Physicochemical properties of pectins from okra (Abelmoschus esculentus (L.) Moench) |
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Authors: | Nipaporn Sengkhamparn Leonard MC Sagis Renko de Vries Henk A Schols Tanaboon Sajjaanantakul Alphons GJ Voragen |
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Affiliation: | 1. Laboratory of Food Chemistry, Department of Agrotechnology and Food Sciences, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands;2. Department of Food Science and Technology, Faculty of Agro-Industry, Kasetsart University, Ladyao, Jatujak, Bangkok 10900, Thailand;3. Food Physics Group, Department of Agrotechnology and Food Sciences, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands;4. Laboratory of Physical Chemistry and Colloid Science, Wageningen University, P.O.Box 8038, 6700 EK Wageningen, The Netherlands |
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Abstract: | Okra pectin obtained by hot buffer extraction (HBSS) consists of an unusual pectic rhamnogalacturonan I structure in which acetyl groups and alpha galactose residues are substituted on rhamnose residues within the backbone. The okra Chelating agent Soluble Solids (CHSS) pectin consists of slightly different structures since relatively more homogalacturonan is present within the macromolecule and the rhamnogalacturonan I segments carry slightly longer side chains. The rheological properties of both okra pectins were examined under various conditions in order to understand the unusual slimy behaviour of okra pectins. The viscosity of the okra HBSS pectin was 5–8 times higher than the viscosity of the okra CHSS pectin. The okra HBSS pectin showed an elastic behaviour (G′ > G″) over a wide range of frequencies (10−1–10 Hz), at a strain of 10%, while okra CHSS and saponified okra HBSS/CHSS pectin showed predominantly viscous responses (G′ < G″) over the same frequency range. The results suggest that the structural variation within the okra pectins greatly affect their rheological behaviour and it is suggested that acetylation of the pectin plays an important role through hydrophobic associations. Dynamic light scattering was used to study the association behaviour of both okra pectins at low concentration (0.001–0.1% w/w). Results showed that the saponified okra pectins did not exhibit a tendency to aggregate in the concentration range studied, whereas both non saponified samples showed a substantial degree of association. These results suggest that the unusual slimy behaviour of the non saponified samples may be related to the tendency of these pectins to associate, driven by hydrophobic interactions. |
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Keywords: | Okra Pectin Rhamnogalacturonan I Rheological properties Dynamic light scattering Hydrophobic association |
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