A Little Bubbly

It is well known among champagne connoisseurs that you can tell the quality of the product by the nature of its bubbles (http://www.ehow.com/how_2192062_tell-good-champagne-its-bubbles.html). The flute should be adorned with a dainty pearl necklace of delicate effervescence. But what exactly determines the character of these bubbles? The rate at which they are formed and their longevity are both dependent upon the composition of the adsorption layer at the liquid/air interface. This adsorption layer is simply the aggregation of molecules on the surface of the champagne. It is known that the adsorption layer consists primarily of macromolecules (macromolecules include proteins, carbohydrates, fats, and nucleic acids), but its specific composition remains unclear. However, Aguié-Béghin et. al. (appropriately from the Université de Reims Champagne Ardennes) report their preliminary findings on the chemical composition of the adsorption layer in champagne (which they produced in the lab—I wonder if there would be a market for that…). The article abstract can be found here.

The researchers relied primarily on three methods of investigation for this study. First, they performed ellipsiometry (http://en.wikipedia.org/wiki/Ellipsometry) allowing them to determine the amount of time required for an adsorption layer to form. They used Brewster Angle Microscopy (BAM - http://users.otenet.gr/~garof/Bam/) to visualize the interface of champagne adsorbed onto a polystyrene surface, as a model for the liquid/air interface. Finally, the group performed X-ray photoelectron spectroscopic (XPS) studies to determine the chemical composition of the champagne surface (again as modeled by application of a champagne layer to polystyrene). XPS utilizes high-energy X-rays to disrupt electrons from the surface, and the energy needed to cause these electrons to escape is characteristic of the particular elements and the way in which they are bonded (http://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy).

Ellipsiometry was used to compare the rate of formation of the adsorption layer of champagnes at significantly different concentrations. The most highly concentrated (i.e. the sample containing the most macromolecules per unit volume of liquid) formed an adsorption layer the fastest, suggesting that these macromolecules do in fact play an important role in the formation of this surface layer.

Samples of champagne on the polystyrene layer were prepared in three different ways (soaking in champagne, soaking followed by rinsing with water, applying a layer of champagne and allowing it to evaporate), and visualized using BAM. The images demonstrate that the adsorption layer is heterogeneous, with regions showing aggregation of macromolecules in organized structural forms known as domains. This is consistent with previous findings at the liquid/air interface of champagne, and gives credence to the use of the polystyrene layer as a model for the liquid/air interface.

The XPS data reveal the ratios of different elements in the surface layer, and also provide some insight into the functional groups present in the macromolecules. Upon comparison with the composition of typical proteins, polysaccharides (i.e. sugars), and lipids (i.e. fats), the group was able to support the suggestion that the adsorption layer of champagne is composed primarily of proteins and polysaccharides, in the ratio of 35% protein to 65% polysaccharide. The data suggest that lipids are not present in the surface layer in any great quantity, which is atypical for many food products and biochemical mixtures, where lipids usually have a tendency to aggregate on the surface.

The specific identities of these proteins and polysaccharides, as well as the role that each plays at the champagne/air interface and thus in the formation and stability of bubbles, remains to be elucidated. However, these results do give some insight into the make up of the adsorption layer, and point to particular targets for further analysis. I’ll drink to that – Salut!

Aguié-Béghin, V.; Adriaensen, Y.; Péron, N.; Valade, M.; Rouxhet, P.; Douillard, R. Sturcture and Chemical Composition of Layers Adsorbed at Interfaces with Champagne. J. Agric. Food Chem. [Online early access]. DOI:10.1021/jf9016948. Published Online: October 8, 2009. http://pubs.acs.org/journal/jafcau (accessed October 23, 2009).

No More Green Eggs and Ham: Flavor Development in Dry-Cured Spanish Jamón

In Spain, ham is a way of life. Not only does jamón feature prominently on most traditional Spanish tables, but its unique flavor profile also occupies the time and resources of many Spanish scientists. And all for good reason – Spanish dry-cured hams are some of the most delectable in the world, and who wouldn’t like to know the reason for that? In the current issue of the American Chemical Society’s Journal of Agricultural and Food Chemistry (JAFC), a group of scientists from Britain and Spain report their latest findings on the biochemical changes that occur during the curing process and contribute to the characteristic flavor and texture of jamón (the abstract can be found here). Others have previously determined that the lengthy curing process (which can last anywhere from nine months to more than two years and involves at least five steps – refrigeration, salting, resting, drying, and ripening) facilitates the degradation of muscle proteins into their constituent parts, known as amino acids. These amino acids can be thought of as the alphabet from which all proteins “words” are formed, contributing to the enormous diversity of proteins in existence. Free amino acids are known to impart a variety of flavors in both animal- and plant-based foods, and one, glutamic acid, is responsible for the distinctive “fifth taste” of umami.

In the JAFC article, Mora et al. investigate the degradation of creatine kinase (CK), a particular protein found in muscle cells. Physiologically, CK is involved in cell metabolism (breakdown of chemical substances into the cell’s primary unit of energy – adenosine triphosphate, or ATP), but it also plays a role in converting muscle to meat, and its degradation seems to be related to meat quality. Using samples from traditionally cured hams, the scientists were able to distinguish 58 different peptide sequences (a peptide is a chain of amino acids too short and simple to be considered a protein), which are the fragments of CK resulting from degradation by enzymes (proteins with the ability to catalyze biochemical reactions - in this case, cleavage between two particular amino acids). The scientists used a technique known as MALDI-TOF mass spectrometry to distinguish the peptides, separating them by mass, thus allowing the researchers to determine the sequence of each peptide. By comparing the peptide sequences both with each other and with the complete protein sequence, Mora et al. were able to determine which types of enzymes are likely to be responsible for the protein degradation that occurs during dry-curing, as the enzymes are known to cleave at specific locations in peptide sequences. They found that two major classes of enzymes are involved, exopeptidases (exo- meaning outer, -ase being the suffix denoting an enzyme – thus an enzyme which cleaves an particular amino acid from the end of a peptide chain) and endopeptidases (endo- meaning inner – so an enzyme responsible for cleaving a peptide chain anywhere other than the ends). Many such enzymes have been found in hams after 12-15 months of curing, and seem to be the major facilitators of free amino acid production in dry-cured ham.

The JAFC paper provides further evidence of protein degradation in dry-cured Spanish hams, with the characterization of nearly sixty peptide fragments of the CK protein. Moreover, the existence of these fragments suggests the action of exo- and endopeptidases in the liberation of free amino acids from muscle proteins during curing. Understanding of these processes provides insight into the generation of the unparalleled flavor and texture of Spanish jamón. A more robust understanding of this flavor profile could allow us to modify the curing procedure to further enhance desirable flavors, or may even allow us to appropriate combinations of flavor molecules unique to jamón and creatively apply them to other food products.

Mora, L.; Sentandreu, M.A.; Fraser, P.D.; Toldra, F.; Bramley, P.M. Oligopeptides Arising from the Degradation of Creatine Kinase in Spanish Dry-Cured Ham. J. Agric. Food Chem. [Online] 2009, 57, 19, 8982-8988. http://pubs.acs.org/doi/abs/10.1021/jf901573t (accessed October 15, 2009).

The Empirical Epicurean: The Premise

There is a communication barrier between scientists and non-scientists. The danger of carcinogenic compounds, environmental policy suggestions, and the risk of nuclear power all become misconstrued in the public eye as a result of the difficulty of translating the results of scientific study into public knowledge. This challenge is four-fold:

• The inaccessibility of scientific jargon.
• Relatedly, the specificity of scientific knowledge. Not only must scientists engage in rigorous training for upwards of eight years, but even trained scientists often cannot decipher journal articles from another field of research, so how can someone with little to no formal training in the sciences hope to decipher the scientific literature?
• Speaking of the literature, the format of reporting scientific work is to publish articles in scientific journals, which, besides being literally inaccessible to most people (annual subscriptions to most journals range from about $80 to $300 and are typically provided by the home institution of scientists and students), are written in a format that is unique to the science world and rather tedious and impenetrable for those unaccustomed to the style.
• Finally, there is a misconception about the finality of scientific discovery. Science is a fluid entity, meant to continually change as experimentation and theory evolves to encompass new discoveries. This means that what we consider true today will not necessarily be accepted even ten years from now. A quick look at the history of science reveals the malleability of scientific understanding, as very little in science withstands the test of time. However, science carries great authority in today’s society, often giving off an air of infallibility. Thus scientific “discoveries” are often regarded as absolute fact, when in reality they are no less subject to scrutiny than the idea of a flat earth.

Thus we desperately need to break down this communication barrier and allow unimpeded discourse between scientists and nonscientists of all varieties. Though this may seem to be a lofty goal, we can start with baby steps, and such is the purpose of this blog.

I am a student of chemistry, biology, and so-called “science studies” – an interdisciplinary brand of social science which seeks to situate scientific activity in its cultural, political, historical, and economic context – but food is my passion. This blog is an exercise in uniting these interests, and was inspired by a physical chemistry professor with an eye toward uncovering the science of everyday phenomena. I will survey the academic literature as it relates to cuisine, and present a short summary of an article in terms that nonscientists (as well as scientists in fields other than the one discussed) can understand. I will pull primarily from the chemical and biological literature, but also hope to explore physics and even, occasionally, the realm of social science. Food has always been known as a phenomenal tool for building bonds between people, and thus I believe that it is the ideal topic through which to bridge the divide between scientists and nonscientists. And after all, as famed French gastronome Jean Anthelme Brillat-Savarin astutely noted,

“The discovery of a new dish confers more happiness on humanity, than the discovery of a new star.”