Spectrophotometric quantification of ascorbic acid contents of fruit and vegetables using the 2,4-dinitrophenylhydrazine method

Accurate quantification of the nutritional and antioxidant properties of raw materials is important in the diet and nutritional management. In this study, the 2,4-dinitrophenylhydrazine colorimetric method widely used for determination of ascorbic acid level in biological fluids was adapted to estimate total vitamin C content in fruits. The procedure depends on the principle of oxidation of L-ascorbic acid to dehydroascorbic acid and 2,3diketo-gulonic acid, followed by reaction with 2,4-dinitrophenylhydrazine. After treatment with sulfuric acid, a colored product is formed which is absorbed at 520 nm. Using standard ascorbic acid at different concentrations, Beer’s law was obeyed up to 2.0 mg dL -1 concentration range, which resulted in the following equation of the linear calibration curve: y = 4.0827x - 0.0423, R 2 = 0.9923. The most critical and decisive step in the procedure for an accurate reading is the preparation of a final clear extract of the fruit or vegetable. Analysis of vitamin C contents in selected fruit using both titrimetric and spectrophotometric methods are presented.