A characteristic of BIOCORE is the wide product portfolio that is being targeted, using a variety of technologies that employ novel tools, such as new enzymes and microbial strains or heterogeneous catalyst. Over the initial 24 months of the project several tools and processes have been investigated and, in certain cases, validated for pilot scale demonstrations.
Regarding enzymes, DSM has tested its proprietary thermostable cellulase cocktail on the C6 cellulose pulp produced by CIMV. Lab scale tests were highly successful, demonstrating that the performance of the enzymes is such that pilot scale trials are feasible. Likewise, DSM also screened its enzyme collection to identify enzymes that will be suitable for the depolymerization of xylo-oligomers contained within the C5-rich stream (a product of the CIMV process). Hemicellulase mixtures and single enzymes have now been identified, which might be useful for this purpose. Lab scale trials are currently on-going.
Work on microbial strains has forged ahead and highly promising results have been obtained by VTT. Working with yeast hosts, VTT has engineered new strains for the production of xylitol and xylonic acid, using xylose-rich syrups as the starting material. Currently the process performance of the best xylitol producing strain is at least equivalent or perhaps superior to that of any similar strain described so far in the literature. Therefore, these results are highly promising for future pilot scale trials.
The 5-carbon sugar d-xylose is a major component of the hemicelluloses-rich fraction arising from CIMV biomass refining. This naturally abundant sugar is useful, because it can be reduced to xylitol or oxidized to d-xylonic acid, compounds for which numerous applications exist.
Xylitol is well known as a sweetener in the agro-food industry. It procures a cool taste in the mouth and has been shown to have positive properties for dental health. Beyond the agro-food sector, xylitol has been identified as a promising platform chemical for the synthesis of polymers. Currently, xylitol is manufactured via a chemical process, but it can also be produced thanks to the action of xylose reductase. Potentially, the biocatalytic production of xylitol could offer both economic and environmental benefits, especially if a highly specific process producing high quality xylitol from complex biomass hydrolysates could be developed. Nevertheless, to be economically viable, it is necessary to develop a robust microbial strain that can produce xylitol in high yields and at high productivity. In the BIOCORE project, researchers from VTT are tackling this challenge and are aiming to demonstrate a biotechnological process at pilot scale within the lifetime of the project. In the initial phase of this work, VTT scientists have prepared several engineered yeast strains, using a variety of xylose reductases. Currently, the best performing strain can produce over 100 g xylitol l-1 at high productivity.
Regarding d-xylonic acid, it has been demonstrated that this chemical can be used as a dispersant in cement applications, as a chelating agent, as a precursor for the energetic compound 1,2,4-butanetriol and could be useful as building block for the synthesis of hydrogels. Previous work has shown that Pseudomonas and Gluconobacter species can produce xylonic acid from pure D-xylose, though commercial bulk scale production has not been developed. This is because the production of xylonic acid from lignocellulosic hydrolysates is a prerequisite for economic viability. Unfortunately, the previously cited strains are intolerant to the inhibitors present in such hydrolysates. Therefore, in the BIOCORE project, researchers from VTT are aiming to combine the properties of robust yeast strains, tolerant to lignocellulosic hydrolysates, with the ability to synthesize d-xylonic acid (or its conjugate base d-xylonate) at high yield and high productivity. Thus far, yeast strains have been constructed and improvements to these have been made. The best strain at this stage in the project is able to produce up 90 g.L-1 of xylonate using pure xylose as starting material.