NMR-spectroscopic applications to control coffee authenticity

Authenticity of coffee is an increasingly important issue in food control. A food is considered authentic if its characteristics match the declaration. For coffee, these can be characteristics such as the species, the geographical origin or the cultivation method used. Verification of coffee authenticity can be performed with proton nuclear magnetic resonance (¹H-NMR) spectroscopy with targeted or non-targeted approaches. In targeted methods, the identification and quantification of specific compounds is carried out. In contrast, the non-targeted method focuses on detecting as many constituents as possible without identifying or quantifying them. This allows a specific pattern to be detected, which is also known as a chemical fingerprint. These patterns can then be used to distinguish two classes of samples.
An example of the application of ¹H-NMR spectroscopy in a targeted approach is the differentiation of the species Coffea arabica and Coffea canephora. The distinction is achieved by quantifying the compound 16-O-methylcafestol, which is only present in Coffea canephora. Moreover, the coffee constituents 5-hydroxymethylfurfural, trigonelline, N-methylpyridinium, formic acid, chlorogenic acid, caffeine, acetic acid, and lactic acid can be quantified by ¹H-NMR spectroscopy in order to verify the coffee quality.
The analysis of authentic coffee samples by ¹H-NMR spectroscopy in combination with multivariate data analysis allows the detection of differences and specific patterns. Based on this, classification models ban be built. The created classification models can then be used to verify the authenticity of new, unknown coffee samples. This methodology was used to investigate the authenticity of coffee in terms of the geographical origin, the type of cultivation as well as the roasting process and the degree of roast. The geographical origin was considered first at continent by continent and then at the level of countries, with Ethiopia, Brazil, and Colombia being studied in more detail. The cultivation method was considered in relation to organic and conventionally produced coffee. The results of the non-targeted approach showed that it is possible to verify the authenticity of coffee with respect to both the continents and the countries Ethiopia and Brazil. A distinction between organically and conventionally produced coffees was not achieved. In contrast, it was possible to distinguish coffees according to the roasting process and the degree of roast.