Ester Content and Jelly pH Influences on the Grade of Pectins

SUMMARY— A series of samples with percent esterification ranging from 73.7 to 28.6 was prepared under acid conditions at room temperature from lemon peel pectin that had been precipitated with aluminum. Molecular weight, as determined by viscosity in 1% Calgon, and galacturonic acid content remained unaltered during demethylation while equivalent weight decreased. Setting time increased until an ester content of around 50% was reached. At lower ester values setting time decreased again. Maximum jelly grades were obtained at an ester content of ca. 45%. However, at this ester level the pH at which a high jelly grade was obtained was very low and the grade decreased very rapidly as the jelly pH was increased to values above pH 2.2. The maximum grade obtained with a particular sample decreased and the pH at which this maximum grade could still be obtained increased as the ester content was increased above ca. 45%. Below this ester level, the maximum grade as well as the maximum pH at which this grade could be obtained decreased with ester content.