NMR spectroscopy: a weapon against fraud in the food industry?
For the food industry and regulators, it is vital to be able to verify the authenticity of foods. This has been highlighted on an international scale by recent food scandals, such as the 2008 melamine poisoning in China and the 2013 meat adulteration scandal in Europe.
However, traditional methods of analysis suffer from a number of limitations. An important factor is that they are specific – meaning you need to know which compound or compounds you are looking for. Another is that while methods, such as chromatography, may provide a detailed profile of a foodstuff, they often require substantial sample preparation and are labor-intensive, expensive and time-consuming.
Therefore, in order to tackle the issue of food adulteration – the deliberate or accidental contamination of foodstuffs with banned substances – the food industry needs rapid methods of non-specific analysis.
Nuclear magnetic resonance (NMR) spectroscopy is a method that is gaining ground in food analysis, and has been successful in characterizing products such as beer, juice and infant formulas. It has the advantages of being able to reveal multiple components of a foodstuff on a single spectrum and, with the help of automation, can deliver rapid throughput analysis.
A 2013 study by Monakhova et al. explored whether NMR spectroscopy could be used to identify imitation cheese and ice cream. These are products in which the milk fat and/or milk protein components have been replaced with non-milk components, such as soy, starch or vegetable replacers. In the case of ice cream, vegetable oils and fats are often used as cheap substitutes for milk fat.
The researchers analyzed 109 cheese samples and 112 ice cream samples using a Bruker AVANCE spectrometer coupled to a Bruker Automatic Sample Changer. They first extracted the fat fraction from the products using hydrolysis, in a procedure known as the Weibull-Stoldt methodology.
Via NMR spectroscopy and principal component analysis (PCA), they found that imitation and genuine products formed distinct clusters according to their fatty acid profile. The clearest discrimination was in cheese products, while in ice cream, discrimination was less clear due to the variability of other minor compounds.
The researchers were then able to use loadings plots to identify the key spectral regions that could differentiate between milk fat and vegetable fat.
Additionally, they found that specific cheeses had distinct fatty acid profiles, allowing them to use the technique to identify Edam cheese from Gouda, Feta and Emmental.
And, NMR spectroscopy did not just provide qualitative information. By correlating NMR data with that from gas chromatography, Monakhova et al. were able to show that the technique could be used to accurately quantify the fatty acid components of samples.
The researchers say that their findings show the potential of NMR to provide rapid analysis of dairy products. They note that, because it provides a wide range of spectral information, it is ideal for nontargeted analysis and, combined with automation, allowed a high number of samples to be analyzed in a short period of time. Thus, it could prove a valuable tool for classifying food samples and detecting fraud in the dairy industry.
Monakhova Y, et al. Identification of imitation cheese and imitation ice cream based on vegetable fat using NMR spectroscopy and chemometrics. International Journal of Food Science 2013; 367841.
Sharma K, Paradakar M. The melamine adulteration scandal. Food Security 2010; 2: 97-107.