Food, feed and fermentation
April 01, 1996
by Teresa Acklin
The second of two parts takes an in-depth look at potential uses for grain and flour in the biotechnology sector.
Of all nonfood uses of cereals, the most exciting prospects for the future surely lie with the fermentation industry. Inextricably linked to the biotechnology revolution, the fermentation industry is poised to become the supplier of an almost limitless range of products, including new items and replacements for products based on non-renewable materials and environmentally harmful processes.
The most common source of both energy and carbon for fermentation is sugar (usually as glucose or sucrose). This is often supplied as molasses, a low priced byproduct of the sugar industry.
However, as the fermentation industry grows and the sugar industry declines, in part due to competition from cereal derived glucose and fructose syrups, a tendency towards alternative sources of carbon is surfacing. Of the alternatives, cereal crops are widely considered to offer the greatest potential. The accompanying table lists some of the products of fermentation that could be produced from cereal-based raw materials.
Indeed, cereal starches already are used extensively in the fermentation industry. Although starch is not in itself a readily fermentable material, it is relatively easily hydrolyzed to glucose.
Cereals are more energy intensive than sugar crops and have the advantage of being more easily storable and transportable. In addition, as whole grains, they contain virtually all the nutrients required to support the majority of microorganisms and so, in principle, require little supplementation of nitrogen, phosphorus, etc.
It is therefore possible to foresee a future in which some industrial products, such as oil and starch, will be extracted directly from grain, and others will be produced by fermentation of grain flour.
A total processing concept can be envisaged in which wheat is milled primarily to produce flour for food use, but with lower value streams being taken off for processing to nonfood products rather than being blended into higher value streams. Of course, central to the nonfood process would be a fermentation plant.
A key to the success of this approach would be the production of a generic fermentation medium from which a whole range of fermentation products could be produced. This generic medium could itself be produced by fermentation.
It is current practice (and therefore economically acceptable) in some fermentation industries to buy starch that has been extracted from cereal grains and subsequently hydrolyzed to glucose for use as a carbon/energy source. The starch hydrolysis is carried out using enzymes, which have themselves been produced by fermentation.
A nitrogen source, often in the form of maize steep liquor (a byproduct of maize starch extraction) must be added to the starch-derived glucose. The mix is then supplemented with additional minerals and other nutrients, which may well have been present in the original grain, to provide a complete fermentation medium.
Thus, the total cost of the medium must include costs associated with starch extraction, enzyme production, starch hydrolysis and nutrient supplementation. All this to arrive at a medium which is equivalent to whole grain flour!
GLOBAL RESEARCH UNDER WAY. The Satake Centre for Grain Process Engineering at the University of Manchester Institute of Science and Technology, U.K., is conducting research into the production of a generic fermentation medium based on whole wheat flour. To date, results have been extremely encouraging, and a process has been developed that produces separate glucose- and nitrogen-rich streams suitable for use in subsequent fermentations (see figure).
Lund University in Sweden is working on one particular process that produces lactic acid by fermenting hydrolyzed whole wheat flour. The optically pure L-lactic acid can then be polymerized into poly L-lactic acid (PLLA), a biodegradable substitute for petroleum based polymers.
Another process, already developed at Purdue University in the U.S., takes maize starch as a feedstock for the fermentation production of catechol using genetically engineered E. coli bacteria. Catechol is used to produce vanilla flavorings and adipic acid, a key ingredient in nylon manufacture. Both would otherwise require benzene as a starting point. Workers at the Latvian University in Riga, Latvia, using a closed system approach, have successfully produced lysine, polyhy-droxybutyrate (PHB) and ethanol from wheat grain.
Of course, for biochemists at least, ethanol is the classic fermentation product. In the processing sense, ethanol fermentation is rather more straightforward than most and yields a product that could replace gasoline as a motor fuel.
For these reasons ethanol has for many years been the prime target for researchers and supporters of the renewable resource revolution. It has also been the prime target for their opponents: so much so that, for many, renewable resources and gasohol are synonymous, and the future for all bioproducts is judged against the present day economics of gasohol production.
Generally, this gives both gasohol and renewable resources a bad press. It is all too easy to dismiss gasohol and other renewables on the basis that they require heavy subsidies to work.
But ever since Brazil instituted its fermentation alcohol based fuel economy more than a decade ago, more and more gasohol programs have been launched around the world. However artificial the economics might be at present, there is no doubt that industry, through improvements in technology, has a knack of reducing processing costs and that the situation will improve in the future.
A CLEANER ENVIRONMENT. Environmental issues, which help to keep bioethanol programs alive, are also helping to establish a new range of products based on biodegradable plastics. This is a particularly interesting area in which both fermentation of cereals and other forms of cereal processing can play a major role.
The two fermentation routes to such products involve the production of PHB and PLLA. Both are commercial products, but are very expensive, and current production is only in the order of 1,000 tonnes per year.
Nonfermentation based biodegradable plastics use starch, either as a filler or more recently in the form of thermoplastic starch. As a filler, starch is simply added to conventional polymer mixes, which subsequently fall apart when the starch degrades, leaving the nonbiode-gradable material disintegrated but chemically intact.
The ability to render starch thermoplastic, however, provides the prospect of a truly biodegradable plastic incorporating up to 95% starch. Considerable development work in this area has been carried out by the U.S. Department of Agriculture's National Center for Agricultural Utilization Research.
Unfortunately, starch is a hygroscopic polymer and gains or loses water to achieve equilibrium with ambient air. As a result, properties of materials made with starch (including thermoplastic starch) change with relative humidity. To help alleviate the problem, biodegradable water repellent coatings are being evaluated.
Another approach being used by the U.S. research center is to produce biodegradable composites of starch and polyhydroxybutyratecovalerate (PHBV) copolymers. Again, the starch is effectively a low cost biodegradable filler that is incorporated into a biodegradable material. It is hoped that this approach will help PHBV plastics achieve greater market penetration, which has so far been limited because of their high cost relative to commodity thermoplastics.
Starch, while it will always be the basis for the majority of industrial products from grain and flour, is not the only useful component. Gluten proteins can also be used in the production of plastics in the form of biopolymer films. Workers at the U.S. University of Nebraska-Lincoln estimate that a substitution of 30% wheat gluten polymer in agricultural mulches and trash bags would use around 230,000 tonnes of gluten in the U.S. alone.
New products are also being developed from bran components. At GB Biotechnology in the U.K., three products from maize bran have been developed: a soluble arabinoxylan ferulate that can be converted by catalytic oxidation into a gel (commercially called SupaGel), a mix of soluble hemicellulose gel that has adhesive properties (commercially called Z.Sol) and an insoluble cellulosic polysaccharide (commercially called ZGel) that has gel properties on shearing.
These are but a few of the potential products from grain and flour. If the possibility of incorporating crop residues is considered, the concept of total processing becomes an attractive prospect. Research at the Silsoe Research Institute in the U.K. suggests that whole crop utilization through a biorefinery is competitive with conventional agricultural systems for wheat grain and straw processing.
So the future looks bright for grain producers and processors. But what are the real implications?
First, estimates indicate that the absolute maximum nonfood utilization is around 10%; but more realistically, we can expect to see just 2% or 3% of cereal crops being used in this way.
Second, it is difficult for the chemical industry to develop successful processes if they must compete with the food industry for raw materials. This suggests that crops should be grown intentionally for nonfood use and, therefore, bred for that purpose. This will not happen, without government intervention, until both industry and agriculture develop a real commitment. Both must believe in the future for nonfood uses.
Fortunately, governments around the world, particularly those in Europe and North America, are encouraging industry, agriculture and researchers to come together to develop suitable processes. There is little doubt then, that as the third millennium unfolds, an increasing proportion of our daily needs will be met, not just through grain-based foods, but also through grain-based chemicals.
Dr. Colin Webb is professor of grain process engineering and Director of the Satake Centre for Grain Process Engineering at the University of Manchester Institute of Science and Technology (UMIST). U.K.Potential fermentation products from cereal grains
| ||Poly L-lactic acid (PLLA)|
| ||Glucose Isomerases|
| ||Penicillin acylases|
|Ergot Alkaloids (Lysergic acid)|
|Food & Drinks||Beer, wine, etc.|
|Single cell protein|