Fractionation and exploitation of the component value of DDGS

Lead Research Organisation: University of Bath
Department Name: Biology and Biochemistry

Abstract

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.

Technical Summary

The large scale availability of DDGS from UK feed-wheat based bioethanol plants provides an opportunity to consider enhancing its value. DDGS is made by separating the residue of the wheat grain, post-fermentation (distillers grain) with a "solubles" syrup created by concentration of the "thin stillage" recovered post-distillation. We argue that the best place to add value is to extract material at the distillers grain stage. Furthermore, we maintain that extraction should be gentle enough to maintain the animal feed value of the protein in the residue, once combined with the "solubles". For reasons of practicality we will initially use a surrogate "distillers grain" by recovering the solids from DDGS, but through collaborations with Vivergo, may be able to access the real product as the project progresses.
The ultimate aim is to extract fat/oil using supercritical CO2, use the distillers grain in a second fermentation by hydrolysis and microbial metabolism of the non-starch carbohydrates and use some of the protein in biocatalytic upgrading to defined chemical products. In the first stage of the project, where we will be developing methods to extract fat/oil, release and hydrolyse the carbohydrate and selectively metabolise certain protein components, we will benchmark the suitability of the methods by the level of retention of the animal feed value of the residue. Not only do we intend to retain the feed value, but also investigate whether it can be enhanced for use with poultry, having removed the bulk of the fibre. We believe that there is scope for novelty in the use of explosive decompression in SCCO2 treatment, to open up the grain structure to enzyme action.
In the second part of the programme we will develop new metabolically versatile bacterial strains able to degrade most of the non-starch carbohydrate and convert it to 1-butanol, and selective proteolytic and tandem biocatalytic methods to convert part of the protein to value-added chemical products.

Planned Impact

Who will benefit from this research? This is a full proposal invited based on an outline submission to the IBTI club. As an industry club, the immediate beneficiaries will be the club members who have contributed to its foundation, some of whom have a direct interest in increasing the value of DDGS arising from first generation biofuel production while others have a broader interest in thermophilic bacteria and/or producing chemicals from renewables. In the longer term, if we can gain added value from DDGS such that the economics of first generation wheat to ethanol processes are improved, a second group of beneficiaries will be UK farmers who will gain a stable alternative market for their feed wheat. Given that we intend to produce additional products from the DDGS, including running a second fermentation, this will dramatically improve the greenhouse gas balance of a "wheat to ethanol + other products biorefinery". Through displacement of the use of fossil hydrocarbons for this purpose, the wider environmental benefit will help UK government reach its mandated targets and, more importantly, help reverse the trajectory of global warming which threatens social and economic disruption. In addition, the residual material that will be produced is likely to be of increased feed value for pigs and poultry compared with traditional DDGS because of its reduced fibre content. This will enhance its value as a protein supplement in pig and poultry diets and thereby reduce the reliance of the animal feed industry on imported soyabean meal. This will further increase the environmental benefit of UK-based wheat to ethanol production.
How will they benefit? Industrial club members of IBTI will benefit via a number of routes. Firstly, club members have first refusal on the right to license an IP arising from the programme. Secondly, they will get the opportunity to see documents prepared for publication in advance of submission. In this way they will get a unique opportunity to secure any unforeseen IP contained in the work. Finally, by attending dissemination meetings (see below) they will gain access to early stage results in the research programme, which could assist their own research. This benefit could be realised within the next 5 years. UK farmers will benefit through market stabilisation and subsequent long term supply contracts, giving them the confidence to expand their activities, potentially in a 5-7 year timeframe. The global development of biorefineries which supplant fossil fuel usage and some imports, will ultimately benefit us all by reduction of net CO2 emissions. The timescale of this depends on other factors, outside of our control. PDRAs on the project will gain valuable experience on working on feedstocks in the context of a biorefinery and the interdisciplinary nature of the team.
What will be done to ensure that they have the opportunity to benefit? IBTI runs meetings at 6 monthly intervals where the results of IBTI funded research are presented under an agreement of confidentiality. This provides early access for IBTI club Industrial members to arising results. IBTI club members will also get sight of any documents planned for publication, 4 weeks prior to submission. We will also use the forum of IBTI meetings to explore the opportunity to add value to this work by internal collaboration with IBTI funded groups, and use our links in BSBEC to look for further synergies, given the overlap between biofuel production and chemicals from biomass.
Any IP arising from work done within the programme will be secured by Imperial Innovations on behalf of the consortium members. Funding through IBTI will create a contractual obligation to offer licences to IBTI club companies in the first instance and, given their remit, Imperial Innovations will actively pursue the possibility of licensing the technology as rapidly as possible. The PI and CoIs all have experience of working with Industry (see Pt1A of the proposal).
 
Description Distillers dried grain and solubles (DDGS) is a dried by-product from distilleries with value as a ruminant feed. It has limited use in other feeds due to issues related to its high fibre content. With the dramatic increase in "first generation" biofuel production facilities using grain starch (wheat or maize), the quantities of this by-product have increased in recent years. In the UK, at least 2 large-scale wheat to alcohol plants are currently operating. These 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 of protein (35-42%), sugars (35-44%) and oil (4-6%). Wet DG (without the expensive drying stage) has a similar chemical composition. Fractionating wet DG rather than its dried version (DDGS) would save a lot of energy, time and costs to distilleries. This project aimed to use wet Distillers Grains (wet DG) for fractionation, recovery and valorisation of valuable components, which would save the high energy costs involved in DDGS production. Due to the difficulty in obtaining wet DG (WDG) at the beginning of the project, we started with reconstituted DG (rDG), ie DDGS which has been washed to remove the solubles and mimic wet DG. The DDGS (10% moisture content) was sourced from Vivergo biofuels, UK through AB Agri (an animal feed distribution network) and HGCA. Wet DG was finally sourced towards the end of the project and the optimised methods of extractions used in rDG (composed of 40% protein, 4.5% oil, 14.6% glucose, 20.1% hemicellulose and 9.48% arabinose) were applied to the wet DG (28.93% protein, 9.17% oil, 15.1% glucose, 16.61% hemicellulose and 8.4% arabinose). The wet DG was sourced from Ensus through HGCA, and came in as a 28% dry solids material (72% moisture content), with a lower protein and higher oil content than the original DDGS from Vivergo, suggesting that it was a mixed wheat substrate.
The initial hurdles in this project were the sourcing of wet DG and optimisation of the sequence of extractions/fractionation in order not to compromise the other biomass components. After several trials, a sequence that started with supercritical CO2 extraction of oil, followed by alkaline ethanol based extraction of some protein followed by the production of bioethanol from the high sugar fraction post steam explosion and hydrolysis, with the remaining solids tested as an improved animal feed was found to be the most economical and practical.
1. Supercritical CO2 extraction of oil from wet DG and rDG was optimised at University of Birmingham in a bench top reactor, while a bulk extraction process for both materials were also done at pilot scale at Bangor. The optimisation studied the effects of pressure, temperature, addition of co-solvent, moisture content and CO2 flow rate on oil extraction. The optimal extracted up to 99% of the available oil in rDG and 74% of that in wet DG. This extraction was also optimised on wetted rDG (30-50% moisture content), with similar results without the loss of proteins and sugars. The wet DG sample from Ensus had a higher oil content (9.17%) compared with the DDGS and rDG (4.2%). This material was later confirmed to be a mix of wheat and corn. The optimised process for oil extraction from rDG was P=300bar, T=70°C, 10% Ethanol, 50% moisture, 1kg/hr CO2 flow rate. This process removed between 74% and 99% of the oil in rDG. At the pilot scale, supercritical CO2 oil extraction in Bangor, this condition was changed to P=300bar, T=70°C, 10% Ethanol, 30% moisture, 0.3kg/hr flow rate for economy of the process which also delivered similar oil extraction results. The extractions maintained the sugar and protein content during oil extraction with supercritical CO2.

2. The second process (alkaline/ethanol based) involved the removal of some easily extracted protein (at UCL) from de-oiled DG or de-oiled wet DG in order to deliver a concentrated sugar stream, without affecting the sugar ratio of DG or wet DG. Optimisation of contact time, temperature, NaOH and ethanol concentrations were carried out. Optimise conditions could remove between 25% and 70% of the protein, but we chose to go with the 25% protein removal (40 oC, 0.2 M NaOH and 10% Ethanol) in order to minimise sugar release and leave behind some high protein feed material at the end of sugar extraction. The addition of protease extracted the highest amount of protein, while the ratio of released amino acids corresponded to that expected for UK wheat DDGS suggesting non-selective protein release of the major Gliadin and Glutenin proteins. The protein extraction process also helped in concentrating the sugar fraction in DG from 40-44% in the starting material to 62% in the oil and protein extracted DG and wet DG. This sugar concentration makes fractionated DG a competitive candidate for biofuel production, as it is then comparable to various lignocellulosic biomass like wheat straw, miscanthus and barley straw which have a total sugar composition of between 60% and 75% w/w. DDGS would never make a good biofuel biomass without fractionation as higher concentration of DG would be required to deliver an economic level of sugar for biofuel, which will produce some mixing, viscosity and hydrolysis issues.

3. The third process in the sequence was steam explosion pretreatment, enzyme hydrolysis and fermentation of the biomass post oil and protein extractions. The protein extracted DG and wet DG with high sugar content, and reduced protein content was converted to bioethanol and enhanced animal feed at University of Bath. This process was optimised to be mild enough to expose the polymers to a better enzyme hydrolysis which produces the required sugars for fermentation without the release of highly toxic compounds that may reduce fermentability. The process was also mild enough to preserve the protein quality of the remaining solids which was used in feed trials and confirmed to be comparable to other non-extracted DDGS materials in amino acid composition. Biofuel production from wastes normally follow the process of pre-treatment, enzyme hydrolysis and fermentation. After pre-treatment several oligomeric sugars were released. These processes were optimised, and the best pre-treatment for non-extracted rDG was 183°C for 10 minutes, but post extraction, the material became more heat labile, making it possible to do the pre-treatments at much lower temperature and shorter time (165°C, 5 minutes). The pre-treated DG was further hydrolysed with 15 Filter paper Units (FPU) of Cellic CTEC2 (cellulase) to monomeric form before fermentation using a thermophilic industrial Geobacillus or a xylose utilising yeast sourced from DSM. Between 15.4 and 26.1g of ethanol per 100g of biomass was produced from extracted DG. This means that up to 261g of ethanol can be produced per kg of extracted DG. The extracted, pre-treated and hydrolysed DG was fermentable by both Geobacillus and C5 yeast, with very high yields on sugars utilised. Reducing the enzyme hydrolysis time from the standard 72hrs (22.336g ethanol/100g DG) to 6hrs (19.85g ethanol / 100g DG) produced a comparable ethanol levels with C5 yeast fermentation, while 24hr and 48hr hydrolysis produced 21.3g and 22.48g ethanol per 100g DG respectively. This shows that a lot of cost saving can be expected from this optimised process.

4. We (University of Reading) have conducted a 0-10 days feeding trial using chicks fed on a feed concentrate containing wet DG as control and extracted wet DG (EDG), and then rDG as a control for extracted rDG (ERDG) at. There were eight replicate pens (two birds per pen) fed each diet, and diets were formulated to meet the birds' requirements for metabolisable energy, lysine, methionine and threonine. The inclusion rate of the test feeds was 80 g/kg (on an as fed basis). In a fifth treatment ,a control diet which used rapeseed meal instead of the DDGS products was also fed to some chicks. Rapeseed meal was selected because it is another UK home grown protein and has a similar protein content to the DDGS products. Analysis of the birds for nitrogen and gross energy to determine nitrogen and energy retention were carried out. Samples of caecal contents (pooled across two pens, so n=4 per treatment) for metagenomics analysis to determine whether the DDGS has had a significant effect on the caecal microbial population in the very young chick were also analysed. Feeding trial results also suggests that the enhanced materials (ERDG and EDG) behaved like rapeseed meal (when balanced for energy and amino acids). More energy was retained when we fed the enhanced material. Nitrogen retention was greater with the original fresh material, but that was probably because, although similar in amino acid composition, the crude protein content of that diet was lower. We looked at the caecal microbiome of the birds that were fed these diets and the RDG was very different from the others, having a higher proportion of clostridials. That wasn't reflected in any difference in bird performance, though. In terms of bird growth and feed intake, there was no effect of treatment, showing that the enhanced extracted materials are useful animal feeds and that the extractions have not had any negative effect on the feed quality of the remaining material. This feeding test confirms that our extraction process is viable in delivering a final solid material that can be used in animal feed and also in monogastrics, and being able to feed 0 day old chicks with this material shows that they will perform better when fed to older birds.

5. Techno-economic analysis of the extraction process has been performed based on a platform originally developed for the biopharma industry. This showed that the most cost sensitive part of the process was the initial supercritical CO2 extraction, but this assumed that all components were being bought externally. In an existing first generation biorefinery, CO2 and ethanol are readily available and recoverable, which would reduce the costs of the oil extraction step considerably, making the process designed, economic
Exploitation Route We have devised a set of steps to recover value from wet distillers grains and shown this to be economic. This should be of value to first generation ethanol producers and we will be discussing this with Vivergo
Sectors Manufacturing, including Industrial Biotechology

 
Description Results of this work have been picked up by the brewers, Molson-Coors, who are interested in developing a similar process for brewers grains,
First Year Of Impact 2015
Sector Agriculture, Food and Drink,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description P2P NIBB
Amount £63,000 (GBP)
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 05/2016 
End 11/2016
 
Description Techno-economic modelling of DDGS process
Amount £27,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2016 
End 03/2017
 
Description Valorising Brewers Spent Grain 
Organisation Molson Coors
Country United States 
Sector Private 
PI Contribution Application of the methods developed during the DDGS project to the valorisation of brewers spent grain, with a specific focus on generation of functional polysaccharides
Collaborator Contribution Molson-Coors supplies spent grain, Unilever analyses polysaccharide fractions for functionality
Impact This is a NIBB-funded POC project which has just started
Start Year 2016
 
Description Valorising Brewers Spent Grain 
Organisation Unilever
Department Unilever Research and Development
Country United Kingdom 
Sector Private 
PI Contribution Application of the methods developed during the DDGS project to the valorisation of brewers spent grain, with a specific focus on generation of functional polysaccharides
Collaborator Contribution Molson-Coors supplies spent grain, Unilever analyses polysaccharide fractions for functionality
Impact This is a NIBB-funded POC project which has just started
Start Year 2016
 
Description Work with Greencore on application of waste sandwich bread 
Organisation Greencore Ltd
PI Contribution Work on Business Interaction Voucher (Food waste Net) sponsored research to valorise waste bread
Collaborator Contribution Provision of materials and data
Impact Report to FWN, successful completion and application for follow on funding
Start Year 2015
 
Description Popular Science (Bath) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Pint of Science - interactive 30 min presentation followed by Q &A in a local pub
Year(s) Of Engagement Activity 2016
URL http://www.bath.ac.uk/news/2016/04/18/pint-of-science-2016/