ARABINOXYLAN PREBIOTICS CO-PRODUCTION WITHIN INTEGRATED BIOREFINERIES

In cereal-based biorefineries, Distillers Dried Grains with Solubles (DDGS) is the main by-product, which is used in relatively low value animal feed formulations. A major component of DDGS is arabinoxylan (AX), which is a potential food ingredient and source of novel prebiotics. The production of AX uses large amounts of ethanol, which gives scope for feasible integration of AX extraction within a biorefinery. Meanwhile, enzymatic production of prebiotic arabinoxylan oligosaccharides (AXOS) and xylo-oligosaccharides (XOS) is of interest to animal feed formulators, as these prebiotics enhance feed conversion significantly.

The integration scenario would be implemented on the in-process streams, the Distillers Wet Grain (DWG) and the Solubles before they are combined. However, these are not readily available to study, as biorefineries are closed processes that do not allow in-process sampling of these streams. Therefore, this project used the GUNTCE-640 bioethanol unit to produce wet by-products representative of commercial DWG. Fermentation often batches of 6kg of wheat yielded on average 1275g (db) of DWG with 16% AX content and 800g of dry Solubles with 11.4% AX content.

Enzymatic treatment of the DWG with commercial endoxylanase yielded less than 3%w/w of the prebiotic oligosaccharides. AX polysaccharides were extracted by alkaline oxidation, with and without further enzymatic purification, to give AX contents of 44% and 19%, respectively. Enzymatic treatment converted only 6% of the AX into AXOS/XOS, with significant production of undesired monosaccharides.

Limitations in the analytical methods used prompted the development of a new HPAEC-PAD method for the simultaneous measurement of mono-and oligosaccharides and uronic acids. The new method was used to quantify the profiles of XOSin commercial materials and following enzyme treatment of biomass materials and oligosaccharide standards up to DP6, the latter to reveal the xylanase mode of action. The commercial xylanase investigated showed a preference for larger XOS molecules and was incapable of acting on branched (AXOS) molecules.

Two types of AX with different branching patterns were produced; highly branched AX was extracted chemically from DWG with further purification to give 51% w/w purity, and less branched AX was produced from the Solubles fraction by ultrafiltration to give 74% purity. Enzyme treatment converted 46% of the Solubles AX into oligosaccharides, showing this to be a promising feedstock for XOS production.