The result was recorded as the initial titration volume once some pink color appeared. The number of
free carboxy group was calculated from the volume of 0.1 N sodium hydroxide solution spent for initial titration.
Then, 10 ml of 0.1 N sodium hydroxide was added to neutralize polygalacturonic acid. The sample was plugged
with a stopper and shaken vigorously, then allowed to stand at room temperature for 2 hours to de-esterify pectin. 10
ml of 0.1 N hydrochloric acid was added to neutralized sodium hydroxide and the sample was shaken until its pink
color disappeared. Three drops of phenolphthalein were added into the sample and the sample was further titrated
with 0.1 N sodium hydroxide. The volume of titration was recorded as final titration volume once some pink color
appeared. The number of the esterified carboxy group was calculated from the volume of 0.1 N sodium hydroxide
solution spent for final titration.