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NMR provides simple, rapid, and robust authentication of coffee

“Due to its versatility, reproducibility, and robustness, NMR is an excellent option  for use in improved coffee quality control procedures”

Coffee has been central to meetings, both social and business, for many years making it one of the world’s most popular beverages. Recently, there has been a shift towards premium coffee products with consumers being willing to pay more for their coffee. Although this has had a positive effect on the growth of the coffee bean market, it has also led to an increase in fraudulent trading practices.

The high potential for financial gain has made the coffee bean market a target for food fraud. Some producers are using deceit to increase profit margins by bulking out premium coffee products with cheaper substitutes. Rye, corn, barley, and even coffee husks have been found in marketed arabica coffee. Premium arabica coffee beans may also be mixed with lower quality bean varieties, such as robusta. With such rapid growth in the coffee trade, these unscrupulous practices are of mounting concern and highlight the critical need for reliable means of testing a coffee sample for adulteration. Such fraudulent activities must be stopped in order to protect the livelihoods of genuine suppliers.

Due to the high costs involved, strict regulations have been implemented to ensure the quality of coffee products. In Brazil, a stamp from the Brazilian Association of Coffee Industries (ABIC) indicates that the coffee has been analyzed and found to be unadulterated. However, the outdated analytical techniques employed by ABIC mean that some products with the ABIC stamp are not in fact genuine. More reliable analytical methodologies must be adopted in order to maintain confidence in the ABIC stamp.

With its ability to simultaneously, and non-destructively, identify and quantify all components of a complex mixture with minimal sample preparation, nuclear magnetic resonance spectroscopy (NMR) seems well suited to the detection of adulteration. Indeed, it has been used with great success in the quality testing of many foods and beverages. Furthermore, NMR has been used to identify robusta beans in arabica coffee.

The latest study evaluated the capacity of 1H NMR to detect bulking adulterants in coffee samples. Samples of pure coffee as well as those adulterated with barley, corn, coffee husks, soybean, rice, or wheat were analyzed by 1H NMR using a Bruker Avance III HD 600 spectrometer. Bruker TopSpin 3.2 software was used for data analysis and signal integrations. Comparisons of the spectra of pure and adulterated coffee samples were achieved using principal component analysis (PCA) and soft independent modeling of class analogies (SIMCA).

Without any previous separation, 1H NMR spectra were successfully obtained for several commercial ground coffee blends with different origins and extents of roasting. The limit of detection achieved was greater than that recorded in previous studies and was satisfactory in both medium and dark roast coffees (0.31–0.86%).

Adulterated coffee samples were identified with a 100% success rate using the SIMCA model. The key difference between pure and adulterated coffee samples was additional signals indicative of the presence of starch in the adulterated samples. By describing this signal pattern, the researchers have provided a reliable means to readily identify and quantify the presence of commonly used bulking adulterants, such as corn, barley, wheat, and rice, in coffee samples.

Milani MI, et al. Food Control 2020;112:107104. https://doi.org/10.1016/j.foodcont.2020.107104