Development of a biotechnological process for the modification of galactomannan polymers with plant α-galactosidase

Abstract

Two galactomannan polysaccharides (guar gum, locust bean gum) are commonly used in foods and other applications to manipulate aqueous rheology. Locust bean gum (23% galactose, 77% mannose) is more functional and more expensive than guar gum (38% galactose, 62% mannose). We have investigated the enzymic (α-galactosidase) removal of side-chain galactose residues from guar gum to yield galactomannans similar in chemical composition and functional properties to locust bean gum. The optimum concentration for α-galactosidase action increased from ∼ 2% w/w (solution state) at 35°C to ∼ 10% w/w (gel-like state) at 42°C to 20–30% w/w (semi-solid particulate state) at 50°C due to increased enzymic temperature tolerance at high substrate concentrations. Galactomannans varying in galactose content were prepared by manipulating reaction time, temperature and enzyme/guar gum ratio. Enzymically modified guar galactomannans with 22–24% galactose contents were found to reproduce the rheological and stabilisation properties of locust bean gum. These findings form the basis for a feasible biotechnological route for the upgrading of guar gum to galactomannan polymers with enhanced functionality.