ALACEN: A Holistic Herbaceous Biomass Fractionation Process Attaining a Xylose-Rich Stream for Direct Microbial Conversion to Bioplastics

Lignocellulose biorefining is a promising technology for the sustainable production of chemicals and biopolymers. Usually, when one component is focused on, the chemical nature and yield of the others are compromised. Thus, one of the bottlenecks in biomass biorefining is harnessing the maximum value from all of the lignocellulosic components. Here, we describe a mild stepwise process in a flow-through setup leading to separate flow-out streams containing cinnamic acid derivatives, glucose, xylose, and lignin as the main components from different herbaceous sources. The proposed process shows that minimal degradation of the individual components and conservation of their natural structure are possible. Under optimized conditions, the following fractions are produced from wheat straw based on their respective contents in the feed by the ALkaline ACid ENzyme process: (i) 78% ferulic acid from a mild ALkali step, (ii) 51% monomeric xylose free of fermentation inhibitors by mild ACidic treatment, (iii) 82% glucose from ENzymatic degradation of cellulose, and (iv) 55% native-like lignin. The benefits of using the flow-through setup are demonstrated. The retention of the lignin aryl ether structure was confirmed by HSQC NMR, and this allowed monomers to form from hydrogenolysis. More importantly, the crude xylose-rich fraction was shown to be suitable for producing polyhydroxybutyrate bioplastics. The direct use of the xylose-rich fraction by means of the thermophilic bacteria Schlegelella thermodepolymerans matched 91% of the PHA produced with commercial pure xylose, achieving 138.6 mgPHA/gxylose. Overall, the ALACEN fractionation method allows for a holistic valorization of the principal components of herbaceous biomasses.


List of tables
Table S1: Total quantity (g) of each component during the ALACEN fractionation steps ................... S14 Table S2 Comparison of water acid and base usage of a current commercial xylose production plant (Pang et al., 2021)           A) the NREL protocol was performed after each stage of the ALACEN process, b) NREL was performed only for the initial biomass and the residue after the ALACEN process, for the rest of the stages acid hydrolysis with 4%w/w H2SO4 at 120°C was performed on the supernatant, and therefore the lignin content is missing in the mild alkaline (AH) and diluted acid (DA) treatments, indicated by -

Figure S2GC -
Figure S2GC-FID chromatogram of the liquid fraction obtained after catalytic hydrogenolysis of the lignin

Figure S4 :
Figure S4: lignocellulose composition of wheat straw (initial) and dilute acid pretreated wheat straw

Figure S6 :
Figure S6: 1H NMR analysis of the bioplastics produced by S. thermodepolymerans with the diluted acid

Figure S7 :
Figure S7: Thermal gravimetric analysis (TGA) analysis of the bioplastics produced by S.

Figure S8 :
Figure S8: Differential scanning calorimetry (DSC) analysis of the bioplastics produced by S.

Figure S9 :
Figure S9: Representation of the consumption over time of the total xylose (left) and PHB production

Figure S10 :
Figure S10: Gel permeation chromatography of the evolution of the direct diluted acid sample (green

Figure S11 :
Figure S11: Yield and identification of the monomeric phenolics obtained after the REL and ALACEN

Table S1 :
Total quantity (g) of each component during the ALACEN fractionation steps

Table S2
Comparison of water acid and base usage of a current commercial xylose production plant 1 and the ALACEN process.