Food Authenticity Determination by SNIF-NMR
Food authenticity is playing an increasingly important role in today's society, as the number of adulterated products is becoming higher and higher. Natural ingredients of food products, such as sugar, vanillin, terpene, can be checked for origin, purity, and authenticity. Special NMR systems, such as SNIF-NMR (Site-Specific Natural Isotope Fractionation Nuclear Magnetic Resonance) can be used to measure the hydrogen isotope ratios of nearly all natural products in order to determine the "history" of each product.
SNIF-NMR Spectroscopy was first used for food analytics by G.J. Martin in the late 1980s. At the beginning of the 90s, SNIF-NMR got its EU-wide approval as a method of analysis for food authenticity control.
SNIF-NMR Spectroscopy is based on the principle that plants do not incorporate natural Deuterium into their Glucose molecules according to a "statistic" pattern, but every proton of a plant molecule is substituted by Deuterium in a specific ratio, which is different for each kind of plant.
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| Fig. 1: Earth rotation causes different Deuterium proportions |
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SNIF-NMR was first used for a more precise determination of the origin, purity and authenticity of wine. As the natural abundance of Deuterium depends on the strength of the centrifugal force, which is different from longitude to longitude, the total Deuterium-hydrogen-ratio can be measured to determine the longitude of origin of the wine.
The second analysis includes the ratio determination of Deuterium protons on carbons C1 and C2 of ethanol, which in the best case can be used to determine the variety of vine. However, this is in general not necessary, as the most important issue is to find out whether sugar has been added to the wine before its fermentation. A significant shift in the C1/C2-deuterium ratio shows that the wine has been adulterated.
Based on wine authenticity determination, other plant products were analysed by SNIF-NMR spectroscopy. INFAI has conducted an analysis of different sorts of honey. Unlike wine, honey is produced from different kinds of plants. Therefore, different honeys have different colours. The original plant of a special kind of honey can also be determined by SNIF NMR, due to the specific ratio of deuterium protons on the glucose molecules of the plant.
However, as an analysis of glucose spectra by standard methods is not possible due to overlapping signal groups, an enormous amount of extra work is required. Alternatively, a method was developed, based on standard measuring methods of wine analysis. For this, yeast is added to honey. The honey will then be fermented. After fermentation, the ethanol obtained during this fermentation is analysed.
As early as during marketing authorisation application for SNIF-NMR, INFAI was involved in the process as a project partner for food control within the EU countries, thus being one of the most experienced certified partners in the field of SNIF-NMR.