Maximising bioethanol processing yield of UK wheat: effects of non starch polysaccharides in grain

Abstract

The objectives of the project were to understand differences in alcohol yield (AY) between UK wheats typical of those which would be delivered to a biofuel distillery including hard endosperm and 1B1R wheats (i.e. those containing the 1BL/1RS translocation), to quantify the importance of non starch polysaccharides (NSP) in wheat grain with respect to variation in AY, and to use this information to guide plant breeders, growers, distillers and operators of UK bioethanol plants.barley malt as a source of enzymes and free amino N) was transferred to the ADAS lab, and later adapted to an enzyme-only method, representative of a biofuel distillery. The modified enzyme method was used to screen a set of samples from a variety x N response experiment harvested at ADAS High Mowthorpe, comparing two varieties Ambrosia (+1B1R) and Istabraq (-1B1R) with 6 levels of fertilizer N from 0 to 340 kg/ha and the NSP contents measured. Fermented and distilled samples were also assessed for their residue viscosity (RV) which gives an indication of processing quality. A set of 30 commercial samples at a fixed protein content of 11.5% was also selected from a larger dataset, to provide representation of the major nabim wheat classes, and their AY, RV and NSP contents determined. There was a significant negative relationship between AY and grain protein, but no significant effects of fertiliser N on NSP concentration, and no significant difference in average AY or NSP between Ambrosia and Istabraq. However, it was noted that Ambrosia is not entirely typical of the 1B1R wheats which have historically given processing problems, hence other 1B1R wheats may have higher NSP levels. Interestingly, RV increased significantly with increasing grain protein content (in response to fertiliser N) indicating that soluble proteins, rather than arabinoxylans, may be responsible for differences in poor processing quality in high protein wheats. For wheat samples studied at a fixed protein content, there was a negative relationship between average AY and NSP content when wheats were arranged by nabim classification, with Groups 3 and 4 soft wheats having the highest AY and lowest NSP levels. Group 1 wheats had the highest NSP contents. On average reduction of 2 g/100g in NSP content gave an increase in AY of 14 L/t at a fixed protein content. The analysis suggests that in order to fully understand variation in AY in wheat grain, more information is needed on the other non-starch, non-protein fractions such as oil and ash, and also data quantifying the rate and extent of starch digestibility.