Preparation of a new chromogenic substrate to assay for β-galactanases that hydrolyse type II arabino-3,6-galactans

Abstract

A chromogenic assay using RB5-dGA, Reactive Black 5 (RB5) dye covalently coupled to de-arabinosylated gum arabic (dGA), was developed for rapid screening of β-galactanases. dGA was prepared by partial acid hydrolysis (0.25 M trifluoroacetic acid for 2 h at 90-95 °C) of gum Arabic (GA) from Acacia senegal. The dGA exhibited a median molecular mass of ∼10 kDa, corresponding to a degree of polymerisation (DP) ∼60. It was devoid of Ara residues, and contained mostly Galp (68 mol %) together with GlcpA (30 mol %). The Galp residues were (1,6)- (34 mol %), (1,3)- (3 mol %) and (1,3,6)- (26 mol %) linked, and the GlcAp residues were primarily terminal (28 mol %) together with a small amount of (1,4..