Characterization and Discrimination of Pure Standards of Phenolic Compounds Using FTIR Spectroscopy in the Terahertz Range

Phenolic compounds (PCs) are bioactive molecules synthesized by plants and recognized for their antioxidant, antimicrobial, and anti-inflammatory properties. Traditional methods for their analysis, such as HPLC or GC, are time-consuming and costly, which motivates the exploration of faster and non-destructive alternatives. This study investigates the potential of Fourier Transform Infrared (FTIR) spectroscopy in the Terahertz (THz) range for the identification and discrimination of PCs. Fifty-five pure standards, including phenolic acids and flavonoids, were analyzed using an FTIR spectrometer equipped with an Attenuated Total Reflectance (ATR) accessory. Measurements were performed at room temperature with 2-4 replicates. Repeatability and time reproducibility were good overall but decreased towards lower frequencies. Partial Least Squares Discriminant Analysis (PLS-DA) was applied as an exploratory tool to assess the global spectral variability among PCs and to determine whether their class or family was associated with systematic spectral features. The models achieved moderate to high accuracy in distinguishing between phenolic acids, flavonoids, and their subclasses. This study demonstrates the ability of THz spectroscopy to discriminate pure phenolic compounds despite their complex spectral profiles and represents a first step toward its application in real food products. Future work should address the limited sensitivity of FTIR spectroscopy for trace detection and the high absorption of water in the FIR-THz range, through experiments on dry mixtures of pure PCs and model food supplements to establish suitable conditions for food analysis.