Influence of pH, pectin and Ca concentration on gelation properties of low-methoxyl pectin extracted from Cyclea barbata Miers

Pectin isolated from Cyclea barbata Miers leaf (green jelly leaf) forms a gel at a low pH (∼≤3) in the absence of co-solutes and divalent ions at room temperature. These gelling properties are important and particularly useful in the development of low-sugar food systems. In this study, rheological measurements were employed to determine the effect of varying different levels of pH, pectin, urea and divalent ions (Ca²⁺) concentration towards the gelation properties of the isolated pectin. The gelation time and gel physical properties were investigated by determining the gel-sol transition time and the mechanical spectra (G’ and G”) using oscillatory measurements. This study showed that acid-induced gelation of the extracted pectin was mediated by hydrogen bonding and gelation only occurred at pH ≤3. The results obtained from oscillatory measurements showed that gel strength of green jelly leaf (GJL) pectin was affected by varying pectin concentration where gel strength increased with increasing pectin concentration. However, when compared with a pectin with a lesser charge density (Genu pectin, DE 31%), the gel strength of GJL pectin at different concentrations were lower. Presumably the abrupt formation (due to highly negative charge) of cross-linking junction of GJL pectin molecules had led to un-homogenous gel network and resulting in weaker gels.