22 minutes reading time (4303 words)

    Artificial Sweeteners

    Maureen Prince
    University of Canterbury

    By far the most commonly used sweetener is sucrose, usually referred to as sugar Awareness of health hazards associated with a high-sugar diet has not been sufficient to overcome the human predilection for sweetness. To ameliorate these health problems while allowing people to indulge their liking of sweet things (and at the same time making money) chemical companies have been searching for sugar alternatives - both 'artificial' and natural.

    Sugarβ-D-fructofuranosyl-α-D-glucopyranoside, saccharose or sucrose is a disaccharide of glucose and fructose. It is formed in plants by photosynthesis. In sugar cane it is the main storage carbohydrate but in many other plants it is converted to, and stored as, starch, inulin or levin. The transportation of oligosaccharides and polysaccharides in some plant species occurs by conversion to sucrose, translocation and then resynthesis. 

    The major source of sugar, accounting for two thirds of the 100 million tonnes of sugar produced annually, is sugar cane. A native of Polynesia, sugar cane was taken to China and then India, where it was first refined into sugar in about 700BC. Cultivation spread through Persia to Egypt and then to warmer parts of the Mediterranean by 800AD. The first sugar reached England in 1319 as an expensive novelty used mostly in medicines. Its use in Europe was limited and expensive until the seventeenth century, when imports from Caribbean plantations became readily available.

    During the Napoleonic wars, British naval blockades cut off French sugar supplies from the island of Dominica and French scientists set about the task of seeking an alternative source. They soon discovered that sugar could be extracted from root vegetables such as parsnip and, particularly, the sea beet. Selective cultivation led, within ten years, to the development of sugar beet, which, until last century, was the source of most of the world's sugar.

    Crystals of sucrose melt between 185 and 187°C (depending on solvent of crystallisation) and are water-soluble. It is a non-reducing sugar which is readily hydrolysed by acid but is stable to alkali, is heat stable and will keep indefinitely without need for refrigeration. It is relatively cheap to produce and is a good bulking agent. It is not, however, particularly sweet.

    Disadvantages of sugar
    The average weekly consumption of sugar in the western world is about 750 grams per person, mostly used to satisfy a craving for sweetness. This amount of sugar provides 12,500 kilojoules of energy (16.7 kJ/gram) but has no additional nutritional value.

    Following ingestion, sucrose is broken down into fructose and glucose. The latter is the body's main source of energy. It can be converted into glycogen, which is stored, in quantities of up to 350 grams, in the muscle and liver tissue. This amount of glycogen will provide approximately 1400 kilocalories, enough energy for one day's activity. Once these storage areas are full, any excess glucose is stored as fat.

    Peoples' desire for sweet foods leads to the overeating of sucrose, which, in the developed world, contributes to obesity and consequent ill health. Sucrose is also cariogenic - it is metabolised by plaque bacteria to form acids which attack calcium phosphate in the enamel surface of teeth.

    It is clearly in the interests of the people of the western world to reduce their sugar intake. But desire is strong and the will is weak - in affluent nations it is easier (and more acceptable) to find sugar substitutes than to modify dietary habit.

    Development of non-sugar sweeteners
    Sweeteners are classified as bulk or intense, nutritive or non-nutritive.

    Bulk sweeteners (including sucrose) are generally carbohydrates or derivatives extracted from plants and other natural sources. They can usually be metabolised to provide energy and are therefore nutritive. Since they are not particularly sweet they are used in large amounts to give the desired sweetness; hence they contribute to the bulk and structure of foods. They also contribute to osmotic, preservation, and bodying (or mouth feel) properties of the food, and they undergo the Malliard reaction, which gives food its brown colour after cooking.

    Intense sweeteners have a stronger taste and are needed in much smaller amounts. They are usually synthetic compounds and, in most cases, are non-nutritive, providing little if any energy.

    Many factors must be considered when developing a new sweetener. The compound should be water soluble, have a long shelf life and be stable to high temperatures and acidic conditions. Its taste profile should be similar to sugar - a quick sweetness followed by a sharp cut off and no aftertaste. The energy value should be low and the compound and its metabolites should be non-toxic and devoid of undesirable side effects, including the promotion of dental caries. Finally, production should be economical.

    Sweetness is determined by panels of people who taste increasingly dilute solutions of a compound in water until they can no longer perceive a sweet taste. The measure of sweetness is given relative to a sucrose solution, which is assigned a value of 1. A point to note is that relative sweetness tends to vary with concentration. For example the sodium salt of saccharin is 720 times sweeter than a two percent (by weight) sucrose solution, but is only 110 times sweeter than a ten-percent solution.

    Taste panels are also trained to look for certain taste qualities: appearance time (how long till the taste is apparent); extinction time (how long the taste lasts); and flavour profile, including aftertastes which might include, bitter, salty, metallic, cooling or liquorice characteristics.

    Because some sweet compounds are potentially harmful, they usually undergo mouse toxicity trials and bacterial mutagenicity tests before humans taste tests. Behavioural conditioned aversion tests are sometimes used in which the similarity of a compound to sucrose is determined by monitoring the amount of solution consumed by Mongolian gerbils trained to avoid sweet, salty, sour and bitter taste qualities. The reliability of this assay method was determined using known sweet compounds as controls.

    Many thousands of molecules elicit a sweet taste. The final choice of sweetener is influenced most strongly by the consumer. Public concern over artificial or synthetic food additives has seen an increasing attention devoted to sweeteners from 'natural origins'. But most of the alternatives currently in use are synthetic or 'artificial'.

    Intense synthetic sweeteners
    SapaThe first recorded artificial sweetener, discovered by the Romans and called sapa, was prepared by boiling grape juice, wine lees or soured wine in a lead pan to produce a sweet syrup. Wine contains acids such as tartaric and citric acid. If it also picks up spores of the common Acetobacter the alcohol is converted to acetic acid which is sour. When boiled, the acetic acid reacts with lead to produce lead acetate, a sweet but toxic compound that is also known as sugar of lead.

    Sapa was used to sweeten foods and also to 'improve' wines - it killed the bacteria that caused the wines to sour.(1) It was also popular amongst prostitutes because it gave them a pale complexion and had a contraceptive effect. The Romans were rightly suspicious of sapa. It was reported to make people tired and listless, anaemic, constipated and infertile, but it did taste nice.(2)

    The American scientist Ira Remsen and Russian-born Constantin Falhberg discovered saccharin (3-oxo-2,3-dihydro-1,2-benzisothiazole-1,1-dioxide) at the John Hopkins University in 1879, at a time when it was common practise to include taste in the characterisation of chemical compounds. Saccharin is about 300 times sweeter than sugar and is most commonly synthesised as a sodium or calcium salt. It has good stability in conditions prevalent in food preparation and has been used as a sweetener for about 80 years. For a time it was the only non-sugar sweetener available.

    Saccharin cannot be metabolised and is therefore non-nutritive. Its main use has been in weight-control and diabetic products, vitamin preparations and toothpaste, although many people find it has a metallic or bitter aftertaste. In terms of dental safety, saccharin is a very good sweetener. It exhibits a degree of inhibition of the microorganisms associated with dental caries and may also curb dental plaque formation.

    Since the discovery of bladder tumours in rats fed with high levels of saccharin, there has been a lot of debate over its safety. However, numerous studies and expert committees have concluded that it is safe for humans even in very high doses.

    Saccharin is currently used in more than ninety countries, often in a blend with other sweeteners to give a synergic sweetening effect. For example, a ten-to-one mixture of saccharin with cyclamate gives a product that is sweeter than either in their pure forms.



    Cyclamate, or cyclohexal sulfamate, was discovered in 1937 by Michael Sveda at E.I. DuPont de Nemours. On placing his cigarette on the laboratory bench (a practice that would be highly frowned upon today) he accidentally contaminated it with the compound he was working on. When he next took a drag he experienced a sweet taste.

    Cyclamate is available in its acid form or as a sodium or calcium salt. It is thirty times sweeter than sugar, but only a tenth as sweet as other artificial sweeteners and so quite large quantities are required. Its taste profile has a slow onset and is quite persistent. It is stable to temperature and sufficiently soluble for use in drinks and as a tabletop sweetener.

    In the mid 1960s cyclamate dominated the market for artificial sweeteners. In 1970 it was banned in some countries after a high incidence of bladder cancer was found in rats fed a blend of cyclamate and saccharin - even though those doses corresponded to the consumption by humans of 800 cans of soft drink a day.

    Cyclamate is metabolised only by a very small population of people, its major metabolite being cyclohexylamine. Tests on the compound and its metabolites have failed to show potential for carcinogenicity. It has synergistic effects with other sweeteners and is widely used in low-calorie foods and drinks. 


    Acesulfam K

    Acesulfam K is the common name for 6-methyl-1,2,3-oxathiazine-4(3H)-one-2.2- dioxide, which is sold under the trade name Sunnett. It was discovered, once again by chance, by Karl Claus of Hoechst who licked his fingers to pick up a piece of weighing paper. It is chemically similar to saccharin but has an improved aftertaste and is approximately 200 times sweeter than sugar.Acesulfam K is stable in water, acidic conditions and to high temperatures. It is not metabolised by the body and has shown no adverse side effects. Unfortunately its taste profile includes a bitter note. Acesulfam K is used in some foods, soft drinks, toothpastes, mouthwashes and pharmaceuticals.

    Acesulfam K


    (1,6-dichloro-dideoxy-b-fructofuranosyl-4-chloro-a-D-galactopyranoside) is a chlorinated derivative of sucrose. The sweetness of this and other sucrose chloride derivatives was discovered by Shashikant Phadnis who, when asked by a sugar company for samples to 'test', thought that they said 'taste' and tried them himself.

    Derivatives have been made with chlorine atoms replacing various hydroxyl groups in the sucrose molecule. The sweetest, with chlorine atoms at the 4,1' ,4'and 6' positions, is 2000 times sweeter than sucrose. The product with chlorine atoms at the 2,6,1', and 6'positions is extremely bitter. The derivative with chlorine atoms on the positions 4,1' and 6' is 650 time sweeter than sucrose. Although less sweet than the tetrachloro derivative, this trichlorogalactosucrose molecule is easier to make, and is used as a sweetening agent under the trade name Sucralose.(3)

    Sucralose is not metabolised and is therefore non-nutritive. It is crystalline, water soluble and stable to high temperatures and acidic conditions, but is very slowly hydrolysed to monosaccharide units. Its taste profile is very similar to sucrose and it has no bitter aftertaste. Having passed all necessary safety tests, Sucralose is currently approved for use in Canada, Australia, Mexico, Russia and Romania.



    The sweetness of aspartame was discovered in 1965 by James Schlatter who was working on anti-ulcer drugs for the company G.D. Searle and Company of Stoke, Illinois. About 200 times sweeter than sugar, it is known for its good taste profile and flavour enhancing qualities. It is sold in about fifty countries around the world under the trade names Canderel and Equal but is best known by the brand name NutraSweet, which is actually an aspartame-saccharin blend.


     Aspartame is a dipeptide of the amino acids, L-phenylalanine-1-methyl ester and L- aspartic acid. It is metabolised like any other protein and is therefore nutritive, but because so little is actually required its energy contribution is negligible. The presence of phenylalanine makes aspartame a potential health hazard for people who suffer from phenylketonuria, an absence of the enzyme that metabolises phenylalanine. Other drawbacks include its low solubility and instability in aqueous, acid and high-temperature conditions, which make it unsuitable as a sweetener in cooked foods. Aspartame decomposes at a rate of ten percent a month at room temperature, which limits its use to foods with a high turnover, such as soft drinks and fruit yoghurts.

    Aspartame is a poor nitrogen source for dental microorganisms and inhibits their growth and metabolism. This positive dental attribute is best when aspartame is used in combination with saccharin.

    Aspartame was first approved for use in 1974, then banned in 1975 before being reinstated again in 1981. Today it accounts for more than seventy-five percent of complaints about adverse food-additive effects to the United States Food and Drug Agency. Rather than aspartame per se, it is probably the metabolites aspartate, phenylalanine, methanol and diketopiperazine, that are responsible for these problems: headaches, dizziness, seizures, nausea, numbness, muscle spasms, joint pains, rashes, depression, fatigue, irritability, tachycardia, insomnia, vision problems, hearing loss, heart palpitations, breathing difficulties, anxiety attacks, slurred speech. loss of taste, tinnitus, vertigo, memory loss and weight gain.(4)

    Aspartic acid, phenylalanine


    Aspartame's main rival is the amino-acid-based sweetener alitame (L-a-aspartyl-N- (2,2,4,4,-tetramethyl-3-thietanyl)-D-alaninamide), developed by Pfizer Central Research. During its development, careful consideration was given to the effect of substituents on stability, sweetness and flavour attributes. The final compound is by no means the sweetest of its type but was chosen due to its synthetic accessibility. It is 2000 times sweeter than sugar and ten times sweeter than aspartame.Alitame has been shown to be safe up to 200 times the estimated chronic intake of 0.34mg/kg of body weight. It is a crystalline odourless non-hydroscopic compound of good solubility. It has a good thermal stability and shelf life, although the flavour diminishes with prolonged storage in acidic media due to hydrolysis. The aspartic acid component is metabolised, while the alanine amide metabolite generally passes through the body unchanged.


    Aspartyl - diaminoalkanes

    This new class of compounds involves modification of L-aspartyl-D-alanine amides where the terminal amide group is converted to an amine using phenyl iodosyl bis(trifluoracetate).

    Scheme and tetramethylcyclopentyl derivative

     Of a series of compounds synthesised, the tetramethylcyclopentyl derivative (I) is 600 to 800 times sweeter than sugar but with a similar taste. These new sweeteners are very stable to hydrolysis.

    Intense natural sweeteners
    Although sweet compounds may feasibly be present in microorganisms, marine organisms and lower order plants, all naturally occurring sweeteners discovered to date have been derived from higher order plant species. 75 plant constituents are known to be sweet. They represent 20 different structural types of compounds including sesquiterpenes, triterpene glycosides, dihydroflavonols and proanthocyanidins.

    There are more than 180 species of the Stevia plant but S. rebaudiana is the sweetest. Natives of Paraguay and Brazil have used the leaves of Stevia as a sweetening essence for centuries. Traditional uses include flavouring agents, herbal teas and medicines Eight sweet entkaurene glycosides have been identified from the leaves of Stevia, the principal one being Stevioside.

    Stevioside has been found in quantities of up to 10% (by weight) and is extracted as a white crystalline hygroscopic powder that is 300 times sweeter than sucrose. It has a slow latent sweetness, but also a strong bitterness and an unpleasant aftertaste. The bitterness is reduced in the presence of sugars such as sucrose, glucose or fructose. Stevioside is stable up to 95°C and so is suitable for use in cooked foods, but it is not very soluble in water. It is also non-calorific, non-fermentable and doesn't undergo any Malliard-type reactions.

    Rebaudinoside A is the next largest constituent of the stevia leaf and has a sweetness 400 times that of sucrose. Unlike Stevioside, it is very soluble in water, but it too has a bitter after taste (though not as bad as Stevioside). Due to its more desirable properties, Rebaudinoside A has been chosen for development on a commercial scale in Japan. To minimise the bitterness of the compound new extraction methods and different strains of the plant have also been developed.

    The best tasting Stevia plant is grown in Paraguay where the climate is most suitable Other varieties have a more intense bitter component and what is described as a grassy taste. Bitter tasting compounds are found to have the greatest concentration in the veins of the leaf while the sweet material is concentrated between the veins. Stevia has been used as a sweetening agent in Japan, China, Korea, Taiwan. Israel, Uruguay, Brazil and Paraguay for many years. Both Stevioside and Rebaudinoside A are commonly used in Japan for soft drinks, soy sauce, pickled vegetables and confectionery.

    Stevia has also been used as an antimicrobial agent, a digestive tonic and as a treatment for diabetes, cardiovascular complaints and skin problems. There have been no reports of ill health due to stevia in its 11,500 years of use. All safety tests of Rebaudinoside A and its metabolites have shown it to be safe for human consumption. Stevioside is not metabolised as its structure is very resistant to acidic and enzymatic cleavage. All toxicity tests have proven it quite safe. However, a metabolite of Stevioside, steviol, which is thought to be toxic, has been formed in the mecum of rats fed Stevioside, and both Stevioside and Rebaudinoside A can be metabolised to aglycone, a mutagenic, when fed to rats. Nevertheless, at present it has not been shown that this metabolism occurs in humans.

    Stevioside, Rebaudinoside A

    Neohesperidin dihydrochalcone (NHDC)

    This sweetener is synthesised by hydrogenation of Neohesperidin, which is a naturally occurring flavonoid found in citrus peel. NHDC is several hundreds of times sweeter than sugar with no bitter aftertaste. Its sweetness is relatively long lasting so it is normally combined with other sweeteners. It is also relatively stable over a wide range of temperatures and acidity conditions. In its pure form NHDC produces bitter, liquorice and cooling sensations. NHDC is mostly metabolised, although a small percentage can be excreted unchanged.This compound has currently been approved for use in Belgium and Argentina, mainly in soft drinks.

    NHDC - R = β-glcA2-β-glcA


    Hernandulcin is a sweet sesqiterpene found in the leaves and flowers of the plant Lippa dulcis. It has been prepared chemically as a racemate, but its isomer epihernandulcin is tasteless. Unfortunately in spite of its intense sweetness, Hernandulcin has a bitter aftertaste that makes it unsuitable as a sugar substitute. It is hoped that chemical alterations will enable removal of the bitter functionality.



    This compound is a triterpenoidsaponin found in the roots of the licorice plant. It is 50 - 100 times sweeter than sucrose and, not surprisingly, has a definite liquorice taste, Glycyrrhizin can be hydrolysed in the intestine to release a sugar moiety, glucuronic acid, that can then bind plasma proteins and enter with them into the enterohepatic system and be completely metabolised.

    Glycyrrhizin has many pharmacological properties including anti-viral, anti-ulcer, anti- inflammatory and anti-spasmodic activity. It has corticoid action by influencing steroid metabolism and it maintains blood pressure and volume. It is also involved in regulation of the glucose/glycogen balance. Glycyrrhizin is thought to be non-carcinogenic and its medicinal properties give it a variety of oral applications, other than a sweetener. The ammoniated salt of glycyrrhizin acid is available as a flavouring agent and a surfactant, although the latter applications are limited due to its taste.

    Glycyrrhizin - R = β-glc2-α-rha


    Thaumatin is a naturally occurring, liquorice tasting protein that comes from the fruit of a West African plant ketemfe, (Ihaumatococcus daniellii) and has the trade name Talin. It is a large polypeptide consisting of two separate but related proteins with a total molecular mass of 20kD. Although it is 3000 times sweeter than sugar - much sweeter than most artificial sweeteners, the onset of the sweet taste is slow. Unfortunately, the polymer structure of Thaumatin limits its use as a sweetener. It has many recognised sweet-receptor binding sites, so it clings to the tongue and its taste has a lingering effect. This characteristic is good for products such as chewing gum but prevents its use in many foods. Thaumatin is predominantly used as an additive to pet foods, but is permitted in some countries as a flavour enhancer for use in toothpastes and mouthwashes. Widespread use of Thaumatin has been undermined by its high price, but this may be overcome soon as the gene responsible for its production has been introduced to microorganisms in the hope that it can be produced more efficiently. Because Thaumatin is a naturally occurring polypeptide it doesn't have any toxicological problems and has been found to be safe for consumption in quantities 80,000 times greater than the expected levels of intake.

    Thaumatin - "Thaumatin I 1RQW" by Fvasconcellos 15:12, 27 November 2007 (UTC) - From PDB entry 1RQW.. Licensed under Public Domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Thaumatin_I_1RQW.png#mediaviewer/File:Thaumatin_I_1RQW.png


    Monellin is a sweet protein from the serendipity berry (dioscoreophyllum cumminsii). It is 3000 times as sweet as sucrose and has a molecular weight of 11.5kD. It is comprised of two amino acid chains, neither of which, by itself, tastes sweet. The sweetness of Monellin is destroyed when the protein is denatured; in hot or acidic environments.

    Monellin - "Hmonellin" by Pymol Image. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Hmonellin.png#mediaviewer/File:Hmonellin.png

     Although Thaumatin and Monellin are both intensely sweet proteins, they possess very few sequence similarities. They do however both contain five pairs of homologous triplets. It is thought that a combination of two or three of these sites may be responsible for the observation that antibodies raised against Thaumatin cross react and compete for Monellin as well as other sweet tasting compounds.

    Some advantages of these two proteins over other artificial sweeteners are:

    • Although nutritive they are low in calories due to their high potency.
    • They are safe and natural.
    • The genes that code for these proteins could be cloned in order to mass-produce the proteins.
    • The amino-acid sequence in the proteins could readily be modified to enable variations that give more desirable taste or physical properties.
    • The sweet genes could feasibly be cloned into plants, fruits or microorganisms.
    • Due to their high potency proteins could be used to isolate the sweet receptor(s).

    Miraculin is a glycoprotein isolated from the miracle fruit (richadella dulcifica) with a molecular weight of 42kD. The protein itself is tasteless but when added to a sour tasting compound it can result in a taste 400,000 times sweeter than sucrose that may last for over 24 hours! It is heat labile but inactivated in acidic conditions.Synergic sweeteningThe desirable properties of a sweetener may be achieved by blending together a selection of sweeteners with a variety of structures and metabolic pathways. One advantage of this approach is that the amount of each sweetener used may be kept well below the level at which doubts exist about its safety. It has been shown that a synergistic advantage may exist in binary or ternary mixtures. That is, the combination of two or three compounds can result in a mixture that is sweeter than any of the individual components. The sweetest mixtures occur when a bulk sweetener is combined with an intense sweetener. In these cases the advantages found in both types of sweetener complement each other, while any negative features are markedly reduced.


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    3. Life with Stevia: How sweet it is! Nutritional and Medicinal uses. Daniel Mowrey Ph.D.
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    About the author
    Maureen was born and educated on the Kapiti Coast of New Zealand, before moving to Christchurch to complete her undergraduate degree at the University of Canterbury. She is currently studying towards a Ph.D in chemistry.

    Part of the article is reprinted from Chem NZ No. 74 February 1999 pp 13-18

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