news
research profiles Analyzing fermented beverages by microCE
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Tyramine
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sample derivatization and involve cumbersome, expensive instrumentation, the MOA protocol is relatively simple and the instrument compact. Mathies’s group incubated beverage samples with fluorescamine to label the
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The recent news about tainted pet food and toothpaste has increased pressure on regulators to improve the testing of consumer products for adulterants. Large-scale testing is hampered, however, by the time- and resource-intensive nature of the analytical methods. In this issue of Analytical Chemistry (pp 8162–8169), Richard Mathies and colleagues at the University of California Berkeley describe their efforts to develop a simple point-of-consumption testing platform by adapting technologies that they first developed to look for signs of life on Mars. Mathies’s group examined the biogenic amines tyramine and histamine found in various wines, beer, and sake. The amines, which are byproducts of microbial contamination or fermentation, are normally metabolized by monoamine oxidase. But in individuals who are deficient in the enzyme or who take monoamine oxidase inhibitors, the compounds can trigger symptoms such as nausea, hypertension headaches, and respiratory disorders. “Several years ago, in a chance dinner conversation with a colleague, I happened to mention that I had essentially stopped drinking wine because it caused me to suddenly awaken in the middle of the night with strong symptoms of hypertension,” Mathies relates. “My friend immediately responded that he had a similar problem and that this might be due to the effect of tyramine overstimulating the excitatory dopamine neurotransmitter pathways.” “Since tyramine is an organic amine, and we had developed a superb instrument for detecting organic amines, the idea of using the MOA to analyze for these components was born,” he adds. MOA is a microCE platform that Mathies developed for the European Space Agency’s 2013 ExoMars mission to detect primary amines in Martian soil (Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 1041–1046). Unlike LC/MS methods that can require complicated
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With microCE, Berkeley researchers can identify the biogenic amines histamine and tyramine in red wine.
amines, separated the compounds by microCE, and used fluorescence detection to generate electropherograms. The researchers found that red wines exhibited much more complex mixtures of amines and diamines than white wines and that beer gave rise to simple electropherograms of predominantly neutral amino acid peaks. They were surprised, however, by the high concentration of histamine in sake, which had levels 10× higher than those of many of the wines. “The moral is: if you are sensitive to histamine, stay away from sake when you visit Japan,” he adds. The researchers then examined samples from the different stages of wine fermentation, from “grape crush” to bottling. They found that histamine levels did not begin to rise until the first stage of fermentation, when yeast begins to convert the sugars. Tyramine, however, was not detectable until the second fermentation phase, when ma-
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lolactic bacteria convert malic acid to lactic acid. The histamine and tyramine levels continued to rise through fermentation and remained consistent up to 3 months after bottling. “It would be great if, in addition to measuring the concentrations of tyramine and histamine and making this information available to the consumer, we could figure out what fermentation processes produce lower amounts of especially tyramine,” Mathies says. “Right now, our study shows that the tyramine is produced in the malolactic fermentation step, but we do not know whether this is an absolutely necessary process in wine making or whether it can be modified to reduce the tyramine production.” Although he is pleased with the results to date, Mathies’s goal is to develop a truly compact and portable detection system for a wide array of applications. “The microchip and optical systems are currently quite small and compact. We simply need to fully integrate the electronics in order to dramatically reduce the instrument size and make it practical for real-time analysis.” He suggests that the introduction of new fluorescent derivatization reagents will allow his group to label different organic functional groups, enabling the development of analytical protocols for compounds such as carboxylic acids and sugars. He says his group is making progress on the detection and analysis of polycyclic aromatic hydrocarbons, which are of interest for space exploration and environmental applications. “Our study argues for more careful and complete analysis of the chemical contents of our food supply so that individuals who are sensitive to certain compounds, such as tyramine or histamine, can simply look on the label to find out if they should avoid a certain beverage,” Mathies says. “Consumers need and deserve this information, and analytical chemists with microchip systems can give it to them.” a —Randall C Willis
