Determination of δ¹³C of vanillin in complex food matrices by HS‐SPME‐GC‐C‐IRMS

Abstract

Vanilla is one of the most popular spices in the world and is therefore often added to food products to enhance the taste with its desirable flavour. Vanilla flavour is highly susceptible to economically motivated food fraud since the main component ‘vanillin’ can easily be produced by much cheaper synthetic processes. The determination of the vanillin source is not always an easy task, especially when very low concentrations are incorporated in complex food matrices. Here, we present an easy sample preparation procedure that includes a solid‐phase extraction clean‐up to determine the isotopic carbon ratio of vanillin in food products by headspace solid‐phase microextraction and gas chromatography coupled to isotope ratio mass spectrometry. Isotopic fractionation during the sample preparation procedure was carefully evaluated. The method was applied to 23 commercial food samples including vanilla sugar, dairy and soy products. The study illustrates the potential and limitations of the authentication of vanilla flavour by the isotopic carbon ratio of vanillin. Further, the complexity of the authenticity assessment of vanilla flavours in composite food is demonstrated.

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

“…whereas values in the range from −36.2‰ to −24.9‰ are observed for samples of synthetic origins [23,33]. Considering all the possible routes for the synthesis of bio-vanillin, the δ 13 C range of values observed is from −37.8‰ to −12.5‰, depending on the specific source (rice, clove, wheat, turmeric, corn, and sugar cane) and the molecule used as a precursor (Figure 2) [34][35][36][37].…”

“…In recent years, carbon stable isotope analysis has been employed as a useful tool to differentiate between natural and artificial forms of vanilla extracts [20][21][22][23][24][25]. Vanilla is the second most expensive spice and is used as a flavoring component in the food industry.…”

“…In this context, the measure of the carbon stable isotope ratio (δ 13 C) becomes very useful. The δ 13 C value of a vanillin sample of natural origin is around −20‰, being a CAM (Crassulacean acid metabolism) plant extract, whereas values in the range from −36.2‰ to −24.9‰ are observed for samples of synthetic origins [23,33]. Considering all the possible routes for the synthesis of bio-vanillin, the δ 13 C range of values observed is from −37.8‰ to −12.5‰, depending on the specific source (rice, clove, wheat, turmeric, corn, and sugar cane) and the molecule used as a precursor (Figure 2) [34][35][36][37].…”

“…Considering all the possible routes for the synthesis of bio-vanillin, the δ 13 C range of values observed is from −37.8‰ to −12.5‰, depending on the specific source (rice, clove, wheat, turmeric, corn, and sugar cane) and the molecule used as a precursor (Figure 2) [34][35][36][37]. Moreover, the δ 13 C value of vanillin from vanilla beans ranges from −22.2‰ to −14.6‰ according to the type of plant (Vanilla pompona, Vanilla planifolia, and Vanilla tahitensis) and the geographic origin [23,34]. Although IRMS is the preferred method for the authentication of vanillin source, the δ 13 C measured can be easily manipulated by adding synthetic 13 C-depleted vanillin or by mixing vanillin samples from different cheap sources.…”

“…The IRMS method does not distinguish the carbon stable isotope ratio of the single compound from a complex matrix. In some cases, a purification pretreatment of samples with chromatographic methodologies is necessary [23,37]. Several scientific efforts are devoted to resolving this issue via the implementation of SNIF-NMR (site-specific natural isotopic fractionation by nuclear magnetic resonance) methodology [38,39].…”