Although it is not an inviting statement, all food and beverages are nothing but a complex mixture of molecular compounds. The identification and quantification of these components are the basis of the quality control of commercial products, authentication, and discovery of food fraud.
Traditionally, laboratories employ chromatographic separation techniques, such as GC-MS and LC-MS, to characterize samples. However, these techniques require laborious system calibration and sample preparation, become expensive when run at industrial volume on a day-to-day basis, time-consuming and environmentally unsustainable when we think of the consumable required and the waste disposal.
On the contrary, fluorescence spectroscopy relies on the intrinsic ability of the sample to emit a characteristic signal when excited and, therefore, requires very little and easy sample preparation. Fluorescence EEM (excitation-emission matrix) is already a well-established technique, but one could argue that its ability to provide a molecular fingerprint of the mixtures is dependent on the concentration of the sample. In fact, the inner filter effect (IFE), the absorption of the excitation photons and the reabsorption of the emitted photons by the sample itself, will change the shape and intensity of the emission spectrum. To solve this, A-TEEM is introduced, a simultaneous Absorbance-Transmittance Excitation Emission matrix acquisition. A-TEEM is a novel technique that returns a quantitative molecular fingerprinting of the sample, based on data corrected from the IFE and, therefore, independent from its concentration. Highly sensitive and specific when compared to Raman spectroscopy and UV-VIS-NIR spectroscopy respectively, A-TEEM does not require complicated sample preparation and is greener than separation techniques. Repeatable and reproducible, it allows the creation of molecular libraries and the rapid detection of unknown components of the mixture.
The application of A-TEEM for analysis of food and beverages demonstrated that it provides unique sample fingerprints and, in combination with chemometric methods, it enables assessment of food quality and origin. The content of phenolics in wine and olive oil, and the identification of key adulterants in dietary supplements are only some of the applications of A-TEEM has found in the industry.