Chemical modification of citrus pectin to improve its dissolution into water

Citrus pectin was modified with glycine, glycine methyl ester, or glycylglycine by the use of intramolecular associations in polar organic solvents. The modified pectins except glycine methyl ester significantly improved its dissolution in water, compared with unmodified pectin. The pectin modified with glycylglycine was the most soluble into water and was not influenced by pH range from 4.6 to 7.6 and ionic strength range from 1 mM to 50 mM phosphate buffer (pH 5.1), while the dissolution of the unmodified pectin decreased as pH and ionic strength increased. The required time at 45 °C at 95% hydration rate in the glycylglycine-modified pectin (2%, w/v) was toward 58% that in the unmodified pectin. In glycylglycine-modified pectin, the hydration rate was dependent on the bound amounts of the modifying agent to pectin. The potentiometric titration curves revealed that the glycylglycine-modified pectin would bear more negative charge than the unmodified pectin. From analysis of the water adsorption isotherms, the Brunauer–Emmett–Teller C constant as an index of hydrophilicity in the glycylglycine-modified pectin was 1.23-fold and 1.87-fold, respectively, higher than those in the unmodified and glycine methyl ester-modified pectins. These results suggested that the dissolution of pectin into water was preferably related to the net charge and the surface hydrophilicity in pectin molecules.