Determination of the 13C/12C Ratio of Ethanol Derived from Fruit Juices and Maple Syrup by Isotope Ratio Mass Spectrometry: Collaborative Study

Abstract

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.

Orange: Research analysis for wine study

“…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 and uses the same initial steps to recover pure ethanol. The precision of this method for measuring delta13C was similar to that of other methods applied to wine ethanol or extracted sugars in juices [30]. Analysis covers two important techniques, high resolution nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS); used to characterize food products and detect possible adulteration of wine, fruit juices, and olive oil, all important products of the Mediterranean Basin [31].…”

Application of 13C Quantitative NMR Spectroscopy to Isotopic Analyses for Vanillin Authentication Source

“…Furthermore, its determination gives the most important information concerning falsifications, adulterations, and fraud in food products [6]. For example, this method is the official method applied by the IOV (International Organization of Vines and Wine) [7] to quantify the sugar added into wine [8,9]. Isotope ratio mass spectrometry (IRMS) is the official methodology for the analysis of carbon stable isotope ratio due to its high accuracy (0.1‰) and sensitivity (up to 0.01‰) [10].…”

Authentication of Agave Products through Isotopic Intramolecular 13C Content of Ethanol: Optimization and Validation of 13C Quantitative NMR Methodology

“…2 H SNIF-NMR 13 was established more than 3 decades ago to assess wine and spirits authenticity through ethanol obtained by quantitative distillation in combination with 13 C irm-MS. 14,15 The scope of the method was extended later to ethanol obtained from fruit juice to detect exogenous sugar addition after controlled fermentation in the laboratory. 16,17 Unfortunately, this methodology failed to identify C 4originated sugar addition into product derived from CAM plants (crassulacean acid metabolism) such as pineapple or agave: expectedly, no significant differences were found between C 4 and CAM sugar ethanol using 2 H SNIF-NMR combined with carbon IRMS. 18 A few decades later, an equivalent method was developed to monitor 13 C/ 12 C ratio (irm- 13 C NMR, isotope ratio measured by 13 C nuclear magnetic resonance, or by analogy with 2 H/ 13 C SNIF-NMR).…”