Heat treatment of curdlan enhances the enzymatic production of biologically active β-(1,3)-glucan oligosaccharides

• Laminaripentaose-producing enzyme (KfGH64) was expressed in Escherichia coli.
• Hydrolysis activity of KfGH64 toward intact curdlan was quite low.
• Pretreatment conditions of curdlan were evaluated to increase the hydrolysis rate.
• Heating at 90 °C for 30 min provided the best results.
• The hydrolysis rate was over 60% and the main product was laminaripentaose.

Biologically active β-(1,3)-glucan oligosaccharides were prepared from curdlan using GH64 enzyme (KfGH64). KfGH64 showed low activity toward native curdlan; thereby pretreatment conditions of curdlan were evaluated. KfGH64 showed the highest activity toward curdlan with heat treatment. The most efficient pretreatment (90 °C for 0.5 h) converted approximately 60% of curdlan into soluble saccharides under the optimized enzyme reaction conditions (pH 5.5, 37 °C, 100 rpm mixing speed, 24 h, and 10 μg of KfGH64/1 g of curdlan). The resulting products were predominantly laminaripentaose and a small amount of β-(1,3)-glucans with an average degree of polymerization (DP) of 13 and 130. The products did not contain small oligosaccharides (DP < 5), indicating that the hydrolysis of heat-treated curdlan by KfGH64 is a suitable method for the production of biologically active β-(1,3)-glucan oligosaccharides.