description
- Some fermentation processes, eg brewing, use cereal starch as their source of carbohydrate. Typically, the residue of the cereal grain is not separated until the end of the fermentation process. In distilleries or in processes designed to produce alcohol for fuel, the liquid stream then goes through distillation which leaves a liquid residue ("thin stillage"). In large scale operations, the liquid and grain residues are dried to produce "distillers dried grain and solubles" (DDGS) which can be used as animal feed. In the UK, at least 2 large-scale wheat to alcohol plants will soon be operating. These will convert low-grade feed-wheat (of which the UK typically has a surplus) to alcohol for use as an automotive fuel, co-producing large quantities of DDGS, of a fairly consistent composition. The industrial members of IBTI have set a challenge of adding value to this DDGS, which this project addresses. Apart from the starch, cereal grain is composed mainly of protein, fibre and other non-starch carbohydrate and fats. The main animal feed value is contained in the protein, but the high fibre content means that DDGS is only useful for ruminant animals. In this project we intend to separate some of the protein, carbohydrate and fats and use them to produce higher value products, while still retaining the option to use the protein component as an animal feed, possibly for poultry. The latter is important as using DDGS as animal feed replaces imported soybean and thus, can reduce the greenhouse gas (GHG) emissions associated with soybean production and importation. Therefore, the challenge breaks down into 2 parts: 1) devising methods to remove the non-starch carbohydrate and fat from the DDGS without destroying the feed value, and 2) finding ways to gain added value from the extracted components. For the first part we have assembled a multidisciplinary team who are experts in addressing the engineering, biological and animal nutrition components of this project. From a process engineering perspective it would actually make sense to use the separated distiller's grain, before addition of the "solubles", as our starting material. This would be difficult to obtain, so we will recover the grain component from the DDGS. Removal of the fats could be done with an organic solvent, but this might leave undesirable residues in the animal feed. As an alternative we will investigate the use of super-critical carbon dioxide (SCCO2) extraction; a gentle, residue free method used for making decaffeinated coffee. The fibre and other carbohydrates will be removed mainly with enzymes, but we will need to find gentle physical pre-treatments (hot water or a short steam treatment) to facilitate enzyme access to the carbohydrates. In (2), we will focus on upgrading the carbohydrate and protein components. The carbohydrate could be used in a second fermentation process, if an organism was available that could convert the carbohydrates to useful products. To reduce the cost of this process we would need to find/create an organism that could use most of the carbohydrate polymers directly, rather than adding separate enzymes, so this part of the programme will focus on identifying suitable enzymes and the genes that encode them to put into established process organisms. Producing additional fuel or other chemicals by a secondary fermentation will not only improve the economics but also the GHG balance of the process. The proteins contained in wheat grain are rather specialised in their make-up, having a high frequency of certain amino acids. Availability in large volumes offers a unique opportunity to make specific chemicals, and the feasibility of exploiting this renewable chemicals approach will comprise a second strand of activity. If successful, this will also have a GHG benefit. Together with projected uses of the fatty fraction we will combine data from the whole exercise into an economic model for independent evaluation by potential users.