Temperature dependence of acid and calcium-induced low-methoxyl pectin gel extracted from Cyclea barbata Miers

The gel formation behaviour of green jelly leaf (GJL) pectins isolated by using water extraction method with extraction temperatures of 45, 65, 85 and 95 °C was investigated. The isolated pectins were also analysed for the yield, physicochemical and functional properties. The yield, molecular weight (M_w) and galacturonic acid content varied from ∼10 to 13% w/w, 3 × 10⁵ to 12 × 10⁵ g/mol and ∼75–86% w/w, respectively. Gelation of GJL pectins was a cold-setting gel and could be induced by acid and/or divalent ions; however, the latter gelation method showed a lesser temperature dependence than acid-induced gel. The addition of NaCl had enhanced the gel structure due to electrostatic screening effect. The mechanical spectra response showed that GJL pectin was typically gel-like with G′ greater than G″ and strongly influenced by pH and calcium concentration. The variation in pectin gel structures was also attributed to difference in pectin physicochemical properties particularly the degree of esterification (DE). Furthermore, lower DE pectins with higher charge values exhibited a stronger gel like properties with less variation on mechanical spectrum compared to higher DE pectins. These findings showed considerable potential of GJL pectin as a thickener and gelling agent and could be useful for development of low-sugar and high calcium content food with different textures.