Winterová R., Mikulíková R., Mazáč J., Havelec P. (2008): Assessment of the authenticity of fruit spirits by gas chromatography and stable isotope ratio analyses. Czech J. Food Sci., 26: 368-375.The gas chromatographic (GC) determination of volatile constituents and the determination of 13 C/ 12 C isotope ratios by isotope ratio mass spectrometry -IRMS analysis as well as SNIF-NMR analysis of (D/H)I and (D/H)II ratios in ethanol are prospective analytical methods which can be used for checking the authenticity of fruit spirits and for detecting their adulteration. Different concentrations of volatile compounds such as acetaldehyde, ethyl acetate, diethyl acetal, methanol, 1-butanol, 2-butanol, 1-propanol, 2-methyl-1-propanol, 2-and 3-methyl-1-butanol, volatile fatty acids and isotopic data were demonstrated using discriminant analysis. The results show that the determination of isotope ratios can be used especially for distinguishing between fruit spirits and others spirits, i.e. those made from beet sugar, maize, cane sugar, grain, potato, or synthetic alcohol. Gas chromatography also makes it possible to discriminate between respective spirits derived from one kind of fruit such as sweet cherry brandy, sour cherry brandy, pear brandy, apple brandy, apricot brandy, or plum brandy.

A collaborative study of the carbon-13 isotope ratio mass spectrometry (13C-IRMS) method based on fermentation ethanol for detecting some sugar additions in fruit juices and maple syrup is reported. This method is complementary to the site-specific natural isotope fractionation by nuclear magnetic resonance (SNIF-NMR) method for detecting added beet sugar in the same products (AOAC Official Methods 995.17 and 2000.19), and uses the same initial steps to recover pure ethanol. The fruit juices or maple syrups are completely fermented with yeast, and the alcohol is distilled with a quantitative yield (>96%). The carbon-13 deviation (δ13C) of ethanol is then determined by IRMS. This parameter becomes less negative when exogenous sugar derived from plants exhibiting a C4 metabolism (e.g., corn or cane) is added to a juice obtained from plants exhibiting a C3 metabolism (most common fruits except pineapple) or to maple syrup. Conversely, the δ13C of ethanol becomes more negative when exogenous sugar derived from C3 plants (e.g., beet, wheat, rice) is added to pineapple products. Twelve laboratories analyzed 2 materials (orange juice and pure cane sugar) in blind duplicate and 4 sugar-adulterated materials (orange juice, maple syrup, pineapple juice, and apple juice) as Youden pairs. The precision of that method for measuring δ13C was similar to that of other methods applied to wine ethanol or extracted sugars in juices. The within-laboratory (sr) values ranged from 0.06 to 0.16‰ (r = 0.17 to 0.46‰), and the among-laboratories (sR) values ranged from 0.17 to 0.26‰ (R = 0.49 to 0.73‰). The Study Directors recommend that the method be adopted as First Action by AOAC INTERNATIONAL.

The results of collaborative study are reported for a method that determines the site-specific isotope ratios of deuterium/hydrogen (D/H)i in vanillin by deuterium-nuclear magnetic resonance (2H-NMR) spectrometry. This method allows characterization of all the main commercial sources of commercial vanillin and detection of undeclared mixtures. It is based on the fact that the amounts of deuterium at various positions in the vanillin molecule are significantly different from one source to another. Vanillin is dissolved in acetonitrile and analyzed with a high-field NMR spectrometer fitted with a deuterium probe and a fluorine lock. The proportions of isotopomers monodeuterated at each hydrogen position of the molecule are recorded, and the corresponding (D/H) ratios are determined by using a calibrated reference. Nine laboratories analyzed 5 materials supplied as blind duplicates (1 natural vanillin from vanilla beans, 2 synthetic vanillins from guaiacol, 1 semisynthetic vanillin from lignin, and a mixture of natural and synthetic vanillins). The precision of the method for measuring site-specific ratios was as follows: for (D/H)1 the within-laboratory standard deviation (sr) values ranged from 2.2 to 5.8 ppm, and the among-laboratories standard deviation (sR) values ranged from 3.6 to 5.1 ppm; for (D/H)3 the sr values ranged from 1.7 to 3.2 ppm, and the sR values ranged from 2.4 to 3.7 ppm; for (D/H)4 the sr values ranged from 2.3 to 6.2 ppm, and the sR values ranged from 2.4 to 6.4 ppm; for (D/H)5 the sr values ranged from 0.8 to 2.7 ppm, and the sR values ranged from 0.9 to 2.3 ppm. It was shown that these values allow a satisfactory discrimination between vanillin sources. Therefore, the Study Director recommends the method for adoption as a First Action Official Method by AOAC INTERNATIONAL.

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V posledních letech se objevilo podezření na falšování octů přídavkem syntetické kyseliny octové. Detekce falšování je založena na sledování markerů indikujících nedodržení technologického postupu, snížení obsahu přirozených složek suroviny nebo složek vznikajících při octovém kvašení. Falšované octy mohou obsahovat také složky vnesené syntetickým produktem, prekurzory z výroby. Možnosti použití chemometrických markerů jsou omezené; v případě kvasných octů je možné využít stanovení složek výchozích surovin, u lihových octů je však produkt obvykle velmi čistý. Nejspolehlivějším nástrojem pro autentizaci octů se jeví izotopová analýza SNIF-NMR a IRMS.