The gene encoding an alpha-galactosidase from guar seed has been isolated and identified. It has been expressed in yeasts, e.g. Saccharomyces, Kluyveromyces and Hansenula, in bacteria, e.g. Bacillus, and in plants, e.g. Nicotiana. The resulting alpha-galactosidase is able to decrease the galactose content of galactomannans such a guar gum by splitting off 1-6 linked alpha-D-galactopyranosyl units attached to a main chain of 1-4 lined beta-mannopyranosyl units. Thus a commercially feasible process becomes available for producing alpha-galactosidases suitable for providing galactomannans having improved properties, which can meet the increasing demand for good quality polysaccharides. It has further been demonstrated that other alphagalactosidases, which show a positive immunological cross-reaction with an antibody raised against the alpha-galactosidase from guar, are also effective in decreasing the galactose content of galactomannans such as guar.