Reducing Arabitol Formation to Improve Xylitol Production from Brewers Spent Grains an exemplar process

Globally, the top 25 beer producing nations manufacture 186 billion litres/year1, with low to middle income countries (LMICs) manufacturing »50% of the world’s beer supply generating 313 million tons (mt) dry weight (DW) of brewers spent grains. Currently, the UK produces >7.3 mt BSG DW. Used as a low-value (£35-48/t) animal feed2, BSG is a rich source of xylose (»16% DW) that could be extracted and processed to xylitol (£2.5-£3.5k/t) with the majority of the fibrous residue returning back into the food chain. However, the relatively high levels of arabinose (»11% DW) prevent valorisation and route to a market that is expected to be $1bn by 20203. IBERS have developed a rapidly fermenting yeast strain using GM and other strategies that maximises xylitol production achieving 100% conversion from unrefined, lignocellulosic xylose. Working with SA Brain & Company, the largest brewery in Wales, we will adopt a synthetic biology and adaptation approach to prevent arabitol accumulation and increase productivity in BSG fermentations: 1) using IBERS established genetic tools and resources, we will abolish arabitol production in our improved, proprietary C5 utilising yeast by diverting arabinose into biomass to further accelerate yeast growth and xylitol productivity4 and 2) improve this arabitol negative C5 yeast strain through successive rounds of adaptation and fermentation in BSG hydrolysates. PoC objectives: 1) Produce xylitol accumulating yeast capable of efficiently fermenting BSG hydrolysates without producing arabitol; 2) Optimise BSG hydrolysate fermentation to xylitol; 3) Estimate the technoeconomic impact of scaling the technology through to commercialisation.