The modes of action of three thermostable 1,3(4)-beta-D-glucanases (EG V-VII) purified from the fungus Talaromyces emersonii were investigated on a pure commercial (1,3)(1,4)-beta-D-glucan and on a crude beta-glucan preparation isolated from barley mash to evaluate their potential for application in brewing, animal feed and human foodstuffs industries. Depolymerizing capability was evaluated by monitoring changes in viscosity of 10 mg ml(-1) solutions of each substrate over a 10 min (600 s) reaction period, by estimating %hydrolysis over a 24 h incubation period at 50 degrees C and quantifying oligosaccharide products of hydrolysis formed using high-performance anion-exchange chromatography (HPAEC). The results demonstrated that all three enzymes were markedly more active on the crude beta-glucan, which was evident in more extensive viscosity changes and higher %hydrolysis values. Distinct differences were observed in the profiles of products released from both beta-glucans by EG V-VII. The results indicate the potential of the enzymes for target applications, and also demonstrate the need to evaluate enzyme potential using native substrates. (c) 2004 Elsevier Ltd. All rights reserved.