Biotransformation Technologies

Figure 1: steroid Hormones

Popular biotransformations throughout history

have included utilising yeast to convert glucose to ethanol and CO2, the use of lactic acid bacteria to make yoghurt and the employment of the fungusAspergillus niger to make citric acid. More recent biotransformation technologies, however, have become more sophisticated, involving such procedures as the production of pharmaceuticals and the development of methods to reduce environmental pollution.

Biotransformation Technology in the Production of Steroid Hormones

Steroid hormones ( fig.1) are important therapeutic drugs, as they assist in various metabolic functions in the human body. Manufacturing these chemicals involves many steps and the costs involved can be exorbitant. Recent use of micro fungi and bacteria to carry out some of these steps has proved to be extremely efficient and cost effective.

Examples include using the fungus Rhizopus arrhizus to convert progesterone to 11- hydroxy progesterone and finally to cortisone (fig.2), which is an antiarthritic drug. In this process, progesterone is added to a fermentation tank containing the fungus, which hydroxylates the progesterone at the number 11 carbon atom in its steroid ring.

Such a hydroxylation step would otherwise be laborious and expensive using synthetic methods alone. Further chemical synthesis steps are then used to convert 11-hydroxy progesterone into cortisone. The incorporation of biotransformation technology into this process has reduced the cost of cortisone production in the U.S. by a factor of around 400.

Researchers at the Tehran University of Medical Sciences have also investigated the biotransformation properties of the fungus Nerospora crassa, which can transform the steroid hydrocortisone into a pregnane and androstane derivative by removing the hydroxyl side chains from the molecule. This has commercial potential, as drugs in this family are used to treat endometriosis and other hormonal conditions, and can also act as anti-inflammatory agents.

Biotransformation in the Production of Antibiotics and Vitamin C

Biotransformation technologies are not limited to the production of steroid derivatives. New, more effective antibiotics, for instance, can be manufactured from existing ones using microbe-mediated transformations. Examples of this include penicillin and cephalosporins, which can be deacylated by microbes to produce semi-synthetic varieties of the original antibiotics.

In addition, the bacterium Acetobacter suboxydans can be used in the production of ascorbic acid (vitamin C), by transforming D-sorbitol, a derivative of glucose, to L-sorbose. L-sorbose is then chemically transformed to ascorbic acid.

Biotransformation and the Environment

A study by Lai, Scrimshaw and Lester (2002), has found that the algaChlorella vulgaris, can transform both natural and synthetic oestrogens. The syntheric oestrogen, oestradiol valerate, was shown to be transformed to oestradiol, and the natural oestrogens oestradiol and oestrone were also converted to related compounds in the presence of the alga.

This has environmental significance, as it throws light on the ability of microbes to detoxify various pollutants present in sewage and other runoff. Indeed, some macroalgae have been nicknamed ‘green liver’, as they have similar detoxifying enzymes as the human liver. Other algal species are capable of transforming heavy metal and organic pollutants.

Perhaps one of the more significant recent discoveries in this area has been that of the hydrocarbonoclastic bacteria, which can degrade alkanes as part of their metabolism. This shows potential for the possible biodegradation of oil spills in marine environments. Scientists looking for ways to reduce the recent Deepwater Horizon oil leak are suggesting that naturally occurring bacteria from the Vibrio family are capable of degrading some of the oil.

They are already adding fertiliser to the oil that has reached the shore to promote the growth of these microbes. The introduction of additional oil eating bacteria such as Alcanovirax borkumensis is also being considered.

Other examples of such ‘bioremediation’ include using microbes to detoxify compounds present in pesticides and raw sewage in both soil and water ecosystems. The US Geological Survey (USGS), for instance, has been researching the biotransforming effects of microbes such as the bacterium Dehalococcoides ethenogenes on chloroethenes, common contaminants of groundwater systems. These microbes are able to convert chloroethanes to safer,less chlorinated compounds.

Biotransformation Companies and the Future

The Biotech company, Spi Bio is an example of the commercial application of biotransformation technologies. This organisation advertises services that include the production of metabolites by bacteria, filamentous fungi and yeasts, which mimic the chemical pathways present in the mammalian cytochrome system.

Biotransformation technologies have obviously come a long way since the early use of yeasts and bacteria to make bread, wine and yoghurt. With the millions of species of bacteria and fungi on the earth the possibilities for utilising their biochemical pathways to our own advantage are virtually endless.

References

Fathabad, Yahzdi, Faramarzi, and Amini, 2006, ‘Biotransformation of Hydrocortisone by Neurospora crassa’ Journal of Sciences, University of Tehran, sid.ir, accessed 4/6/2010

Lai, Scrimshaw and Lester, 2001, 'Biotransformation and Bioconcentration of Steroid Estrogens by Chlorella vulgaris', Imperial College of Science, Technology and Medicine, London, asm.org, accessed 3/6/2010

SPI BIO Bertin Group, 'Generating New Chemical Entities Using Biotransformation Technology' spibio.com, accessed 4/6/2010

Figure 2: Cortisone

USGS, 2008, Microbial Degradation of Chloroethenes in Groundwater systems, toxics.usgs.gov, accessed 2/6/2010

Pasteur and Koch: Investigating the Causes of Infectious Disease

Louis Pasteur

The work of both Louis Pasteur and Robert Koch established conclusively that microorganisms are the cause of infectious diseases.

Prior to the work of Louis Pasteur (1822-1895) and Robert Koch (1843-1910), many scientists promoted the ‘spontaneous generation’ theory as a way of explaining the appearance of microbes in spoiling food and rotting organic matter. This theory, championed by naturalists such as John Turberville Needham and Georges- Louis Leclerc, suggested that microbes and other life forms appeared from nowhere and proceeded to multiply on any available food source.

Pasteur’s studies, however, inferred that microbes such as bacteria, fungi,viruses and protozoans were already present in organic material and multiplied when conditions became favourable to them. This ‘germ theory’ explanation for food spoiling, fermentation and disease was reinforced when Robert Koch’s famous postulates helped to prove how a specific microorganism could cause a particular disease.

Pasteur and Fermentation

Despite his initial work in the field of stereochemistry, Louis Pasteur is more commonly recognised for his contributions to microbiology. As Professor of Chemistry at the University of Lille, Pasteur was asked to investigate the production problems of some of the local beer and wine industries. After careful microscopic investigations, he concluded that a specific microorganism was responsible for different types of fermentation.

Wine and beer, for instance, were the fermentation products of members of the yeast genus Saccharomyces, whereas their souring was due to the presence of bacteria such as Lactobacillus and Acetobacter. Pasteur’s subsequent realization that heating the wine or beer to around 50- 60 degrees Celsius could destroy these microbes helped to solve many of the spoilage problems in these industries.

The Link Between Microbes, Food Spoiling and Disease

This process, which became known as ‘pasteurisation’, is still used today in the food and milk industries. Although Pasteur’s initial intention was to prevent spoilage in wine and beer, pasteurization can also help to remove disease-causing organisms that may be present in food. Pasteurising milk, for instance, can destroy microbes that cause tuberculosis, brucellosis, diphtheria, scarlet fever and salmonella poisoning.

Pasteur’s famous ‘meat broth’ experiment in 1862 further strengthened the idea that food spoiling is a result, rather than a side effect, of microbial contamination. In this experiment he used two flasks containing equal amounts of meat broth. One flask had an open neck while the other had a curved, ‘swan-like’ neck that could trap any particles in the air before they reached the broth.

After boiling the broth in both flasks and leaving them for a period of time, he found that only the broth in the open-necked flask had become spoiled. This suggested that something from the air had caused the contamination, thus disproving the theory of spontaneous generation.

Pasteur first demonstrated the link between microbes and disease in 1865 when he isolated the microscopic parasite (Nosema bomycis) that was killing silkworms throughout France. By recommending that only uninfected eggs be selected for farming, he helped to save the industry in France and other parts of Europe.

Further Diseases and the Germ Theory

Pasteur later applied his ‘germ theory’ to other diseases, identifying the microbes responsible for anthrax, cholera, tuberculosis and rabies. Moreover, in 1879 he discovered that chickens injected with an attenuated (weakened) form of the chicken cholera bacterium were protected against contracting the more virulent form of the disease.

This led to Pasteur’s development of a similar vaccine for sheep anthrax in 1881. A public trial of this vaccine met with resounding success and helped to resolve the anthrax epidemic occurring in France at the time. In 1879 Pasteur also successfully vaccinated a nine- year- old boy with an attenuated form of the rabies virus, heralding the first inroads into preventive medicine.

Robert Koch’s Postulates

Pasteur had shown that microorganisms were present whenever food spoiled or an organism was diagnosed with an infectious disease. He also demonstrated that these microbes did not ‘spontaneously generate’, but were instead ubiquitous in the air and living things, simply waiting for the ideal conditions to reproduce themselves. Pasteur’s insistence on hygienic conditions in the workplace consequently reduced contamination and spoiling in wine and beer and paved the way for the use of aseptic techniques in medical procedures.

However, Pasteur had never decisively linked a microorganism to a particular disease. Koch, a medical doctor, had the necessary background to develop a series of steps that could, indeed, prove this. Initially working with anthrax in sheep, Koch further developed the findings of Casimir Davaine, who had shown that healthy sheep could contract anthrax if injected with the blood of infected animals.

Koch extended this finding by successfully isolating and culturing the anthrax bacillus (Bacillus anthracis) and reintroducing it into healthy sheep and mice. As he predicted, these animals later developed the symptoms of anthrax. Koch achieved similar results after conducting tests with the bacteria that cause tuberculosis and cholera. In 1890 this work led him to present four basic steps required to determine that a particular microbe caused a given disease. Later known as ‘Koch’s Postulates’, they consist of the following rules:

•                The microorganism must be present in all diseased organisms.

•                The microorganism must be capable of being isolated and identified.

•                When healthy animals are inoculated with the microorganism they must develop symptoms of the original disease.

•                The microorganism must be recoverable from these newly diseased animals. It must then be isolated and identified as being the same as the microbe in the original infected animals.

The Legacy of Pasteur and Koch

By 1900, Koch had identified the germs that caused twenty -one diseases, and had developed an improved method of staining cells for use in microscopic studies. He also demonstrated that microbes caused wounds to become septic, making the link, once again, between microbes and infectious diseases.

Both Koch’s efforts, and the work of Pasteur, contributed to the preventive medicine, sanitation and hygiene practices we take for granted today. The spontaneous generation myth had been dispelled conclusively.

References

•                BBC, 2012, ‘Louis Pasteur

•                Encyclopædia Britannica Inc., 2012.'Louis Pasteur.' Encyclopædia Britannica Online.

•                Hani, 2010, ‘Discovery of Pasteurisation’, experiment-resources.com

•                History Learning Site, 2012, ‘Robert Koch’, historylearningsite.uk

•                Shurtleff , W. and Aoyagi , A., 2007, ‘A brief History of Fermentation, East and West’, Soyinfo Centre, California

The History of Biotechnology

Dairy Cow - Zoe Bianchi

The origins of biotechnology can be traced to the beginning of the Agricultural Revolution around 10000 years ago. In its earliest forms it included the collection and sowing of selected seeds, trapping eels, domesticating animals and making wine, beer and yoghurt.

During this period humans began selecting and herding animals with high meat or milk producing qualities. Modern dairy and beef cattle have in fact originated from the primitive Auroch, a long haired animal with large horns. Dairy cattle such as the Guernsey (see figure 1) are the result of years of selecting for high milk production and milk fat content, while meat producing breeds such as the Aberdeen Angus have been selected for high body mass, reduced hair, short horns and red coat colour.

Artificial Selection of Animals 

Other early instances of the domestication of animals include the taming of donkeys in Egypt and camels in South America around 3000 years ago and the cultivation of silkworm moths in China during the same period. Modern day poultry have arisen from the red jungle fowl, which was domesticated around 2000 BC in Asia, while Australian Aboriginals dug channels to connect ponds and trap eels as long ago as 18000 BC. Early farmers often found that hybrid strains of animals and plants often possessed more favourable characteristics.

Artificial Selection of Plants

Wheat has also been artificially selected over thousands of years to produce Triticum aestivum, the bread wheat we are familiar with today. This modern species of wheat arose from a hybrid strain, Triticum turgidum (also known as Emmer wheat), which was itself the result of the hybridisation of Triticum monococcum and wild Triticum. Hybrid plants are usually sterile but Emmer wheat arose from a meiotic error in one of the initial hybrid plants.

This resulted in a plant with duplicate sets of chromosomes from each species which could now undergo meiosis to produce gametes. Further breeding experiments such as those carried out by Australian William Farrer have produced wheat with favourable characteristics such as rust and drought resistance, short stalks and high yielding ears.

Corn, first cultivated in South America, has also been selected over the years for favourable traits such as colour, size, flavour and cobs with large numbers of seeds that mature on the stem. Traders introduced corn into Europe in the 15th and 16th centuries.

The Use of Fermentation in Early Biotechnology

Early biotechnology also took advantage of the natural metabolic processes of various microorganisms to produce wine, beer, bread, yoghurts and cheeses. When yeasts break down sugars in respiration, carbon dioxide and ethanol are produced. Wild yeasts naturally present in fruit were therefore used in the production of wine from around 2000 years ago in Egypt and Assyria, while yeasts present in germinated barley were used to produce beer as early as 6000 years ago in Egypt, Mesopotamia and Greece.

Lactic acid bacteria, naturally present in milk, also break down sugars in respiration, but the product of this reaction is lactic acid. This process was first used to produce yoghurts and cheeses in the Middle East several thousand years ago. Australian Aboriginals also fermented the nectar of native flowers to produce a sweet beverage and used fermentation to remove the natural toxins in cycad seeds.

Another type of microbe, Acetobacter, converts ethanol to acetic acid (vinegar) in the presence of oxygen. This natural souring of wine was observed thousands of years ago, with the first recorded use of vinegar as a preservative and condiment occurring in Babylon in 5000 BC.

Fermentation and Modern Technology

With the development of the steam engine in 1775, fermentation equipment could be sterilised and more elaborate machines could be made to produce wine, beer and other products on a large scale. The invention of refrigeration also allowed large quantities of alcoholic beverages and other fermentation products to be stored for longer periods of time.

The development of the microscope allowed scientists such as Louis Pasteur to make a definite connection between microbes and their respiration products: yeast, for instance, was found to be necessary for the production of ethanol and lactic acid bacteria were found to be necessary for the production of yoghurt.

Moreover, research into the growth and nutrition requirements of different types of microbes enabled optimum cultivation conditions for these organisms to be established in specialised ‘bioreactors’. Bioreactors are large steel vats which are supplied with the specific nutrient, aeration and temperature needs of particular microorganisms.

In the production of citric acid, for instance, the fungus Aspergillus niger is grown in a bioreactor on a molasses substrate that is low in iron. In vinegar production the bacterium Acetobacter is cultivated in a bioreactor that is continuously aerated, while the yeast biomass required to produce baker’s yeast is also grown in aerated conditions under strictly controlled temperatures.

Biotechnology Today

In addition to fermentation and the artificial selection of plants and animals, biotechnology today also includes genetic engineering, gene therapy, DNA fingerprinting, the production of monoclonal antibodies and antibiotics such as penicillin, tissue engineering and the production of recombinant vaccines. Although these are more sophisticated than early examples of biotechnology, they are nonetheless instances of humans gaining benefit from the use of living organisms or their processes.

References

History World, ‘History of Domestication of Animals’, historyworld.net, accessed 24/6/2010

Kennedy, Hickman, 2004, ‘Biology in Context, the Spectrum of Life: Biotechnology Option’, Oxford Press

Ptolemy, Alexander, 2009, ‘A Brief History of Vinegar- The Remarkable Liquid’, associatedcontent.com, accessed 25/6/2010

Never Enough - The Story of the Cure

Robert Smith - Nancy J. Price 1985

Written in 2005 and published in 2008, this unofficial biography of the Cure follows the rise of this enigmatic group from their roots in middle class Crawley to their confirmed status as rock nobility some four decades later. The depth of the book reflects Apter’s research skills and extensive knowledge of the music industry.

Although Apter does not manage to interview Smith himself in this book, the many enlightening discussions he has with ex members Laurence Tolhurst, Phil Thornally, Michael Dempsey and producer Steve Lyon help to piece together the fascinating history of the band.

A common thread throughout the book is Apter’s obsession with the surprising duality of musical styles consistently presented by Smith – this was perfected at the height of the band’s commercial success during the mid to late eighties , where the group achieved a balance between melancholic, decidedly boring tracks and well constructed pop tunes.

The Goth Guru and the Pop Tunester

This, as Apter puts it, may well have been the result of Smith hedging his bets in a bid, perhaps, to satisfy both the Cure’s loyal Goth entourage and their growing mainstream audience worldwide. Smith’s involvement with Sioxsie and the Banshees in the post punk era of the early eighties, coupled with his morbid, often drug induced mood during this period (which spawned the Faith album and the even more morose Picture tour), resulted in an output of tracks tailor made for what Apter refers to as the ‘overcoat brigade’.

 Robert Smith- Zoe Bianchi

At the same time, Smith’s discovery that he could compose catchy melodies such as The Lovecats, Let’s Go to Bed, In Between Days , Just Like Heaven and Boys Don’t Cry attracted a whole new cohort of listeners, who also appreciated the slightly dangerous image of the group promoted in Tim Pope’s colourful music videos.

Apter’s account of the backgrounds of Smith and the early members of the group- Tolhurst, Simon Gallup and Dempsey-throws additional light on the band’s peculiar repertoire. All grew up listening to the records of their older siblings and were therefore exposed to rock legends such as Jimi Hendrix, the Rolling Stones, Nick Drake and the Beatles from an early age. The concept of not being cool if you couldn’t sit through all the tracks on an album, even if some were absolute rubbish, may have been instilled in them at this point.

Indeed, although Apter observes that some of the Cure’s albums are so dull they could only be of interest to diehard fans, he, too, gives the impression that he concurs with the ‘suffering for one’s art’ philosophy. This is suggested throughout the book when he refers to the hit singles of many of the Cure’s contemporaries as ‘fluff’: purely, it seems, because they have structure and a melody.

Robert Smith the Strategist

This attitude, which, it could be argued, borders on pretentiousness, has nevertheless struck a chord with millions of record buyers and has allowed Smith to experiment with his music in a way other musicians could only hope for. Apter in fact suggests that much of what Smith has said and done over the Cure’s career has been a deliberate strategy to avoid becoming ‘uncool’ and therefore unviable in the music industry. He believes, for instance, that Smith’s write off of Let’s Go to Bed as ‘junk’, ‘stupid and ‘rubbish’ was cleverly calculated; if this single failed, ‘he could defend himself by dismissing it as a lark. That way, the band’s credibility would remain intact.’

Moreover, Apter believes the disinterested manner conveyed by the group on stage and reflected in their music played a part in their success. Referring to an appearance on television, he states that, ‘they looked and acted bored, but all across the nation (viewers) …..interpreted Smith’s stifled yawns as enigmatic arrogance.’ Indeed, Smith himself admitted that he had not had the courage to express honest emotion in his music until he wrote ‘Lovesong’ for his wife, Mary, in 1989.

Other Cure Members and the Band Today

Although acknowledging that the Cure, throughout its many line-ups, has essentially been Robert Smith’s band, Apter also addresses the sizeable contributions of its other members. Considerable amounts of the text discuss the early creative input of Tolhurst and Dempsey, and the later contributions of Simon Gallup, Porl Thompson, Roger O’Donnell, Boris Williams and Jason Cooper.

The inclusion of former Cure roadie Perry Bamonte in the line-up (along with his fascination for pyrotechnics) also makes interesting reading. Apter also devotes time to Tolhurst’s legal wrangle in 1994 with the band over unpaid royalties, and the highs and lows of his relationship with the band over the years.

Over the last two decades, an era which has been less commercially successful for the group (see Richard Gibson's comments on the band in 2010), the band appears to have mellowed to the point of including such upbeat songs as Mint Car and Wrong Number in recent albums. Of course, the plodding, weird tracks still prevail, but as Smith has admitted, he actually likes repetitive music. Although he has often maintained over the years that he doesn’t care what others think of his music, perhaps, for the first time, he genuinely means it.

Reference

•                Apter, J., 2008, 'Never Enough, The Story of The Cure' Omnibus Press

•                Gibson, R., 2010, '413 Dream by The Cure Album Review', Suite 101.com, accessed 12/6/2010

•                Smith, R., Pope, T.,1985, 'In Between Days', youtube.com

•                Smith, R., Pope, T.,1987, 'Just Like Heaven', youtube.com

The Polymerase Chain Reaction

Fig. 1 - A strip of PCR tubes

The polymerase chain reaction (PCR) makes use of DNA’s natural ability to replicate itself in the presence of the enzyme DNA polymerase. This replication occurs just before cells divide by mitosis and involves the double stranded DNA molecule ‘unzipping’ to form two single strands. Complementary nitrogen bases then line up along each free strand to form two new double stranded molecules.

PCR – A Process That Tolerates Temperature Extremes

The polymerase chain reaction also utilises the fact that DNA will denature (divide into two strands) at high temperatures. In this way, the single strands that form in the first stage of DNA replication can be artificially prepared in readiness for the formation of complementary strands.

Although these and other vital processes occur at different temperatures, in 1985 Kary B. Mullis devised a way in which they could all occur in the same experimental vial (see figure 1) without denaturing the polymerase enzyme. He did this by using the DNA polymerase from a heat resistant strain of bacterium called Thermus aquaticus . In this way, temperatures during PCR reactions can range from around 55°C to 95 °C without denaturing the Thermus aquaticus (‘Taq’) enzyme.

The ‘ingredients’ needed in PCR include a segment of the DNA strand to be analysed, free nucleotides containing the nitrogen bases adenine, thymine, guanine and cytosine, synthesised ‘primer’ sections of DNA (base sequences that occur on either side of the desired DNA strand), Taq polymerase and a primase enzyme that anneals the primer sequences to the unzipped DNA strands.

Billions of Copies of the Desired DNA Segment in Three Hours

The PCR process commences by heating the reaction mixture to 95°C. This denatures the DNA sample to form two separate strands. The temperature of the mixture is then reduced to 60°C, ideal conditions for the primer sequences to form hydrogen bonds with their complementary sections on the free DNA strands.

Fig. 2 - The PCR Process 

Following this step, the temperature is elevated to 72°C. This is the optimum temperature for the Taq polymerase enzyme, which sets about adding complementary nucleotides to the desired segments of the DNA strands until two new double stranded DNA copies of the original segment are formed. After 30 cycles of these steps (see figure 2), which take about 3 hours to complete, up to one billion copies of the required DNA segment can be produced.

Uses for PCR in Biotechnology

The polymerase chain reaction can be used in any instance where multiple copies of a desired DNA sequence are required for analysis. Examples of this include situations where minute DNA samples from blood, tissue or bodily fluid samples found at crime scenes need to be amplified for identification using electrophoretic separation techniques, or in archaeology where small amounts of mitochondrial DNA from bone fragments or teeth can be multiplied and examined.

Other uses for PCR include the diagnosis of diseases, where unknown pathogens can be identified from their DNA. Examples of diseases that have been diagnosed in this way include AIDS, Lyme disease, middle ear infection, tuberculosis, chlamydia infection and viral meningitis. PCR techniques are often more efficient than attempts to culture and identify the various microorganisms that cause these diseases.

PCR was also instrumental in the isolation and amplification of human genes during the Human Genome Project and is used in other gene sequencing procedures. In addition, PCR is being increasingly employed in recombinant DNA techniques as a means of producing multiple copies of transgenes – genes from one organism that are inserted into the genome of another. This method is proving to be more effective than cloning the desired gene in vectors such as bacterial plasmids, as the risk of mutations is reduced.

Recent Innovations in PCR Technology

Initially, DNA segments produced in PCR were identified using gel electrophoresis, but the advent of ‘real time PCR’ has obviated the need for this in some cases by using fluorescent probes or dyes which can be detected using optical sensors. Another improvement in PCR technology has been the development of PCR cycler machines which can automatically switch between the different temperatures required in the reaction. Prior to this the PCR tubes had to be manually moved between water baths which were set at different temperatures.

The polymerase chain reaction has been described as one of the most important scientific breakthroughs to have occurred in the last hundred years and, according to Tabitha Powledge, has ‘utterly transformed the life sciences’. It has effectively made DNA readily accessible in all areas of scientific research.

References

Bethseda, MD, 1992, ‘Polymerase Chain Reaction- Xeroxing DNA’, Access Excellence Resource Centre, accessexcellence.org, accessed 4/7/2010

Dolan DNA Learning Centre, ‘Polymerase Chain Reaction’, Biology Animation Library, dnalc.org, accessed 4/7/2010

Dolan DNA Learning Centre, 'Naming PCR', Biology Animation Library, dnalc.org

, accessed 4/7/2010

National Human Genome Research Institute, 2010, ‘Polymerase Chain Reaction, PCR’, Genome.gov, accessed 5/7/2010

Powledge, T. M, ‘the Polymerase Chain Reaction’, Breakthroughs in Bioscience, faseb.org, accessed 5/7/2010

Making Emulsions in the Classroom

Fig.1 - Water and Oil Don't Mix

Oil and water do not dissolve in each other, a phenomenon which can be observed if a mixture of the two is left to stand for a short amount of time (see figure 1). The oil, being less dense, floats on top of the water, forming an upper layer. Students can observe the difference between these two layers by adding a few drops of food colour to such an oil-water mixture. Because it is insoluble in oil but soluble in water, the food colour clings together as distinct drops as it moves through the oil layer and then dissolves to form an even colour when it reaches the water layer.

When such a mixture of oil and water is shaken, drops of oil are suspended evenly throughout the preparation for a while, but the original layers eventually re-form. The addition of substances known as emulsifiers can, however, maintain the stability of suspensions and prevent them from settling back into layers.

Making Hair Cream – Materials and Teaching Method

Fig. 2 - Hair Cream

In both creams and ointments, the emulsifying agent is often a type of detergent, which acts to stabilise the interface between the oil and water in the mixture. Detergents have molecules with both hydrophilic (water loving) and hydrophobic (water hating) components. This results in one side of the detergent molecule binding to water and the other side binding to the oil.

In this activity, an emulsion of water and paraffin oil will be stabilised using soap flakes as the emulsifying agent. Soap flakes can be obtained from several companies, including Dri-Pak and Lux, while paraffin oil can be purchased from some hardware stores. Students will produce a thick, white cream that can be used on the hair "Elvis-style," or used as a hand cream.

The following materials and equipment are required per group of around four students:

•                ½ teaspoon soap flakes

•                10 ml hot water

•                30 ml paraffin oil

•                Plastic cup

•                Teaspoon or stirring rod

Students should be instructed to copy down the following directions, which should be followed by a teacher-led explanation.

1.             Mix the soap flakes with the hot water in a plastic cup. Stir until the soap has dissolved.

2.             Add the paraffin oil, stirring continuously.

3.             Keep stirring for the next 15 minutes or until the emulsion has completely cooled. By this time it should have formed into a thick, creamy, white mixture that resembles many commercially available preparations (see figure 2).

The following questions could be written on the board after students write up the experiment and their observations:

•                What is an emulsion?

•                Name the two liquids present in this emulsion.

•                Explain why the soap flakes act as an emulsifying agent in this mixture.

Making Mayonnaise – Materials and Teaching Method

Fig. 3 - Mayonnaise

Mayonnaise is really salad dressing with egg yolk added as an emulsifying agent (see figure 3). The protein lecithin in the egg acts to maintain the stability of the oil and water suspension by coating the oil droplets so that they can’t settle out again into an upper layer. Note that technique is important in this activity: if the oil is added too quickly it will not be properly coated by the lecithin and curdling (separation of the oil and water) will result.

The following materials and equipment are required per group of approximately four students:

•                250 ml olive oil

•                1 egg yolk

•                1 lemon

•                A small amount of water

•                A pinch of salt and pepper

Students should be instructed to copy down the following directions, which should be followed by a teacher-led explanation.

1.             Use a whisk to mix together the egg, lemon, salt and pepper.

2.             Slowly whisk in the oil.

3.             The mixture should start to thicken. If it becomes too thick a small amount of additional water can be mixed in.

Using a whisk will help to aerate and add bulk to the mixture. Students should not be concerned if the mayonnaise is not as thick as commercial mayonnaise – this is the way it should be and is in fact the consistency preferred by many chefs.

The following questions could be written on the board after students write up the experiment and their observations:

•                Name the two liquids suspended evenly throughout the mayonnaise.

•                Which ingredient acts to emulsify these two liquids?

•                Why does the oil need to be added slowly when making mayonnaise?

Emulsions Follow-Up Activities

Students could research information on the use of other emulsions in the food and pharmaceutical industry and attempt to recognise that emulsions belong to a larger group of suspensions known as colloids, which include preparations where one of the two phases can be a solid. Colloids such as paint, for instance, can be made in the classroom using chalk powder, glue and water.

References

CSIRO, 2006. "An Oily Problem." (accessed 23/7/2010).

Lechner, A., "Soaps and Emulsions." St. Louis University School of Medicine. (accessed 20/7/2010).