Pectin from the fruit seeds of the creeping fig plant was extracted and its chemical composition and rheological properties determined. It was found to consist of ~87% galacturonic acid with a degree of methoxylation of ~20%. The polysaccharide produced a viscous solution at pH 4.5 and was shown to form strong gels when the pH was reduced by the addition of glucono-delta lactone. It was concluded that as the pH was lowered, the reduction in electrostatic repulsions between the pectin chains facilitated chain association mainly through hydrogen bonding. The rate of gelation increased considerably as the pH was reduced. Although the pectin was in the form of a solution at pH 4.5, the addition of Na+ and K+ salts resulted in gel formation. The strength of the gels was found to be dependent on both the concentration and nature of the added electrolyte in accordance with the Lyotropic series. It has been suggested that the role of the electrolyte was to reduce the electrostatic repulsions between the carboxylate groups along the pectin chains thus facilitating chain association. Association is promoted by the presence of a low concentration of Ca2+ ions (1.88% w/w) naturally present in the extracted material which facilitated the crosslinking of the pectin chains in addition to the association through hydrogen bonding
