Abstract
The molecular characteristics, dynamic viscoelasticity in the gelation process and gel of variously demethylated low methoxyl pectin are examined. The following results are obtained :
1) Methoxyl contents of ammonia-demethylated (ALM) pectin, enzyme-demethylated (ELM) pectin, and acid-demethylated (CLM) pectin were found almost the same. Their molecular weights, and molecular sizes determined by light scattering method were (2.23.6) × 105, and 650780Å, respectively.
3) The analyses of functional groups in variously demethylated pectin were performed by infrared spectroscopy using KBr-tablet method.
3) The storage modulus (E′) and loss modulus (E″) observed during gelation process of 1% pectin sol in the presence of Ca2+ were measured with Rheolograph PV-100. The order of the respective values of these three pectins were as follows :
E′ : ALM> ELM> CLM pectin, E″ : ALM> CLM> ELM pectin.
The mechanical loss tangent (E″/E′) value of CLM pectin was greater than those of other two types of pectin.
4) The dynamic viscoelasticity measured with Rheolograph CV-100 of 2% pectin gel was large in the order of ALM> ELM> CLM pectin. The pH dependence was large in the order of ALM> CLM> ELM pectin, showing that the molecular weight, molecular size, and types and contents of functional groups of pectin correspond sharply to changes in pH values.
