Industrial enzymes

Why enzyme biotechnology is increasingly important for modern industries

Many people may be vague about the actual definition of “molecular bioscience” and what it does for the community. A prime example of biomolecules being used in our day-to-day lives – both on a domestic and an industrial scale – is enzymes.

What are enzymes?

Enzymes are biological catalysts: proteins, made in the cells, which speed up all the chemical reactions inside all living organisms. They do this by binding to substrates (chemicals involved in a metabolic reaction) and lowering the activation energy needed either to build them up into larger molecules, or to break them down into smaller ones¹.An example of an enzyme-based reaction is the breakdown of starch into glucose by amylase enzymes in the saliva.

The part of an enzyme which binds to a substrate is called its active site. The active site is very specific in structure and will only bind to a particular substrate – a bit like a key fits into a lock (in fact, this is known as the “lock-and-key” model²). Because of this, living organisms need a vast number of different enzymes – one for every chemical reaction that takes place inside the body!

Why are enzymes used so much in industry?

The use of enzymes for manufacture goes back to about 8,000 years ago³ – when humans first used yeast to ferment grapes into alcohol. In the absence of oxygen, the yeast enzymes would break down glucose into ethanol and carbon dioxide. This batch process for the production of ethanol is still used today. At the time, of course, there was no understanding of enzymes and this was merely experimental. However in modern days, as our understanding of molecular biosciences and biotechnology has improved, we have been able to exploit the properties of enzymes to use them quite diversely.

Enzyme biotechnology really took off in the 1950s. Examples of enzymes used in industrial processes include:

·         Sucrase enzymes in soft-centred chocolates

·         Proteases and lipases in baby food to start pre-digestion

·         Biological washing powders to break down stains into soluble amino acids/fatty acids

·         Pectinase in fruit juice to increase yield and make the juice clear

·         Yeast enzymes in the fermentation of sugar

·         Rennin used to coagulate cheese

·         In the textiles industry to enhance the preparation of cotton⁴

·         Esterase enzymes to remove adhesives for the recycling of paper

The list really does go on. Enzymes as a form of biotechnology are growing rapidly: Figure 1 shows the projected growth of the global industrial enzyme market up to 2015. Why are enzymes so attractive to industries?

Global industrial enzymes market, $ millions5	Estimated value in 2010	Predicted value in 2015	% increase
Technical enzymes	1000	1500	50
Food and beverage enzymes	975	1300	33

Figure 1: the global industrial enzymes market is expected to increase at a compound annual growth rate of 6%

The use of biological catalysts to speed up industrial reactions is often favoured over the use of metal catalysts for two main reasons.

Firstly, enzymes operate at fairly low temperatures and pressures, which keeps costs down. Typically the temperatures required by enzymes are about ten times lower than those required by inorganic catalysts! In addition, enzymes can be up to 10,000 times more efficient than ordinary chemical catalysts, so profit is maximised.

What are the drawbacks of enzyme biotechnology?

Figure 2: enzyme activity increases

 with temperature up until the 

optimum – then it denatures.⁶

Okay, so enzymes aren’t 100% ideal – there are drawbacks to using them. The main one is that the 3D structure of enzymes is so fragile and thus largely sensitive to changes in temperature and pH. Figure 2 shows a graph of enzyme activity against temperature. As with all chemical reactions, the rate of an enzyme-catalysed reaction increases with temperature – up to a point. The polypeptide chains in proteins are held together by weak intermolecular forces (known as van der Waals forces and hydrogen bonds). At a certain temperature – often around 42⁰C – these weak forces are overcome and the structure of the enzyme’s active site changes. This means that the substrate can no longer bind to the enzyme, which is now said to be denatured. Denaturation is an irreversible process, so industries must regulate temperature very carefully. Note from Figure 2 how the optimum temperature of an enzyme (the temperature at which it has the highest rate of activity) is just below the point where it denatures – about 37⁰C. There is a very fine balance to be struck, therefore, between increasing the rate of a reaction and not permanently denaturing the enzymes which are catalysing it.

Sharp changes in pH also cause the denaturation of enzymes because functional groups in the active sites can lose hydrogen ions in a solution which is too alkaline and gain them in a solution which is too acidic. This means that the substrate can no longer bind to the active site. Different enzymes have different optimum pHs and so this can be harder to control than temperature.

Other issues which arise are the cost of extracting enzymes and the difficulty in reusing them. Enzymes are usually extracted from micro-organisms which are grown economically in bulk fermenters⁷. However, this is not a cheap process, and because enzymes are combined with substrates in an aqueous solution it can be costly to separate and reuse them as well.

Since the 1960s⁸ industries have employed a technique which resolves all of the aforementioned problems: immobilisation. By this method, the enzymes themselves are trapped in an insoluble material such as fibrous polymer mesh, and packed into a column through which the substrate can be continually fed. There are numerous advantages to immobilising enzymes:

·         The enzymes are more stable, so they are less likely to be denatured. This also means that higher temperatures can be used, increasing the rate of reaction.

·         The enzymes can easily be recovered and reused, making immobilised enzymes a more cost-effective method.

·         The enzymes do not have to be removed from the product and do not contaminate it.

·         Since the products are separated from the enzymes, there is no “feedback inhibition” – where products bind to the active site and prevent more substrates from reacting.

However, another issue of the application of enzymes cannot be addressed by immobilisation. In the 1970s evidence arose that proteases used in biological detergents could break down keratin in the skin and lead to skin irritation⁹. Although this has not been scientifically proven many people claim to have skin sensitive to biological detergents.

Enzymes in the future?

Over time, the use and efficiency of enzymes in industry has increased rapidly and they are now used in a diverse range of industries, from textiles to tendering meat¹⁰. Of course, there is still room for development and as research continues into how the efficiency of enzymes can be improved, enzymes will be put to new uses and new ones will continue to be discovered¹⁰. A current area of research is into enzymes which can withstand greater extremes of temperature, which would be particularly desirable in laundry and industrial processes where high temperatures are needed.

Who knows what developments the future will bring; however, it can be said with reasonable certainty that the enzyme industry is one which will continue to grow and develop.

References

1.  Life Study: A Textbook of Biology by D. G. Mackean
2. A2 Level Chemistry: The Revision Guide (CGP)
3. http://www.absorblearning.com/chemistry/demo/units/LR1507.html
4. Enzyme Biotechnology in Everyday Life by Theresa Philips
5. http://www.bccresearch.com/report/enzymes-industrial-applications-bio030f.html
6. http://www.rsc.org/Education/Teachers/Resources/cfb/enzymes.htm
7. www.spolem.co.uk/worksheets/docs/industrial_enzymes.doc
8. Carrier-bound Immobilized Enzymes: Principles, Application and Design
9. New GCSE Biology by Gemma Young and Sarah Jinks
10. http://prof.dr.semih.otles.tripod.com/enzymesused/enzymesused.htm
11. 11. Semih Otles, Professor of Food Chemistry