A New Technique to Monitor Olive Ripening

After an extended final exam-induced hiatus, I am finally back! Fortunately, food research didn’t slow down while I was paralyzed by the onslaught of papers and studying, so I have articles about sake, caseins, and Pastis in the pipelines. But first let’s take a look at a strikingly simple method for tracking the maturation of olive fruits.

As olives grow and ripen throughout the summer and autumn months, the endocarp (pit) matures and hardens within six weeks of blooming, followed by the slow growth of the mesocarp (flesh) and exocarp (skin), primarily as a result of oil accumulation in the flesh. As it grows, the fruit morphs from a green color due to chlorophyll and carotenoid pigments to purple and then black as anthocyanins replace the other pigment molecules, demonstrating full ripeness by early winter. This visible transformation is mirrored by alterations in the molecular structure of the fruit, which have been measured by such analytical techniques as gas chromatography, which can separate and identify particular components, especially long-chained alcohols (triterpene alcohols) and sterols, and high performance liquid chromatography (HPLC), used to quantify the presence of ringed alcohol structures (phenolics), chlorophylls and carotenoids, and acidic compounds. However, both of these methods look only at particular groups of olive fruit components and are thus of limited practicality.

López-Sánchez, et al. report the effectiveness of vibrational spectroscopy for tracking the changing composition of olive fruits during maturation. Vibrational spectroscopy encompasses a set of techniques that analyze the unique interactions between different types of molecules and light. Through this type of analysis, chemists are able to determine the functional groups present in the sample. To study olive growth, López-Sánchez, et al. employ two of the most common examples of vibrational spectroscopy, infrared (IR) and Raman spectroscopy. These methods provide a broader analysis of fruit composition than the aforementioned chromatographic techniques. Moreover, vibrational techniques are quicker because the samples are much easier to prepare. Samples using intact olives can be taken of the skin, while only slicing and removal of the flesh are necessary to prepare samples of the flesh and pit. In the Spanish study, IR and Raman spectroscopy of ripe fruit confirmed the presence of water, lipids, and polysaccharides (especially cellulose and pectins) in the flesh, waxes and polysaccharides in the skin, and the woody compound lignin, along with water, in the pit. These data provide verification that these spectroscopic techniques are capable of discerning the compounds known to exist in each portion of the fruit.

An example of an IR spectrum - this is the spectrum of beta-carotene (Spectrum courtesy of SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/ (National Institute of Advanced Industrial Science and Technology, date of access)

Upon comparison of the spectra taken of olives at varying levels of maturity, the most prominent changes were observable in the mesocarp, and could be attributed to oil accumulation. As the olives mature, their spectra increasingly resemble those of pure olive oil, clearly indicating that the proportion of oil in the fruit is increasing. By measuring the change in the area of oil-specific peaks in the spectra over the ripening period (June to February), a three-phase trend was observed. Before hardening of the pit, there was no change in oil content. However, this period was followed by a rapid increase in oil between July and October, after which the oil level stabilized again. Due to an artifact of the IR spectroscopy technique, the IR data suggest that after a period of time the oil levels decrease, but this trend does not appear when Raman spectroscopy is used, or when oil levels are measured by the traditional method of oil extraction. The researchers posit that this apparent decrease is a result of the puncturing of cells as pressure is applied to ensure tight contact between the fruit and the ATR crystal (the effective light source for the IR spectrometer). Water is released as the cells burst, thus decreasing the apparent proportion of oil in the sample. This only occurs in ripe fruit because textural changes occur during the maturation process, rendering the ripe olive more delicate. Due to this artifact, the authors recommend using Raman spectroscopy, where samples can simply be placed in a holder for spectroscopic readings, rather than IR when investigating the structure of ripe olives.

By again comparing the areas of specific peaks over the ripening period, the researchers were able to track changes in phenolic and carotenioid compounds of olive flesh during growth. Phenolics were found to rapidly decrease before the pit hardened, and then gradually increase again until about September, at which point the compounds decreased again, finally stabilizing by early winter. This seemingly erratic trend can be explained by the dual origin of phenolic compounds in olives. Lignins and their precursors are phenolics, thus before the stone hardens, these compounds are abundant in the flesh, but as hardening, or lignification, occurs, they become sequestered in the pit, resulting in their observed decrease in the flesh. The subsequent trend is consistent with previously observed behavior of phenols in olive flesh, with a gradual increase followed by a sharp decrease as the fruit blackens.

Carotenoids follow a similar evolution as observed in the behavior of phenolics post-lignification. As the fruit grows, carotenoid content increases along with the increasing fruit mass. Once the olive is fully developed, carotenoid levels fall off, in correspondence to the color transformation from green to black, as carotenoids and chlorophylls are replaced by red-purple anthocyanin pigments. Notably, in analyzing the spectra taken from olive skins, the researchers noticed that as the skin thins upon maturation, the Raman spectra taken of whole, intact olives comes to more closely resemble that of the olive flesh, indicating that the lasers used in Raman spectroscopy are able to penetrate the fruit’s skin. This observation suggests that Raman spectroscopy of intact olives could be used to monitor changes in the flesh, such as oil accumulation. Raman spectroscopy thus appears to be a practically straightforward and non-invasive method for tracking the molecular changes associated with olive maturation and growth, and could be used to determine when to harvest the fruits to obtain the desired oil content.

López-Sánchez, M.; Ayora-Cañada; M.J.; Molina-Díaz, A. Olive Fruit Growth and Ripening as Seen by Vibrational Spectroscopy. J. Agric. Food Chem. Published online November 18, 2009.

Pierre Gagnaire brings Paris to Vegas all over again

When I wrote yesterday about the growing importance of molecular gastronomy in the United States, I didn’t realize I had become a prophet. This morning, I opened up nytimes.com’s dining page to find an article previewing Twist– Las Vegas’ next big restaurant due to open on December 4.How is this relevant? The restaurant is the new project of Pierre Gagnaire, the renowned three-starred French chef who is the friend and collaborator of Hervé This – cofounder of molecular gastronomy. The two men have coauthored a book (Cooking: The Quintessential Art) and created a website that presents a new recipe inspired by principles ascertained from the latest molecular gastronomy research each month. Gagnaire supplies the creative, artistic counterweight to This’ scientific discourse, infusing aesthetic vitality into the mechanical framework of molecular gastronomy. The relationship between these two men exemplifies the manner in which molecular gastronomy questions the supposed dichotomy between science and art – chipping away at the barricade that has been socially constructed between the “objective” and the “subjective.”

Twist will be Gagnaire’s first restaurant in the United States, and will supplement his global fleet – including outposts in Paris, Tokyo, Hong Kong, London, Dubai, and Seoul. He is still working to articulate his vision for the new restaurant, but told reporter Glenn Collins that “It will not be a brasserie, and not be a gastronomic restaurant. My way of cooking is very poetic and emotional. I would like this to be a place of tenderness — a word not often used in Las Vegas. After all, my only way of expressing myself is through my cooking... I am going to listen to try to understand the psychological profile, and the gourmet profile, of people coming to dinner.”Personally, I am willing to trust his judgment, and am thrilled to see another culinary institution bring attention to molecular gastronomy.

Molecular Gastronomy Newsflash!

My fascination with molecular gastronomy was a major impetus for the creation of this blog, and I am currently engaged in the research phase of a paper that will explore the role this field has had in shaping the public’s relationship to science. This continues to be a remarkably relevant matter, as evidenced by a fascinating article in the science section of yesterday’s New York Times. The article profiles Microsoft’s former chief technolofy officer (and master French chef) Nathan Myhrvold in his latest endeavor. Dr. Myhrvold has created a molecular gastronomy wonderland, a kitchen laboratory equipped with distillation apparatuses, autoclaves, hydraulic presses, and even the ex-food research manager at the Fat Duck – Heston Blumenthal’s world-renowned restaurant in Bray, England. Out of discoveries from this lab, which very nearly replicates my vision of heaven on earth, Myhrvold hopes to author the “authoritative reference for chefs wishing to employ so-called molecular gastronomy — adapting food industry technologies to restaurant cooking.” The book is headed toward 1,500 pages, and doesn’t sound like something most people would pack for a trip to the beach, but this will represent a departure from the only molecular gastronomy-esque instructional books thus far available in English, which are all written from a chef’s perspective (including The Big Fat Duck Cookbook, Under Pressure, Alinea, A Day at El Bulli). Myhrvold’s plans are incredibly exciting, as this type of work is still relatively rare in the United States, and reflect the growing importance of molecular gastronomy as a serious enterprise in this country.

Biomimetic Investigation of Coffee Flavor: A Wake Up Call for Reductionism

Food science tends to take a reductionist approach to evaluating complex foodstuffs, analyzing individual components and extrapolating the results to obtain a comprehensive, if somewhat artificial, understanding of the entire product. However, as is true for other scientific enterprises as well, this can result in an obscured impression of reality. For this reason, many scientists strive to develop experiments that allow them to probe as realistic a simulation as possible. In regards to biologically oriented fields, the term “biomimetics” has been coined to encapsulate such technologies. In their article investigating the aromatic profile of roasted coffee beans, Poisson et al employ biomimetic “in-bean” experiments to gain a more accurate understanding of the formation of odorant molecules during roasting (article abstract). Although previous studies have investigated flavor formation in coffee, the vast majority of these have been conducted using vastly simplified model systems that may not accurately reflect the normal processes occurring inside coffee beans. Studies comparing the flavor profiles of beans roasted whole to those ground before roasting have demonstrated the indispensability of the whole bean environment to normal flavor formation.

Poisson et al utilize a relatively new approach to circumvent the insufficiencies faced by experiments based on model systems. They extract the flavor-precursor molecules from unroasted, green coffee beans by soaking them in hot water. The beans can then be reconstituted either with the natural bean extract or with synthetic “biomimetic” solutions containing the most likely principle precursors to coffee bean flavor molecules (as suggested by experiments in model systems). The reconstitution step allows the scientists to intervene and alter the composition of the replenishing extract, so that they can trace the result of various precursors after the “spiked” beans have been roasted. By controlling the types of precursors present in the unroasted beans, the scientists can determine the effect of the presence or absence of particular precursors on the formation of various flavor molecules upon roasting.

The procedure also enables the to spike the beans with isotope-labeled precursors, which contain carbon-13 (heavier than the more abundant carbon-12 – see http://en.wikipedia.org/wiki/Isotope for more information on isotopes). Upon roasting, these carbon-13 labeled precursors are incorporated into odorant molecules, and can be identified using mass spectrometry (a technique that identifies molecules based on their masses – therefore if the mass is greater than expected for the compound containing only carbon-12, the difference between the expected and experimental value tells you how many carbon-13 atoms were incorporated). Therefore, if exhausted green coffee beans are spiked with only a particular labeled precursor, the scientists can trace which odorant molecules contain the carbon-13 isotopes (and can also identify the number of isotopes, and therefore the number of precursors incorporated). Such a determination of the fate of various precursors provides significant insight into the mechanism of formation of these odorant molecules during roasting.

Through use of this in-bean approach, Poisson et al were able to confirm many of the formation pathways proposed based on model systems. However this method also revealed a variety of alternative pathways that had not been suggested due to simplification in these models. Unlike previous experiments, the in-bean experiments allowed researchers to maintain the complexity of the coffee bean, and thus did not eliminate molecules that could be potentially important contributors to mechanisms of flavor formation. Though the researchers feel that improvements to this method are still necessary (optimization of the reconstituting mixture and reconstitution efficiency, for example), they stress the importance of biomimetic techniques in determining the nature of reactions that occur during food processing of any kind. This type of approach is analogous to in vivo studies in biomedical research, which are seen as an imperative step toward gaining a full understanding of biological processes. Food science must adopt such a standard, as in order to obtain the most accurate and informative results, studies of food processing and cooking must be performed under conditions as authentic as possible.

Poisson, L.;Schmalzried, F.; Davidek, T.; Blank, I.; Kerler, J. Study on the Role of Precursors in Coffee Flavor Formation Using In-Bean Experiments. J. Agric. Food Chem., [Online] 2009, 57 (21), 9923–9931. http://pubs.acs.org/doi/full/10.1021/jf901683v (accessed November 15, 2009).

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.”