Vitamin C determination
The vitamin C content in the sample was determined by spectrophotometric method as described by AOAC (2005) and Rahman et al., (2007) using 2, 4-dinitrophenylhydrazine. 10 g of the potato tubers was homogenized with 50 ml of distilled water. 2 ml of each sample homogenate was pipetted into test tubes; 38 ml of 0.5% oxalic acid was added, mixed and incubated at 50oC for an hour. The tubes were transferred to an ice-water bath for 5 min, 2.5 ml of 85% H2SO4 was added to the tubes in the ice-water bath drop-wise with mixing after each drop. The test tubes were removed from the ice-bath and left to cool at room temperature for 30 min. The absorbance was measured at 520 nm against the blank (2 ml of 4% TCA with 1 ml of 2,4-dinitrophenylhydrazine).
Concentration of Vitamin C (mg/100ml) =
Absorbance of sample × concentration of standard / Absorbance of standard