Handbook of Vanilla Science and Technology

A new technique known as SNIF-NMR (site-specific natural isotope fractionation by nuclear magnetic resonance), was developed in 1988 by Gerard Martin at the University of Nantes, France. The natural replacement of hydrogen by its heavy isotope deuterium, in certain natural molecules, is measured by this technique.

The technique has been shown to be very useful in determining the authenticity of pure vanilla by determining the four site-specific natural isotope ratios (D/H) of its vanillin (Figure 9.6) by NMR (Maubert et al. 1988). Depending upon the source of vanillin, natural from vanilla beans, natural made by fermentation, or synthetic from lignin or guaiacol, these (D/H) ratios will vary due to the fact that physical, chemical, and biological processes enrich some materials with deuterium and deplete others. Rain water in the tropics, where vanilla grows, is relatively rich in deuterium (160 ppm). This deuterium concentration gradually decreases as we move away from the equator towards the North and South Poles. The rain (snow) water near the South Pole, for example, is only 90 ppm. The plants absorb rain water containing different concentrations of deuterium, depending on the region where they are growing. Altitude, distance from the sea, and level of rainfall of the growing area also affect the distribution of deuterium in local water and hence the site-specific ratios. All these factors and plant biochemical processes are responsible for particular level of deuterium enrichment at specific sites on the vanillin molecule. Vanillin molecules from different geographic origins and sources will have different site specific natural (D/H) ratios. Thus measurement of (D/H) ratios on all four sites on the vanillin molecule can precisely reveal its origin.

John and Jamin (2004) reported that the SNIF-NMR pattern of vanillin and p-HB for vanilla beans of Indian origin “showed significant differences from beans from other geographical sources.” They surmise this could be due to effect of latitude, altitude, distance from the sea, rainfall, etc. on the Indian vanilla growing areas. They, however, conclude that SNIF-NMR data can discriminate the vanillin and p-hydroxybenzaldehyde of the Indian beans from synthetic or semi-synthetic sources.

9.5 SUMMARY

The factors that define quality of vanilla beans and vanilla extracts have been reviewed in this chapter. Grading of vanilla beans based on appearance, aroma, taste, and vanillin content was explained. Aroma compounds, besides vanillin, in vanilla and their role in vanilla quality was described. Vanilla quality control parameters and their methods of analysis were presented. Values for the acceptable ratios of important marker compounds were presented. Methods for determining authenticity of vanilla products were described and the recommended authenticity values for ¹³C deviation (SIRA) and SNIF-NMR analysis were given. Information in this chapter should help vanilla growers, processors, suppliers, and vanilla products manufacturers to understand and maintain quality of vanilla. To vanilla consumers, big and small, the information can help in choosing the appropriate and best quality products in their applications.

ACKNOWLEDGEMENT

I want to thank my wife, Sunanda Ranadive, for reading and providing valuable comments and suggestions during the preparation of this manuscript.

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