Partial aqueous solubility of low-galactose-content galactomannans—What is the quantitative basis?

Galactomannans are nonionic, linear polysaccharides 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)-β-d-mannose) having degree of polymerization ∼1000, with a statistical distribution of single-unit (1 → 6)-α-d-galactose side groups. At low degrees of galactose substitution, these polymers are partially soluble in water and display a tendency to form mechanically weak gels in single-component solutions. Though partial solubility and gelation are linked to the concentration of galactose substituents and their substitutional pattern, a quantitative basis in terms of solvent quality and thermodynamic compatibility with other biopolymers has not been established. Here we summarize literature data relevant to the question of partial solubility in locust bean galactomannans. Based on our hypothesis that dissolution corresponds to an aqueous fractionation by composition and molecular weight, we suggest that water is a poor solvent for a significant portion of the polymeric components in this material. Further systematic studies of the solubility should offer new pathways to product enhancement by focusing on the underlying composition and molecular weight distributions.