Microwave pretreatment of paramylon enhances the enzymatic production of soluble β-1,3-glucans with immunostimulatory activity

A hydrothermal microwave pretreatment was established to facilitate the enzymatic production of soluble bioactive beta-1,3-glucans from the recalcitrant substrate paramylon. The efficacy of this pretreatment was monitored with a newly developed direct Congo Red dye-based assay over a range of temperatures. Microwave pretreatment at 170 degrees C for 2 min resulted in a significantly enhanced enzymatic hydrolysis of paramylon. The action of endo-beta-1,3-and exo-beta-1,3-glucanases on the microwave-pretreated paramylon produced soluble beta-1,3-glucans with degrees of polymerisation (DP) ranging from 2-59 and 2-7, respectively. In comparison, acid-mediated hydrolysis of untreated paramylon resulted in beta-1,3-glucans with a DP range of 2-38. The hydrolysates were assayed on their immunostimulatory effect on murine macrophages by measuring the production of the inflammation-linked marker tumour necrosis factor alpha (TNF alpha) using immunofluorescence. All of the tested hydrolysis products were shown to induce TNF alpha production, with the most significant immunostimulatory effect observed with the hydrolysate from the exo-beta-1,3-glucanase treatment.