Abstract:
Orange is one of the important fruit crops around Jimma town and the juice from orange fruit is one of the natural good antioxidant sources due to the presence of ascorbic acid (vitamin C). The objective of the present work was to assess the degradation kinetics of ascorbic acid in orange fruit starting from farm to consumer under different storage conditions around Jimma town (Ascolla, Dedo; Alemayehumecha, Yebu) using random nano/hole p-phenylenediamine film grafted glassy carbon electrode. The anodic peak current for ascorbic acid occurs at about 0.3 V on the modified electrode while it occurs at 0.62 V on a bare glassy carbon electrode versus Ag/AgCl. The calibration graph from amperometric determination at applied potential of 0.35 V, shows a linear dependence between current and ascorbic acid concentration in the range of 5 x 10−6 M to 10−2 M R2 = 0.9999). The results of amperometric determination of ascorbic acid were compared with those obtained by the standard iodometric titration method and were found to be in good agreement. The loss in concentration of ascorbic acid under different storage conditions was studied. The concentration was determined amperometrically by standard addition method using the modified electrode. The degradation kinetics of ascorbic acid in orange juices during thermal treatment from 30-500C follows the first order kinetics. The value of the activation energy and Arrhenius constant were 3.39 KJ/mol and 0.96 min-1, respectively. From the analysis of the results, appropriate storage and transportation means of orange fruit was recommended.
