2.7.4. Determination of Degree of Esterification

The degree of esterification (DE) of extracted pectin was calculated by means of the titration method [17] with slight modifications, as described by Hosseini et al. [18]. Dried pectin (0.1 g) was wetted with 2 mL ethanol. Distilled water at 40 °C (20 mL) was added and kept under stirring. After complete dissolution of the sample, 5 drops of phenolphthalein were added, and the solution was titrated with 0.1 M NaOH (V₁). Then, 10 mL of 0.5 M NaOH was added. The sample was left to stand for 20 min for hydrolysis. Following, 10 mL of 0.5 HCl was added under stirring till the pink color disappeared. At the end, 5 drops of phenolphthalein were added, and the titration occurred through the addition of 0.1 M NaOH until a slight pink color persisted (V₂). DE of the pectin was calculated according the following equation (Equation (1)):

Commercial pectin (Sigma-Aldrich P9135) was analyzed for comparison.