Kinetics of thermal degradation of Vitamin C in Marula Fruit (Sclerocarya birrea subsp. caffra) as compared to other selected tropical fruits

The kinetics of the thermaldegradation of vitaminC of marula, mango and guava pulp at different heat treatments at temperature ranging from 80 to 150 °C were investigated. For temperatures lower than 125 °C, the ascorbic acid in marula pulp was about 15 fold more stable to heat than the ascorbic acid in mango and guava pulp. The results showed that a simple first order degradation model could not describe the vitaminCdegradation as biphasic behaviour was observed. Therefore the model was transformed in a two-fraction model in which the vitaminC content is divided in relatively stable and instable fractions. Marula had a low kd1,100°C of 7.2 × 10-3 min-1compared to kd1,100°C of 1.2 × 10-1 min-1 for guava and 1.3 × 10-1 min-1 for mango. Guava had the highest activation energy, Ea of 58 kJ/mol, followed by mango with 39 kJ/mol and then marula with 29 kJ/mol.