Optimization of pilot process for production of fermentable sugars and oligomers from grass fibre

In wales, an area of 1Mha representing 62% of agricultural land is utilised for growing perennial ryegrass. AberMagic is a perennial ryegrass that has been developed and exploited in grass biorefining at IBERS. The hemicellulose fraction presents in the grass fibre can be used for the production of high value products such as xylooligosaccharides and xylitol. To increase sugar release and thus the economics of an overall process, steam explosion (SE) followed by enzymatic digestion was used to develop a novel process for the production of xylooligosaccharides and xylitol from AberMagic grass Lolium perenne at pilot scale. A Taguchi Design of Experimental (DOE) concept (L₁₆ orthogonal array) was used to optimise the overall process.

Grass fibre having high amount of extractable sugars for fermentations and xylooligosaccharides production (1.1kg of extractable sugars: 0.7kg of Glucose, 0.3kg of Xylose and 0.1kg of Arabinose in 2kgs of fibre). At optimum condition the steam explosion pre-treatment released 20% of sugars in hydrolysate with a high concentration of xylose. Further hydrolysis of the pre-treated grass fibre with enzymes released 30% of the sugars with a high concentration of glucose.  The overall efficiency of the pre-treatment and hydrolysis was 50% as 0.5kg of the fermentable sugars released from 2kgs of grass fibre. Preliminary studies demonstrated that conversion of crude hydrolysate with high xylose to xylitol was achieved using Candida species. Further the xylose and xylooligosaccharides release from grass fibre was comparable with the sugars released from Miscanthus and wheat straw.