Efficient Enzymatic Hydrolysis of Biomass Hemicellulose in the Absence of Bulk Water.

Current enzymatic methods for hemicellulosic biomass depolymerization are solution-based, typically require a harsh chemical pre-treatment of the material and large volumes of water, yet lack in efficiency. In our study, xylanase (E.C. 3.2.1.8) from Thermomyces lanuginosus is used to hydrolyze xylans from different sources. We report an innovative enzymatic process which avoids the use of bulk aqueous, organic or inorganic solvent, and enables hydrolysis of hemicellulose directly from chemically untreated biomass, to low-weight, soluble oligoxylosaccharides in >70% yields.

Sustainable PHA production in integrated lignocellulose biorefineries.

In emerging bioeconomies, the compostable biopolymers polyhydroxyalkanoates (PHAs) are desirable products due to their similarity to petropolymers. While industrial PHA production has been growing rapidly, obtaining a cheap and sustainable carbon source is still a challenge. Among biobased feedstocks, lignocellulose is a cheap, abundant and potentially sustainable carbon source. However, because of its recalcitrance, separation and depolymerization processes that have not reached industrial maturity are usually required. Integrated biorefineries utilize a holistic approach to conversion processes to minimize feedstock price and maximize resource use. This review examines the technical feasibility of merging PHA production and lignocellulose biorefining in integrated processing facilities. Among lignocellulosic feedstocks, wood is a promising carbon source due to its mature industrial infrastructure. Among the lignocellulose components, the hemicellulose fraction is the most promising feedstock for PHA production since it is underutilized and can be combined with bioethanol production from the cellulose fraction. Fractionation processes allow separate recovery of cellulose, hemicellulose and lignin, to which PHA can be added as a co-product.

Model Study To Assess Softwood Hemicellulose Hydrolysates as the Carbon Source for PHB Production in Paraburkholderia sacchari IPT 101.

Softwood hemicellulose hydrolysates are a cheap source of sugars that can be used as a feedstock to produce polyhydroxybutyrates (PHB), which are biobased and compostable bacterial polyesters. To assess the potential of the hemicellulosic sugars as a carbon source for PHB production, synthetic media containing softwood hemicellulose sugars (glucose, mannose, galactose, xylose, arabinose) and the potentially inhibitory lignocellulose degradation products (acetic acid, 5-hydroxymethylfurfural (HMF), furfural, and vanillin) were fermented with the model strain Paraburkholderia sacchari IPT 101. Relative to pure glucose, individual fermentation for 24 h with 20 g/L mannose or galactose exhibited maximum specific growth rates of 97% and 60%, respectively. On the other hand, with sugar mixtures of glucose, mannose, galactose, xylose, and arabinose, the strain converted all sugars simultaneously to reach a maximum PHB concentration of 5.72 g/L and 80.5% PHB after 51 h. The addition of the inhibitor mixture at the following concentration, sodium acetate (2.11 g/L), HMF (0.67 g/L), furfural (0.66 g/L), and vanillin (0.93 g/L), to the sugar mixture stopped the growth entirely within 24 h. Individually, the inhibitors either had no effect or only reduced growth. Moreover, it was found that a bacterial inoculum with high initial cell density (optical density, OD ≥ 5.6) could overcome the growth inhibition to yield an OD of 13 within 24 h. Therefore, softwood hemicellulose sugars are viable carbon sources for PHB production. Nevertheless, real softwood hemicellulose hydrolysates need detoxification or a high inoculum to overcome inhibitory effects and allow bacterial growth.