Valorization of rice straw xylooligomers for biohydrogen production via cell-free synthetic enzymatic pathway

Abstract

Though first-generation biofuels threaten the world’s food supply, biomass-derived green hydrogen is becoming an alternative to conventional fuels. Rice straw (RS) is a non-edible and a good feedstock for producing hydrogen because it has significant levels of carbohydrates, which are easily converted into fermentable sugars. Xylooligomers (XOS) are the most prevalent oligomers in hemicellulose and can be obtained via the chemical and biological hydrolysis of xylan. In this study, XOS were prepared from rice straw xylan (RS-based xylan) using a modified acid hydrolysis process, and the produced XOS, specifically xylotriose (X3), was used for green hydrogen production using a cell-free synthetic enzymatic pathway (SythP) compared to commercial X3. This study reported the first-time green hydrogen production using XOS extracted from RS-based xylan. The results showed a great XOS production pattern from RS-based xylan upon addition of 5 µl of 4% sulfuric acid to 2% RS-based xylan, followed by autoclaving at 121 °C for 30 min. The synthesized XOS were used to generate hydrogen through water splitting at 50 °C via SythP. The hydrogen generation rates were 2.948 and 2.68 mmol/l, respectively, energized by commercial X3 and prepared X3, respectively. Accordingly, the hydrogen production rate utilizing the commercial one is slightly higher, which confirms that XOS made from RS-based xylan do not inhibit enzymes and efficiently produce hydrogen. Consequently, using lignocellulosic biomass to synthesize valuable XOS and their further application as an energy carrier is a promising sustainable approach for enzymatic green hydrogen production using the cell-free synthetic enzymatic pathway (SythP).