Detection of Sophisticated Adulterations of Natural Vanilla Flavors and Extracts:  Application of the SNIF-NMR Method to Vanillin and <i>p-</i>Hydroxybenzaldehyde

This paper describes recent progress in the isotopic analysis of the two main aromatic constituents of vanilla flavor (vanillin and p-hydroxybenzaldehyde (pHB)). Some improvements concerning the SNIF-NMR analysis of vanillin are presented. They include (i) improvement of the analytical precision by using new software for automatic phasing, baseline correction and curve fitting of the signals of the 2H-NMR spectra; (ii) significant enrichment of the database containing measurements performed on vanillin extracted from vanilla beans harvested in different countries and on synthetic vanillin; (iii) standardization of the purification process to obtain pure vanillin, in order to avoid isotopic fractionation; and (iv) improvement of the statistical tools for both proving and quantifying adulterations. All these improvements were also successfully applied to site specific deuterium NMR analysis of pHB. It is now also possible with the SNIF-NMR method to discriminate between the natural and chemical origins of pHB. New results concerning the δ13C deviation of pHB are also presented. Thus the lowest value of δ13C of pHB extracted from vanilla bean can be set at −19.5‰. We recommend the methodology presented in this paper as a standard procedure for purifying vanillin and pHB, without significant isotopic fractionation, from most matrices (for example from ice cream, yogurts, etc.), in order to perform isotopic analyses (13C IRMS and 2H-NMR). Keywords: SNIF-NMR; vanillin; pHB; δ13C; adulteration; vanilla flavor; vanilla extract; ice cream; purification