Feasibility of co-producing arabinoxylans and ethanol in a wheat biorefinery: Fractionation studies on UK wheats

Abstract

Arabinoxylans (AX) are a promising candidate for co-production alongside bioethanol in an integrated wheat biorefinery, having both food and pharmaceutical uses. However, the economics of a biorefinery depend strongly on wheat composition.

Ten wheat varieties, representative of the range of compositional variation in UK wheats, were analysed for grain size and shape, protein, starch and arabinoxylan contents, in order to assess effects on biorefinery economics. The wheats were also fractionated by pearling and milling to produce a total of 100 different milling fractions, and the arabinoxylan, protein and ash contents quantified in order to identify suitable fractions for AX extraction. Following debranning, the 4% pearlings fraction (dominated by the outer bran layers) was found to have higher arabinoxylan contents than other fractions. In contrast, protein, which acts as a contaminant in AX production, was concentrated in the inner bran layers.

Economic simulations based on arabinoxylan extraction from the 4% pearlings showed the effects of starch and arabinoxylan contents on ethanol and AX costs, respectively, and identified the most promising wheats for processing into bioethanol and AX. Some wheats were suitable for both AX and bioethanol production, whereas some were suitable for neither. Actual measurements of alcohol yield of selected grain and flour samples indicated that bioethanol yield could not be predicted from starch content alone, as the two good distilling wheats had higher alcohol yields than would be predicted by their starch contents alone.