Identifying Counterfeit Cognac
IR spectroscopy tested as a detector of faux products.
In the food and drink industry, counterfeit products are a big problem. In the spirits industry alone, annual losses due to counterfeiting are about €725 million worldwide, according to the International Federation of Spirit Producers. Further losses occur from substitution, where bar staff refill branded liquor bottles with cheap inferior products or simply water.
These normalized mean spectra of 41 cognacs were obtained by attenuated total reflection (ATR), and of dry extract and phenolic dry extract of the same products by transmission. Ethanol dominates the ATR spectrum of the raw product (peaks at 1085, 1045 and 878 cm–1) and masks the absorption bands of other compounds. Reprinted with permission of the Journal of Agricultural and Food Chemistry.
Detecting counterfeit products can be a time-consuming process that involves sending samples to a laboratory to be analyzed using traditional methods such as gas chromatography and high-performance liquid chromatography. Researchers in France, however, have been evaluating the use of mid-infrared spectroscopy to discriminate cognacs and other spirits. “Our aim is to develop an instrument that can be used on-site to detect counterfeit products,” said Daniel Picque from the Institut National de la Recherche Agronomique in Thiverval-Grignon.
Picque and his colleagues concentrated their work on differentiating cognac from other distilled drinks, such as Armagnacs, whiskeys, brandies, bourbons, rums and counterfeit products. Cognac is produced within a limited geographical area of France using defined white grape varieties and a specific manufacturing process that includes fermentation, two distillations and aging in oak barrels. The age of cognac is determined by the youngest product introduced into the blend, and aging the product is strictly regulated.
The researchers performed IR spectroscopy with a Thermo spectrophotometer and multivariated data analysis on more than 150 samples. They recorded the spectra of dry extract or phenolic dry extract of the products because, when analyzing a raw sample, the infrared spectrum shows mainly ethanol masking the absorption bands of other compounds. Drying the sample eliminates ethanol and water so that the other compounds, such as carbohydrates, caramel and extractible material from oak wood, are more visible in the spectrum. They successfully differentiated cognacs from other distilled beverages, assigning 96 percent of samples correctly.
The drying step allows better discrimination between cognac and other spirits, but it requires preparation. However, new attenuated total reflection (ATR) systems allow the sample to dry directly on the ATR crystal before analysis. “An ATR system, integrated into the spectrometer, could replace the polyethylene membrane used in our study,” Picque said. It would make this preparation step easy and fast, he added.
He and his colleagues are focusing on simplifying the analytical methods used in their work and ultimately on developing a user-friendly instrument to detect counterfeit products.
“IR spectroscopy offers several advantages over other techniques,” Picque said. “It is easy to use after calibration, is not time-consuming, can be used to analyze products without preparation and has the potential for at-line analysis.” He also believes that the combination of mid-infrared spectra with other analytical methods, such as UV-visible spectroscopy, and other data analysis techniques, such as neural networks, may enhance the ability to distinguish counterfeit from cognac and other genuine products.
Journal of Agricultural and Food Chemistry, July 26, 2006, pp. 5220-5226.
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