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 thermal degradation of vitamin C of marula, mango and guava pulp at different heat treatments at temperature ranging from 80 to 150 degrees C were investigated. For temperatures lower than 125 degrees 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 vitamin C degradation as biphasic behaviour was observed. Therefore the model was transformed in a two-fraction model in which the vitamin C content is divided in relatively stable and instable fractions. Manila had a low k(d1,100 degrees C) of 7.2 x 10(-3) min(-1) compared to k(d1,100 degrees C) of 1.2 x 10(-1) min(-1) for guava and 1.3 x 10(-1) min(-1) for mango. Guava had the highest activation energy, E-a of 58 kJ/mol, followed by mango with 39 kJ/mol and then manila with 29 kJ/mol. (C) 2012 Elsevier Ltd. All rights reserved.