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.