# Spectroscopic Techniques Application for Wine and Wine Byproduct Authentication
## 2 Food Spectral Print Approaches
### Infrared (IR) Spectroscopy  
IR spectroscopy is an analytical technique used to identify and study molecular structures by analyzing their interactions with infrared light. It primarily detects the vibrational modes of chemical bonds within a molecule. When infrared light is passed through a sample, molecules absorb specific wavelengths corresponding to their vibrational frequencies. The absorbed energy causes bond vibrations, such as stretching, bending, and twisting. Each type of chemical bond (C-H, C=O, O-H, etc.) absorbs IR radiation at characteristic frequencies. A detector measures the transmitted or reflected light, producing an IR spectrum that serves as a molecular fingerprint. As a secondary technique, IR spectroscopy often relies on calibration models for quantification and detects bond vibrations caused by dipole changes. In the food industry, NIR and MIR spectroscopy are primarily employed for various applications [41].  
In the analytical procedure, a thermal source, such as a Global or Nernst glower, emits infrared radiation within the range of 4000 to 400 cm\({}^{-1}\). This IR beam either passes through or reflects off the sample, which can be in solid, liquid, or gas form. The sample absorbs IR light at specific frequencies, which excites various vibrational modes, including stretching, bending, twisting, and wagging.  
A detector, such as a pyroelectric, thermocouple, or photoconductive detector, measures the intensity of the transmitted or reflected IR light. The instrument then generates an IR spectrum, plotting absorbance or transmittance against wavenumber. The resulting peaks in the spectrum correspond to specific bond vibrations, facilitating the identification of the molecules present in the sample [41].  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Wine Type/Region** & **Application of UV-Vis Spectroscopy** & **Ref.** \\ \hline Spanish Wine Vinegars & Used for the authentication and discrimination of wine vinegars by developing classification models. & [24] \\ Red Wines (DO Rias Baixas and DO Ribeira Sacra, Spain) & Determination of polyphenolic compounds using UV–Vis–NIR spectroscopy and chemometrics tools. & [33] \\ Sardinian Wines (Vermentino and Cannonau) & Characterization of polyphenolic fractions during winemaking using UV–Vis and FTIR spectroscopy. & [36] \\ Industrial and Commercial Wines & Monitoring phenolic composition and levels during winemaking using UV–Vis spectroscopy. & [31] \\ Red Wines (Austrian Cultivars) & Discrimination of wine cultivars using UV–Vis spectroscopy of phenolic extracts. & [38] \\ Chinese Rice Wines & Classification of wines from different geographical origins using UV–Vis spectroscopy. & [39] \\ Chinese Cabernet Sauvignon Wines & Geographical classification using data fusion of UV–Vis and synchronous fluorescence spectroscopies. & [40] \\ Red Wines & Quantification of polyphenols using UV–Vis and FTIR spectroscopy with chemometrics. & [32] \\ \hline \hline \end{tabular}
\end{table}
Table 2: UV–Vis spectroscopy techniques apply to wine and its byproducts.