Equivalent weight is used to calculate the anhydrouronic acis content and the degree of esterification. It is determined by titration with sodium hydroxide to pH 7.5 using
either phenol indicator.0.5g of pectin substances (ammoniaand
ash-free) was weighed into a 250-ml conical flask. Then, it
was diluted with 5ml ethanol. 1g of sodium chloride was added
to sharpen the end point. 100ml of deionised water was added
together with six drops of phenol red or Hinton’s indicator. All
the pectin substances are made sure to have dissolved. Then, the
solution was titrated slowly with 0.1N NaOH until the colour of
the indicator changes (pH: 7.5). The neutralized solution was
used for methoxyl determination.