate constant increased with temperature according to an Arrhenius‐type relationship. The activation energy was 38.6 kJ/mol and at the average temperature of the range tested, 32.5 °C, the rate constant was 64.4 × 10−3 h−1. The shape constant decreased linearly with temperature, from 2.17 to 1.13. Before the time when the maximum degradation rate occurred, pH, DA concentration and browning remained fairly constant, and then increased. It was found that this behaviour, as well as the dependence of the shape constant on temperature, might be explained by (i) the reconversion of DA into AA, following first order kinetics in relation to DA and second order kinetics in relation to AA, and by (ii) different sensitivities of the reaction rate constants to temperature. Browning was also well described by the Weibull model with a temperature independent shape constant.

The FAST index – A highly sensitive indicator of the heat impact on infant formula model

“…The activation energy was therefore calculated from the Arrhenius plot, including only the lower heat treatment assay as 67.94 ± 17.18 kJ/mol. Activation energies for vitamin C were higher than those reported in the literature, e.g., 9.5, 47.5 and 38.6 kJ/mol in a very simple amino acid, vitamin C and iron mixture at neutral pH (Bihel & Birlouez-Aragon, 1998), rose hip pulp (Karhan, Aksu, Tetik, & Turhan, 2003) and orange juice (Manso et al, 2001), respectively, the last two having lower pH, which prevents vitamin C from oxidation. In our experimental conditions strong losses of vitamin C were observed in a very short time, e.g., 23.3% after 9.5 min at 80°C and 56% after 3.5 min at 110°C.…”

“…The initial vitamin C concentration was 103.4 mg/l in the IF preparation. Vitamin C degradation complied with first-order kinetics as expected (Bendicho, Espanchs, Arantegui, & Martin, 2002;Bihel & Birlouez-Aragon, 1998;Burdurlu, Koca, & Karadeniz, 2006;Esteve et al, 1998;Manso, Oliveira, Oliveira, & Frias, 2001) and the first-order rates could be calculated from the slope of the Ln representation. However, above 100°C, the degradation was so fast that very low concentrations, at the limit of the method quantification level, were reached rapidly.…”

Thermal degradation kinetics of isoflavone aglycones from soy and red clover

“…Interestingly, a sigmoidal degradation course characterized by a linear period, a period of fast conversion and a final intercept of retardation has hitherto exclusively been reported for ascorbic acid degradation [28] and autocatalytic processes such as radical reactions during carotenoid decomposition [29]. Since the experiments of the present study were conducted on a similar molar basis, varying compound concentrations cannot be made responsible for the differing degradation patterns observed.…”

Ascorbic acid, aroma compounds and browning of orange juices related to PET packaging materials and pH

“…Manso et al 32 proposed a model which took account of the effects of temperature, pH and oxygen as well as the concentration of dehydroascorbic acid with respect to aerobic ascorbic acid degradation. In order to design their model, they experimentally monitored ascorbic acid degradation in juice under continuous oxygen aeration for periods up to 36 h. The next step in such a modelling approach could be to study a stored orange juice and to take account of both the aerobic (due to the oxygen permeability of plastic packaging materials) and anaerobic pathways.…”