A Life in the Bubble

They welcome you to Christmas parties and pop their way in the New Year: the bubbles. They rise, dance and burst with the most style in Champagne, the golden socialite in the family of wines. Once again during the holiday, thousands, hundreds of thousands of pops will sound as bottles get uncorked over the world. The famous sparkling wine was born when the wineries of the Champagne region endeavoured to compete with the neighbouring duchy of Burgundy. To balance the acidity and lightness of their wines, they added yeast and sugar to the bottles after the initial fermentation. As the bottles are sealed during this second fermentation, the CO₂ produced stay in solution in the wine. Also, the starving yeasts cannibalize their own cell walls in the last phases of the process, releasing additional molecules. The bottles are kept upside down so that the lees fall in the neck, to be eventually. According to local tradition, the monk Dom Perignon developed the process, although it has been described some years before by a C. Merrett in the Royal Society’s proceedings. Ironically, Perignon had been hired in the first place to work on the wine production and reduce the Champagne wines’ effervescence, seen as a defect at the time. The pressure from the gas wrecked havoc in the cellars, causing the bottles to explode over time. Bubbles lovers can be happy that, if he did set new rules for the production of the Champagne wines, he was never able to eliminate its fizz.

Champagne grew to be seen as an affordable luxury, the drink of celebration for the upper and middle classes, thanks to a clever publicity effort. The label is strictly regulated: obviously, only wines form the region, produced according to the traditional méthode champenoise can bear it. Moreover, only nine historical varieties of grapes are allowed for the production, but only three are commonly used: Chardonnay, Pinot Noir and Pinot Meunier.

In the end, it is its bubbles that crown champagne king of festivities. What seems a simple empty sphere in the liquid hides a surprising complexity. Suddenly free from its glass prison, the gas escapes by any air/liquid interface available. At the bottleneck, the adiabatic gas release causes a sudden and noticeable drop of temperature: try noticing the cloud of condensed humidity next time you pop a bottle open. In the liquid’s body, the slightest air pocket can serve as a nucleation site for the CO2 to accumulate. Once a critical amount of CO₂ is attained in the pocket, a bubble breaks free and rise to the surface, leaving a vacuum behind that again, quickly get filled, starting a new cycle. If any fibber left from a dishcloth, any dust spec in the glass can serve as a nucleation site, some glass manufacturers engrave a pattern at the bottom of the flute to enhance the production of bubbles.

Born on a spec or in an engraving, the bubbles begin their lives of travel. Their mass movement creates an important convection effect in the glass. How the liquid is mixed by its bubble depends in the end of the glass’ shape. Flutes are more thoroughly agitated than coupes, affecting the outgassing process and creating different convection fluxes of the aromas. Bubbles can thus cause different “taste profiles” of a champagne served in different glass shapes. As it rises on its life’s journey, the bubble keeps growing. Given a champagne of typical density, the ideal gas constant, an average temperature of service of champagne and the expected pressure inside the bubble, a champagne bubble will expand at a rate of 430 mm/s (comparatively to 150 mm/s for a beer bubble). Some chemists specialized in champagne physic-chemistry – yes, such people exist – the final average size of a champagne bubble is expressed as

R ≈ 2.7 · 10^-3 · q^5/9 · (1/(r · g))^2/9 · (((c_L – k_H) · P₀)/P₀)^1/3 · h^1/3

Assuming the diffusion coefficient obtained by the Stokes-Einstein equation, and where q is the liquid’s temperature, r, the liquid’s density, g, the gravitational acceleration, c_L, the CO₂ content, k_H, Henry’s law constant, P₀, the ambient pressure and h is the distance traveled. In other words, the bubbles will tend to be larger when you start drinking, as there is more CO₂ in solution. On the other hand, the heat from your hand might compensate to a certain extent the effect. The glass will also affect the bubble sizes, as bubbles have a longer trajectory on average in the higher flutes. If you were to drink you champagne on the moon or on Mars, the bubbles would also be larger...

After their birth at the frontier of water and air and their journey through an amber world the bubbles arrive at their cemetery: the surface. A bubble will survive for a time assembled in rafts of up to six members, expanding slowly to an approximate critical radius of 100 nm, surviving then for a time varying between 10 and 100 ms. The life of a bubble might be short, but they go with a swan song. As they burst out of existence, their envelope of liquid is projected in the air. This envelope was enriched in surfactant molecule. The aerosols over the glass are thus enriched as well. It has been shown by mass spectrometry of champagne’s headspace contains ethyl esters of fatty acid such a myristoleic, palmitoleic, and oleic acids, that not only contributes to the aroma of a wine but also to its foaming capacity. Notably, the decanoic and dodecanoic acid esters can be enriched, giving respectively toasty and dry aromas. Higher concentrations of norisoprenoids have also been noted in the aerosols, these being responsible of notable fruity aromas. Bubbles are thus not only part of the ‘tactile’ experience of champagne, nor simple mixing agents, they create an entire experience for the taster before the liquid even touches its lips.

Beware of the consequence of champagne though: some lightweights say that sparkling wines make then tipsy faster: the CO₂ somehow enhancing the effect of ethanol. Although a study attempted to address the question (Roberts, 2007), the jury is still out. The presence of CO₂ in the ethanol solutions only amplified individual variations in alcohol absorption. But driven by the hypothetical synergy of CO₂ and C₂H₅OH or not, be careful when you pop open the bottle. As A Galloway notes in an article in the Lancet. “Champagne-cork injury to the eye” (yes, that is the actual title), the cork can easily attain speeds of 15 m/s, reaching the eye in a hundred us (an average blink takes 300-400 us). Another article (“Bottle cork injury and cap injury to the eye”) underlines in the most serious tone that “Bottle cork injury of the eye can cause severe damage to the globe with secondary loss of visual function that can be permanent as we observed in the literature and in the series we report. The dangerous effect of pressurized fluid, even under normal circumstances, is well known, as shown in various studies.”

Further reading :

Aguie-Beghin V. Adriansen Y. Peron N. Valade M. Rouxhet P. Douillard R., 2009, Structure and Chemical Composition of Layers Adsorbed at Interfaces with Champagne, J. Agric. Food Chem. 57, 10399–407

Archer D, Galloway NR 1967, Champagne-cork injury to the eye. Lancet 2, 487–9

Cavallini G.M., Martini A. Campi L., Forlini M. 2009, Bottle cork and cap injury to the eye: a review of 34 cases, Graefes Arch Clin Exp Ophthalmol, 247, 445-50

Gallart M. Lopez-Tamanes E. Suberbiola G. Buxaderas S. 2002, Influence of Fatty Acids on Wine Foaming, J. Agric. Food Chem., 50, 7042-5

Liger-Belair G. , Polidorib G., Jeandet P. 2008, Recent advances in the science of champagne bubbles, Chem. Soc. Rev., 37(11), 2490–511

Liger-Belair G. Vuillaume S. Cilindre C. Polidori G. Jeandet P. 2009, CO2 Volume Fluxes Outgassing from Champagne Glasses in Tasting Conditions: Flute versus Coupe, J. Agric. Food Chem. 57, 4939-47

Liger-Belair G. Cilindrea C. Gougeon R. Lucioc M. Gebefu I. Jeandet P. Schmitt-Kopplinc P. 2009, Unraveling different chemical fingerprints between a champagne wine and its aerosols, Proc. Natl. Aca. Sci. 106 (39), 16545–9

Roberts C. Robinson S.P. 2007, Alcohol concentration and carbonation of drinks: The Effect On Blood Alcohol Levels, J. Forens. Leg. Med., 14, 398–405

A Green Fairy Tale

"After the first glass, you see things as you wish they were. After the second, you see them as they are not. Finally, you see things as they really are, which is the most horrible thing in the world" – Oscar Wilde

Van Gogh, Gauguin, Wilde, Baudelaire, De Musset… At the beginning of the century, the greatest artists joined workers, clerks and businessmen to indulge in the ritual of absinthe. The liquor’s origin can be traced back to Antiquity, when oil of wormwood (Artemisia absinthium) was used as medicine. Eventually, the elixir, mixed with other herbs extract and eau-de-vie found its way as a popular liquor in 19th century Europe, sold as a 85% ethanol mix. Water was slowly dripped in the green alcohol over a cube on a pierced spoon. A white have (a spontaneous emulsion of anisol) would appear, familiar to drinkers of pastis, ouzo and raki, and the absinthe was ready to be savoured. It became a fashion, then a rage and finally a phenomena. It even became a character, both in ads and tour de siècle culture : the Green Fairy. Workers and artists alike were indulging in the ritual every day - too often many times a day. For the firsts the absinthe ritual was their moment of peace, the seconds venerated absinthe as a muse, like 70s’ artists would later see LSD. Absinthe was not without its detractors. It was accused of causing “absinthism” : a mixture of hallucinations, convulsions, depression, insomnia and paralysis. Notably, Magnan, a French physician, isolated thujone as the active ingredient of absinthe, causing convulsions in rats. This was the final hour of absinthe. Political activists and prohibitionists began petitioning for a ban. At the beginning of World War I, absinthe was the cheapest strong liquor a soldier could buy. Frightened by the claims of the prohibitionists and hoping to stop the havoc of alcoholism among the troops virtually every country banned absinthe.
A legend was born : The Green Fairy, offering madness in a bottle.
In recent years however, unlikely shiny-armoured knights rode to rescue the disgraced lady. Biochemists took up the case and investigated thujone again, as absinthe from Eastern Europe was seen more often and distillers were pushing for a lift on the ban. Severe flaws were found in Magnan’s research. As a prohibitionists himself he was severely biased against absinthe and refused to distinguish between the symptoms of “absinthism’ and alcoholism. He also injected rats with quantities of thujone nowhere near the levels found in actual absinthe. Even then, chromatographic analysis on vintage absinthe and freshly prepared beverages showed concentrations of thujone of 25mg/l, far from the 260 mg/l reported in older studies.
Even if thujone was the deadly poison presented by the politicized scientists of the 10s, the levels present in absinthe were thus harmless.
Moreover, this toxicity has been reassessed today. Based on its structure and on its reported stimulating effect on artistic abilities, thujone has been investigated as a possible cannabinnoid, akin to THC. It was showed that it indeed binds to the CB1 and CB2 cannabinnoid receptor with it is only with a low affinity (Ki > 100uM). It does not however - nor does any component of oil of wormwood – affect the coupled G-protein or adenylate cyclase activity in a cannabinnoid-like fashion. Absinthe was then cleared as a psychedelic drug. It has been confirmed in high dosage as a convulsant though, acting as an antagonistic inhibitor of GABAA receptors. Thujone has also been shown to inhibit indirectly the 5-HT3 receptors present in the serotoninergic pathways, acting as an enhancer for natural agonists of the receptor. The effect on GABAA and 5HT3 receptors can explain the stimulating effects reported by absinthe drinkers and the convulsant properties of very high doses of a-thujone. Common alcoholism and the presence of copper and antimony salt as well as methanol on cheap absinthe would rather explain the reported cases of absinthism, although it remains to be demonstrated.
Biochemists of today, thus stood above the example of the biased researchers of the past, too often attached to political causes. The return of the Green Fairy liquor store’s shelves does not sound a new vague of madness, but rather an occasion to savour a legendary and delicious aniseed drink! Cheers.

Further reading :
Lachenmeier D. W. et al., (2009), J. Agric. Food Chem.
Lachenmeier D. W. et al. (2006) Forens. Sci. Int. 158, 1-8
Del Castillo et al. (1975) Nature 253 356-65
Mescheler J. P. et al. (1999) Pharmaco. Bioch. and Behav., 62(3), 473–80
Deiml T. et al. (2004) Neuropharmacology 46, 192–201

Delicious Green Eggs : Intriguing Protein Gels

Would you prefer your eggs sunny side up or easy over? Scrambled, maybe? However, there is something to say for a nice century egg, a pidan, and its hearty flavour, cheese aroma, its translucent and tea-colored “white” and bold green yolk. This Asian delicacy is prepared following a time consuming process. Duck eggs are wrapped in ash, salt, quicklime (a mixture of calcium carbonate and oxide) and, sometimes, tea and left to rest for a hundred days Lead oxide can be added to speed up the maceration; the gourmet minding his mental health and hand-eye coordination can substitute it for zinc oxide. The resulting product can be preserved for weeks, the ‘century’ of its name being a slight hyperbole of its resilience.
Since 1916, chemists attempted to understand the science behind the transformation. They found that the alkalinity of the solution is the main agent of transformation along with divalent cations, helped by the occasional Bacillus cereus and macerans, the eggs emerge in their famed appearance. From 9, the pH of the white can climbs to as high as 13 and the pH of the yolk, from 6.5 to 9. Apart from proteolysis, dehydration of the white and degradation of the yolk’s lecithin, such pH jumps also allows for racemisation of amino acids and an intricate unfolding process of the ovalbumin : egg white’s most abundant protein.
Pidan attracted the attention of gel specialists. Researchers at Cambridge observed that the ovalbumin aggregates in a particular way under the action of alkali. Most of the research on proteins colloids has focused on amyloids fibrils: denatured proteins, which, regardless of their sequence, assemble in long b-strands (Alzheimer’s disease is a famous example). The firmness of the century eggs comes be from more obscure structure. Under the slow action of extreme pH, the ovalbumin unfolds only partly. The denatured strands of proteins coagulate, forming fine chains between still-folded cores. The later are strongly ionized and kept away from one another by electrostatic repulsion. The resulting structure creates an intricate pattern of fine strands and ordered cores that are resistant even to boiling water. The pattern is uncommon in nature, but some believe it could shed light on the assembly of protein folds, opening the door on new horizons of biochemistry. As of what the traditions of the East can inspire even Cambridge’s biophysicists...

Further reading
Blunt K. et al., J. Biol. Chem (1916), 28, 125-34
Wang J. et al., Crit. Rev. Microbiol. (1996), 22, 101–38
Eiser E. et al., Soft Matter, (2009), ), 5, 2725-30

Fresh and Fragile Pilsner

On a restaurant’s patio or a friend’s balcony, it is time to enjoy the summer, the sun, the barbecues, with a fresh beer at hand… and no is more fresh than the pilsner.

Born in Bohemia during the 18th century, it was among the first blonde lagers. The family encompass the beers produced by bottom-fermenting. The process involves the fermentation of the mash by Sacharromyces uvarum at around 10°C in wide, shallow vats. The yeasts flocculate at the bottom of the vats, hence the name. The low temperature allows only a relatively low alcohol yield, while the short path of the CO2 bubbles produced in the vats prevents it from “fishing” out the aromatic compounds on its way up.
The resulting golden product was a huge success. Pilsners benefitted from the replacement of metal and clay mugs by clear glasses. For the first time, customers were able to see what they were drinking. Appearances in this case were not deceiving. Pilsner is defined by its crisp and fresh taste, granted by the strong aromas of hops and malt: the perfect bittersweet beer. Sadly, its flavour is as fragile as it is delectable.
Notes of skunk and cardboard can quickly deteriorate the balance of pilsners. How does this phenomenon can take place in a closed bottle? Beer is 95% water, 5-ish% ethanol, the rest being sugars and other various organic compounds creating the aroma and taste of the product. For the pilsner, many of these compounds come from the high amounts of hops added in the brewing. In recent years, it has been shown that at least 40 organic acids and furanones were responsible for the pilsner’s aroma and that a mix of 23 molecules was necessary to approximate it artificially.
Pilsner, with their high hop content are especially prone to develop a skunk odour... but only when they are stored in clear bottles. Light excites the beer’s aromatic compounds, which in turn react with specific isomers of organic acids derived from hop. Add a little sulphur compounds in the mix and the skunky 3-methylbut-2-ene-1-thiol is produced. Pilsner lovers learn quickly to beware of clear bottles and to go for cask or cans.
But the lager’s skunk odour is not the only danger for the pilsner it is also prone to develop during storage a strange “off’ taste. Recently, it has been shown that a class of compound, a-dicarbonyls, are steadily produced by the enolization of carbohydrates. There was no surprise there: Sacharromyces is one of the most creative chemist and new compounds are discovered everyday in alcohols.

The real interest came with the realization that the a-dicarbonyls were degraded in aldehydes and enols in a Maillard reaction. These reactions take place usually at high temperatures between a reducing sugar and an amino acid or a peptide, producing tasty, brownish products. We have to thank it for the bread’s crust, caramel and roasted coffee. In a Pilsner bottle though, the Maillard reaction to happen (although quite slowly), and produces... the unwanted flavours of expired beer. The next step for the industry would now consist of inhibiting the final step. Sulphites, by examples have this ability, albeit they are not popular among the public, without real ground... But that would be the subject of another column...

For further reading :
Bravo et al. J. Agric. Food Chem. (2008) 56(11), 4134-44
Fritsch et al. J. Agric. Food Chem. (2005) 53(19), 7544-51
Jaskula et al. J. Agric. Food Chem. (2008) 56(15), 6408-15

Get That Brain Sweating With Some Sport Drink

Feeling guilty about your sweet tooth? Don't : it could help you getting better at sports.
If sugar means energy, sweet drinks should not boost your performance if you exercise for less than an hour. The organism simply cannot process carbohydrates that fast... However, studies did shown that drinking the sugary sport drinks enhance performance... but only if they are drank; not if they are injected (even if publicists would love the picture of an athlete with a Gatorade I.V.).
Recent experiments involving brain fMRIs of cyclists were able to reconcile the mysterious power of sports drink with the basic principles of biochemistry. Athletes drinking saccharin – a sugar substitute - show activity in their operculum and DLPFC. If they drink glucose-laden water tough, regions in their striatum and cingular cortex light up as well. At the same time, the performance of these cyclists drinking one of the two last solutions was improved by 2 to 3 %.
It is already known that the striatum and cingular cortez are involved in reward mechanism, affecting the dopaminergic pathways. On the other hand, the power output of athletes during exercise can be lowered by the pain and aches developing through their body. A model now advanced by the research group is that activation of certain regions of the brain by carbohydrates might help bypass this effect.
Sport drinks work: doesn’t she look energized?A remarkable observation is that the same effect is observed for a non-sweetening carbohydrate – maltodextrin, as well as for glucose. Protein receptors of the sweet-tooth, T1R2 and T1R3, thus seem involve3d and that process. Another, “secret” type of receptor might be hiding in our mouth, ready to detect the presence of energy at the tip of your tongue...

For further reading
Chambers et al., J. Physiol. 2009, 1779-94

The amazing scientifically optimized pizza

Pizza is arguably the perfect food. It can be adapted to all tastes, contains the whole array of food groups, is visually apetizing, simple to eat and… well simply delicious. Born in the 18th century poor houses of Naples when they decided to add some of those cheap and overlooked tomatoes to their flat bread, the pizza was complete when their countrymen added for flavour oil, anchovies, basil or mozarella.
The later can be seen as one of the finest addition. Coincidence or culinary genius of the enlightened Italy, mozarella is the perfect physico-chemical companion to pizza. Cheese in essence a gel made of two intermingled phases : the solid curds and the liquid whey – a eutectic mixture. At room tempreature, the mix is stable, but heat it up and eventually the two phases will separate and never form back a gel even if cooled. The eutectic characteristics of mozarella allow it to melt across just the right range of temperature without burning, nor causing its separation in its two constituants.
If the cheese is the crown of the pizza, its foundation and secret weapon is its crust. Not only must it be soft, light and hearthy, the stylish crust has to be shaped in the air with the famed italian’s chef toss. The trick makes the gourmand Napolitans drool and the mechanical engineers of Monash University think. They observed that the tossing of the pizza dough mimic the motion of their ultrasonic motor. In the hope of optimizing it, they studied the tour de main of italian bakers while shaping the perfect pizza. They observed that the first toss has to be helical to maximize the energy transmitted by friction. However, to keep the pizza rotating at its maximal speed, the subsequent tosses should follow a tilted ellipse.
As a final note, if, minding your health and not your taste buds, you suffer from pizza guilt, researchers have also had a tought for you. Whole wheat crust sounds good to you? Many studies link the benefits of whole wheat with a highest antioxidant potential. Investigating the influence of the baking process on it, researchers observed that the longest you allow the dough to ferment and the slower you cook it, the higher the antioxidant potential of the crust will be.

For further reading
Liu KC et al., (2009) Europhys. Let., 85, 6000, 1-5
Moore J. et al. (2009) J. Agric. Food Chem., 57(3), 832-9
Cobb C. & Fetterolf ML, The Joy of Chemistry, Prometheus books, New York, 2005, ch. 14

You say tomato...

Red, round and plump : that is how we picture tomatoes. But its genome can give us a very different picture of many favourite fruit... or is it a vegetable?
Indeed, before its encounter with humans, in pre-Colombian America, the tomato was a simple reddish berry. When it came to berries, the ancient Meso - Americans, bigger seemed to have assumed that bigger was better. The domestication process that tomato underwent with them selected eventually two mutations in the fw2.2 and YABBY genes, both controlling the numbers of carpel – the parts of the flower that eventually develop in the compartments of the fruit. The effects were drastic as some domesticated tomatoes are now 1000 time larger than their wild ancestors. Try to picture the humans of 5000 years ago evolving into 50 tons giants along the ages...
But the gardeners of today are not as patients as before, nor as limited. Molecular biologists decided that the tomato could use a touch of... flower. Simple as that: they inserted two transgenes from a snapdragon in a tomato’s genome. Del and Ros1N created a tomato expressing a flower’s anthocyanins, powerful antioxidants, which also turns the tomato bright purple. Original, delicious, and healthy: who could ask for more?

For further reading :
Cong et al. 2008, Nature Gen., 40(6), 800-4
Butelli et al. 2008, Nature Biotech, 26(11), 1301-8

Foods to put us under pressure

In recent years, nitric oxide took the center stage in cell signalling, immunology and cardiovascular health. Far from being only a product of the NO synthases, it can come up through our food in unexpected ways.
When vegetables rich in nitrate are consumed, it will eventually make its way in our saliva, were bacteria will transform can transform it in nitrite and in nitric oxide it through a NO3- reductase complex. When NO enter our stomach, it triggers the production of a thicker layer of mucus. The beneficial effects of nitric oxide along the digestive tract do not even stop at the stomach. In the intestines, it can work as a mild oxidant in concert with acidity to control the levels of possibly pathogenic bacteria. This underlines a problem for us, hygienic North Americans: mouthwash products kill the nitrate reducing bacteria of the mouth. Halitosis or stomach ulcers... we are left with a difficult choice.
The food/NO connection can also present itself in funnier ways. Watermelon contains high levels of citrulline, the precursor for the biosynthesis of arginine. The aminoacid supply the NO synthesis pathway, allowing its levels to climb up in the blood. And higher levels of NO in the blood means... vasodilatation... While sildenafil affects the degradation of NO, watermelon by inhibiting PDE5 (cGMP specific phosphodiesterase type 5), watermelon could thus, in theory, mimics its effects on NO vascular concentration. On the downside, to observe the same influence on... localized blood flow, you would need 4 litres of watermelon. A single slice before going to bed would do little more than quench your thirst.

For further reading :
Petersson J et al, Am. J. Physiol. Gastrointest. Liver Physiol., 2007, 292,G718
Collins JK et al, Nutrition. 2007, 23(3), 261-6

Savoury proteins

Even if we take our senses for granted, they can still hide surprises. Eastern chefs discovered first, at the beginning of the century, that sweet, bitter, salty and sour are not the only tastes that our buds can perceive. We can enjoy a fifth side of flavour in our plates, the “savouriness”. The world now refers to it more and more as umami, the name given by its japanese discoverer. It comes especially from glutamate; and thus, from proteins-rich food: meats and their broths, algae, cheese, soy and mushrooms. Umami is the secret of oriental cuisine and its controversial condiment, MSG – monosodium glutamate – that gives our palates a hearty feeling.
A century after its first official description by professor Ikeda, Umami was still keeping secrets from the culinary scientist. An in it these lied one of its most wonderful potential for the adventurous cook : its taste can be multiplied exponentially by a variety of ingredients. Notably inoside and guanoside monophosphate, as well as certain sweeteners greatly enhance its flavour.
The umami taste receptor, mGluR4, presents an extensive similarity with the sweet taste receptor. Both are G-coupled heterodimeric protein complex and share a ligand-binding domain, TIR3, while the umami taste receptor possess a unique glutamate-binding domain, TIR1. The association of glutamate to TIR1 elicit the signal that our brain interprets as a hearty flavour. Interestingly, when conserved residues between TIR1 and TIR2 are mutated, the synergetic effect of IMP and GMP is lost. Using molecular modelling, chemists showed that the mystery resides in the phosphate group of the molecules. They allow IMP and GMP to bind near the entrance of the crevice to positively charged residues, stabilizing a closed conformation around the glutamate and thus stimulating the production of the signal to the brain.
A wonderful examples of molecules working together for our enjoyment!

For further reading :

Zhang F. et al. 2008 Molecular mechanism for the umami taste synergism Proc. Natl. Ac. Sci. 105(52), 20930-4

Flavors from the devil

My final, considered judgment is that the hardy bulb [garlic] blesses and ennobles everything it touches - with the possible exception of ice cream and pie.” Angelo Pellegrini, 'The Unprejudiced Palate' (1948)

Sulphur compounds do not only keep in check the reduction potential of our solutions in the lab: Nature brings them to our noses and palate as well, leaving their stamp on our cuisine. The pungent smell given by crushed garlic, the tears flowing while cutting onions and the aftertaste of Sauvignon Blanc all share their origins in them. In many foods, the potential of sulphur for redox chemistry makes it subject to the enzymatic transformation of its organic derivatives in flavorful components.
In the cells of the Alliaceae family (which include garlic, onion, shallot, and chive) the enzyme alliinase is sequestered from the cytoplasm. When a bulb of garlic (Allium sativum) is crushed or cut, the cells are damaged and alliinase is released in the cytoplasm. Once there, it comes in contact with alliin, a cysteine derivative without particular smell. Alliinase catalyze oxidize it to give allicin, which gives its… pungent... smell to garlic. Apparently, somewhere along its evolution, the Alliaceae family found the trick handy when animals decided to grab a bite at their expense.
This might help the resourceful biochemist cooking with garlic. For garlic with the flavor but without the bad breath, wrap your bulb in the aluminium foil with olive oil and put in the oven at 325 °F for an hour. The heat will easily inactivate the alliinase.
The alliinase released in onions has a different effect. It allows ultimately the formation of syn-propanethiol-S-oxide from sulfenic acid. The molecule is not only volatile: it reacts with water to give sulfuric acid, giving their lachrymal properties to onions. The good news is that, as this sulfinyl is combustible, lighting a candle next to your cutting board should eliminate most of the annoying molecule.
Sulfur compounds can mean a more enjoyable experience too. A characteristic element of the taste of the Sauvignon Blanc wines rests on certain thiols. Interestingly, those thiols are absent from the wine itself. They originate from S-(R/S)-3-(1-hexanol)-L-cysteine, a component of the grape, which is transformed by salivas’ microflora in volatile thiols. Sulfur can have its upside too after all.

Further readings:
Jones MG et al. 2004 Biosynthesis of the flavour precursors of onion and garlic, J. Exp. Bot., 55 ( 404), 1903
Srarkenman C. 2008 Olfactory Perception of Cysteine-S-Conjugates from Fruits and Vegetables J. Agric. Food Chem., 56, 9575-80

Kitchen Blues

If a biochemist can be spotted by its blue-stained fingers, the color blue might be often overlooked in the kitchen. For this first column, we will turn our attention to two blue ingredients in our kitchens: red wine and bananas.
Blue hides in red wine. Anthocyanins give its color to the royal drink: those polyphenols gives in fact their colors to many flowers, fruits, berries and vegetables. Among which we can name pansies, eggplants, cherry, apples, raspberries, blueberries and grape. Acting as a natural sunscreen, anthocyanins protect the plants from the lights radiations that chlorophyll itself does not absorb or in other occurrences from other oxidative damage. Funny thing about them: their absorbance spectrum vary in a pH-dependant manner; red for acidic solutions, blue for alkaline and purple around neutral (anyone ever wondered where the Litmus test came from?).
Here is the funny hands-on part : to make some blue (and unpalatable) wine, just add some alkali to your red wine! 1M NaOH should do the trick (watch out : too much of it just gives a nasty brown). And duh… do I really need to tell you not to drink the wine afterward?
We have seen that red can be blue. Now, let’s see why, when bananas are involved, yellow also can be blue… Yes, they are blue. No? You were not looking at them under the right light: try UV instead (have you never brought a banana in a bar?). Your banana will turn a bright, electric blue. During ripening, as chlorophyll is degraded, bananas lose their green color, with only some carotenoids left to give the usual yellow. Chlorophyll being a porphyrinoid, its breakdown products can present surprising light-absorption characteristics. It appears that the secret of that fluorescent surprise resides in one of those metabolites, only recently discovered and termed FCC-56 (Fluorescent Chlorophyll Catabolite). Now, biochemists just have to figure the exact role of those metabolites for the plant... Piece of cake

For further reading about anthocyanins and wine color:

Jensen J. S. et al. 2008 Prediction of Wine Color Attributes from the Phenolic Profiles of Red Grapes (Vitis vinifera) J. Agric. Food Chem., 56 (3), 1105–15
The discovery of the fluorescence in bananas (how come no one saw that before?): Moser S. et al. 2008 Blue Luminescence of Ripening Bananas Angewandte Chemie. 47(46), 8954-7

Taste of Science

Taste Of Science is a column I have been writing for the BMI Bulletin since last autumn.
(http://intermed.med.uottawa.ca/Associations/BMIGSA/bulletin.htm)

Writing about the science of food is a great pleasure of mine, and I welcome the opportunity to share that interest with my colleagues among the biochemistry, microbiology and immunology department of the university of Ottawa.