33A-22 |
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S.-H. YOO, Department of Food Sicence and Technology, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul, 143-747, South Korea, M. L. Fishman, Eastern Regional Research Center, U.S. Department of Agriculture, and H. G. Lee, Department of Food and Nutrition, Hanyang University, South Korea. In the presence of 0.2M monovalent salts, pectin gels were induced by the action of pectin methylesterase (PME) at constant pHs. Without salt or PME, the pectin gelation did not occur. The gelling ability and gel strength were influenced by both pH and species of monovalent cation. At pH 5.0, the KCl-induced pectin gel was substantially stronger than the NaCl-induced gel. However, NaCl made a much stronger gel at pH 7.0. LiCl did not form gel structure at either pH. In syneresis tests, KCl-induced gels were more stable (less water loss) than NaCl-induced gels at both pHs. Molecular weights (Mw) of pectins, by using high-performance size-exclusion chromatography (HPSEC) with on-line multi-angle laser-light scattering (MALLS) detector, increased from 1.38 * 105 to 2.26 * 105 during PME-driven NaCl-induced gelation at pH 7. The increase in Mw can be explained by a hypothetical PME-transacylating activity. Alternatively, the Mw increase may be attributed to the aggregation of enzymatically-deesterified low-methoxy pectin. To present a possible explanation, we determined the effect of monovalent salts on the hydrodynamic property of pectin solutions. Simple automated capillary viscometric analysis revealed that low-methoxy (LM) pectin consistently had larger reduced viscosity (hred) than high-methoxy (HM) pectin regardless of salt concentration. The hreds of HM-pectin were fairly constant, whereas the hreds of LM-pectin had a tendency to decrease as the pectin concentration approached to zero. The effect of salt type on the pectin behavior in both LM- and HM-pectin solutions was marginal, whereas the level of salts in the pectin solution drastically affected intrinsic viscosity ([h]) of LM-pectin, whereas the [h] of HM-pectin was relatively constant. Therefore, the structural differences represented by different level of methyl esters are mainly responsible for the distinct solution behaviors of LM- and HM-pectins.
Session 33A, Carbohydrate: General
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