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| Clarifying the physical properties of chocolate to establish how to make tasty chocolate |
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Professor Satoru Ueno specializes in food—particularly oils and fats. He is renowned for his research on chocolate, one of the solid fat foods.
Prof. Ueno says “High quality foods are delicious. In other words, good taste has something to do with good quality. That’s why I am studying the physical properties of chocolate in such detail.”
He is an expert on biomolecular physical chemistry, an academic discipline that aims to clarify the physics phenomena of food component materials.
The prime ingredient of chocolate is cacao beans. Chocolate is made by adding sugar and milk to a mixture of cocoa butter, a fat extracted from cacao beans, and cocoa powder, which corresponds to the residue left after the cocoa mass and butter have been removed. |
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He states that “Human senses are delicate enough to distinguish slight differences in chocolate’s unique physical properties, such as smooth melting in the mouth, pleasant feel on the tongue, firmness to the tooth, and hardness felt when eating chocolate. Tasty chocolate excels in these sensory attributes.” These attributes are collectively known as its “textures.”
“Chocolate with an unpleasant texture does not taste good. For example, amateurish hand-made chocolate for Valentine’s Day does not taste good, does it?” says Prof. Ueno. Looking back on the long history of chocolate, he considers that chocolate made at around the time of the Industrial Revolution must have been unpalatable.
He explains that “Various ideas were incorporated to devise better chocolate-making methods. Such efforts eventually led to the development of a technique to make tasty chocolate products, as exemplified by the commercial chocolate bars that we now enjoy. Even without theoretical understanding, the techniques to make tasty chocolate became established. Then chocolate began to be mass-produced in the United States.” |
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| Temperature and crystal polymorphism are the keys to making tasty chocolate |
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The processes that are necessary to make tasty chocolate are roughly summarized as follows: First, decrease the temperature of melted chocolate to about 25 ℃ and let it stand for a while. Then raise the temperature to 30 ℃ or so. After waiting a while, lower the temperature again to approximately 20 ℃ to solidify the chocolate.
This temperature control technique is called “tempering,” and it is used even now by almost all confectionary companies and chocolatiers around the world, in order to make tasty chocolate.
Prof. Ueno explains that “This technique was invented more than 100 years ago. However, it was not until the 1980s that its theory was clarified.”
According to the professor, the theory is related to the physical properties of cocoa butter. “When cocoa butter is cooled and solidified, it becomes crystallized. In crystalline state, lipid molecules are arranged in an orderly fashion. There are several patterns of arrangement, and substances with the same chemical composition can have different crystal structures. This phenomenon is called “polymorphism,” in technical terms. |
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For example, there are a number of substances that are composed of exactly the same thing—carbon atoms—but exhibit different crystal structures. Typical among them are fullerene, diamond and graphite (often used as pencil “lead”). In the case of chocolate, cocoa butter can take on six different polymorphic forms, generally numbered with Roman numerals from I to VI.
Prof. Ueno points out that “Tasty chocolate selected by many people has always a certain crystal structure — that is, Form V. Chocolate manufacturers around the world are desperately working to develop a technique to ensure that the cocoa butter can be crystallized into Form V.”
In addition, since everyone considers chocolate tempering to be a troublesome task, technological development is under way to explore how to improve tempering efficiency. “For now, we have found that stirring and the use of ultrasound are effective ways. In terms of physics, stirring means to apply shearing stress, which I think is most promising. So I am studying the theory of stirring, through various approaches.” |
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| Using synchrotron radiation in research, to instantly capture the motion of a molecule, even when it is in a very small quantity |
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His research is characterized by the use of an electromagnetic radiation called “synchrotron radiation.”
Prof. Ueno says that “Synchrotron radiation is one of today’s cutting-edge scientific research techniques. By using synchrotron radiation, we can see the “motion” of molecules, i.e., how molecules will change. Metaphorically speaking, when synchrotron radiation is not used, I feel as if I am viewing a still manga image, whereas when it is used, I feel as if I am watching the action in an animation. With this technology, we can also analyze a research sample even when it is available in only a very small quantity. Moreover, synchrotron radiation has enabled us to measure a sample in one second or so, a process which previously took ten minutes. I personally find this technology to be truly interesting.”
He has also received an increasing number of requests to deliver lectures regarding his research, in which he makes effective use of cutting-edge science to study chocolate, a substance rather familiar to us.
Prof. Ueno continues that “Nowadays it is said that more people are moving away from the sciences. I therefore hope to let them know about familiar examples from everyday life, in which science has been applied.” In fact, when he was a graduate student, his research subjects were not foods but phospholipids. However, later he decided to pursue biophysics since he wanted to study something closer to living things.
Smiling, he expresses his future plans, saying “I will intensify my efforts to study chocolate, while also undertaking research into raw chocolate and ice cream.”
Studies on the crystal structures of chocolate are classified among what is called the “physics of complex systems,” which involves great difficulties. Nevertheless, the way he talks about his research is quite cheerful.
“Cocoa butter contains several kinds of fats, and there are a few hundred types of fat molecules. For this reason, it is very difficult to clarify the crystal structures of chocolate. On the other hand though, I believe that this work is all the more worthwhile. I hope that my research will provide a breakthrough in this discipline, someday in the future.” |
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| Satoru Ueno |
Professor
Laboratory of Biomolecular Physical Chemistry
Department of Biofunctional Science and Technology
May 1, 1992 – September 30, 1997 Lecturer, School of Applied Biological Science, Hiroshima University
October 1, 1997 – March 31, 2002 Associate Professor, School of Applied Biological Science, Hiroshima University
July 1, 2000 – December 15, 2000 Visiting Researcher, Department of Chemical & Process Engineering, The University of Sheffield, UK
April 1, 2002 – March 31, 2010 Associate Professor, School of Applied Biological Sciences, Hiroshima University
April 1, 2010 – present Professor, School of Applied Biological Science, Hiroshima University
Posted on Apr 18, 2016
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