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CPP: Chemische Physik und Polymerphysik

CPP 9: SYMPOSIUM Disperse Polymer Systems II

CPP 9.7: Vortrag

Dienstag, 28. März 2006, 16:15–16:30, ZEU 160

What is the link between gelation and partial solubility in the galactomannan polysaccharides? — •Michael Pollard and Peter Fischer — Laboratory for Food Process Engineering, Swiss Federal Institute of Technology, Zürich CH-8006

We are interested in the structure-property relations of the galactomannan storage polysaccharides found in the endosperm of Legumes. These nonionic, linear polysaccharides are used as thickeners/stabilizers, co-gellants, and fat replacers in ice creams, sauces, and other food products. The primary biosynthetic product is a poly((1-4)-beta-D-mannose) having degree of polymerization ~1000, with a statistical distribution of single-unit (1-6)-alpha-D-galactose side groups. These side-groups confer aqueous solubility via H-bonding at degrees of substitution greater than 20%; linear mannans are otherwise water-insoluble No-dqcellulosicNo-dq polymers.

Locust Bean (Ceratonia siliqua) galactomannans display temperature-dependent aqueous solubility and a tendency to form weak gels without co-gellants present. Both properties are exploited to provide triggered viscosity increases and enhanced gel properties in ready-mix and frozen products, but the physical basis is poorly understood. The low galactose content and apparent statistical-blocky character of their distribution both probably play a role in the dissolution and gelation properties, but quantitative links have been very difficult to establish. We argue here that dissolving LB galactomannans effectively fractionates by chemical composition and possibly chain length, implying that the gels observed upon cooling may be a manifestation of very slow L-L demixing.