Approach towards biocatalytic valorisation of barley β-glucan for bioethanol production using 1,3-1,4 β-glucanase and thermotolerant yeast

The exploitation of renewable resource containing polymers other than cellulose and hemicellulose are critically important for the feasibility of biofuel production. The potential of 1,3-1,4 glucan 4-gluconohydrolyase mediated saccharification of barley β-glucan (BG) was investigated for ethanol production using thermotolerant Saccharomyces sp. A maximum hydrolysis of 71% was obtained in 24 h using in-house produced 1,3-1,4 β-glucanase from an alkalothermophilic Thermomonospora sp. whereas the hydrolysis was 100% with Accellerase™ 1000. The synergistic effect of β-glucosidase and 1,3-1,4 β-glucanase was demonstrated by the exogenous addition of β-glucosidase to Thermomonospora 1,3-1,4 β-glucanase which resulted in complete hydrolysis of BG. The hydrolysates of BG obtained using Accellerase or a cocktail of Thermomonospora 1,3-1,4 β-glucanase and β-glucosidase when fermented with free cells of Saccharomyces at 40 °C produced an ethanol yield of 0.44 g g−1 and 0.46 g g−1 respectively and when fermented with immobilized cells produced a yield of 0.49 g g−1. The Ca-alginate immobilized yeast cells were reused nine times at 40 °C with 100% fermentation efficiency. The economics of barley-to-fuel ethanol program will ameliorate if in addition to barley starch, β-glucan is also utilized.

► Exploitation of alternative renewable resources for the feasibility of biofuel production.
► 1,3-1,4-β-glucanase mediated hydrolysis of barley β-glucan.
► Synergistic effect of β-glucosidase and β-glucanase in the hydrolysis of β-glucan.
► Ethanol production from hydrolysates using thermotolerant Saccharomyces at 40 °C.