Dr. Oni Yuliarti
FSI-Food Technology, Massey University, School of Chemical and Life Sciences, Singapore Polytechnic
Street : 500 Dover Road, Clementi Singapore 139651
A Novel Pectin from Green Jelly leaf (Cyclea barbata Miers): Rheological properties of the fresh water extract gel.
The water extract of green jelly leaf (Cyclea barbata Miers) formed gels when the leaves were disintegrated with water at room temperature without additional ingredients. The water extract polysaccharide fraction was found to contain mainly galacturonic acid (~35.8% w/w) and neutral sugars (6.8% w/w) such as rhamnose (~0.2% w/w), arabinose (0.5% w/w), galactose (~2.6 % w/w), mannose (~2.8% w/w), glucose (~0.5% w/w), xylose (~0.10% w/w) and fucose (~0.10% w/w). The polysaccharide fraction has an average weight molecular weight of ~4.4×105 g/mol. Analysis obtained from Fourier transformed infrared spectroscopy (FTIR) showed that extract has a similar FTIR fingerprint as a commercial low methoxyl pectin (LMP, 31% DE). However, in the case of the polysaccharide from the extract, there was a complete absence of methyl esterified carbonyl group indicating zero degree of esterification. This study has shown that the ability of the leaves to perform spontaneous gel was due to the large amount of highly negatively charged pectic polysaccharide present (-74.1 mV) that is sensitive to the divalent ions content (~1.5% w/w, mostly in the form of calcium) of the leaves. The rheological properties of fresh water extract (1% w/w) showed that there was no definite gelation temperature as the gelation time could occur at any temperatures (i.e. 20, 60 and 80°C) as indicated by the crossover of G’ (storage modulus) above G” (loss modulus). The study showed that the gelation was cation-mediated and could be potentially used as a novel polysaccharide which offers a unique functional gelling system.
Keywords: Water extract; galacturonic acid; low methoxyl pectin; gelation.