# Spectroscopic Techniques Application for Wine and Wine Byproduct Authentication
## 2 Food Spectral Print Approaches
### Fluorescence  
Fluorescence spectroscopy is a fast, simple, and highly sensitive analytical technique widely used for characterizing various compounds. The method involves exciting a sample with monochromatic light and analyzing the emitted photons from fluorophores as a function of wavelength. Each fluorophore has a distinct excitation and emission wavelength pair, at which it exhibits maximum fluorescence [70]. One significant advantage of fluorescence spectroscopy is its high sensitivity and selectivity, often surpassing other spectroscopic techniques. It is a non-destructive, non-invasive, cost-effective method with low detection limits. However, despite these benefits, fluorescence spectroscopy is less commonly utilized than vibrational spectroscopic techniques [71; 72; 73]. It is particularly effective for detecting molecules such as polyaromatic hydrocarbons and heterocycles with rigid molecular structures. Fluorescence spectroscopy has garnered significant attention in food authentication research, particularly when combined with multivariate statistical analysis [74; 75]. This combined approach has shown great potential for verifying the authenticity of various food products and beverages [76]. However, multifluorophoric food samples require more advanced measurement techniques than conventional emission or excitation spectra. Advanced fluorescence methods, such as excitation-emission matrix (EEM) fluorescence spectroscopy, synchronous fluorescence spectroscopy (SFS), and total synchronous fluorescence spectroscopy (TSFS), have been increasingly applied in food analysis [77; 78]. Fluorescence spectroscopy has shown particular promise in wine analysis due to its ability to detect polyphenols--a complex family of fluorescent molecules with diverse structures, properties, and sizes [79]. This technique provides valuable insights into molecules containing conjugated double bonds, such as phenolic acids, stilbenes, anthocyanins, fla-vanols, and tannins, influencing wine composition and quality. The concentrations and types of these compounds vary depending on grape variety, maturity, winemaking processes, and aging conditions. Additionally, wines contain other fluorescent compounds, including proteins, contributing to their spectral fingerprints [80]. Wine also contains fluorescent vitamins and amino acids. Vitamin C is present in fresh must and during fermentation, but it diminishes over time. Vitamin A is found in minimal amounts, whereas B-complex vitamins, particularly riboflavin (B2), are more abundant. In wine, riboflavin primarily exists in its free form, unlike in fruit juice and beer, where it coexists with flavin derivatives [81]. The fluorescent amino acid tryptophan has also been identified in wines [82]. Fluorescence spectra recorded from wine samples following excitation at 261 nm provide information on multiple fluorophores, effectively creating a characteristic fingerprint that enables the identification of samples [80]. The presence and composition of polyphe \begin{table}
\begin{tabular}{l l l} \hline \hline
**Wine Type** & **Application of NIR Spectroscopy** & **Ref.** \\ \hline \multirow{2}{*}{Wine from the Vinho Verde region} & Quantification of volatile compounds using FT-NIR & [65] \\  & transmission spectroscopy. & \\ \multirow{2}{*}{Red Wine} & Prediction of phenolic compounds during fermentation using & [66] \\  & NIR spectroscopy. & \\ \multirow{2}{*}{Red Wine Grapes} & Quality assessment and quantification of quality attributes & [67] \\  & like SSC, TA, and tannins. & \\ \multirow{2}{*}{Various Wines} & Classification of wines based on the aging process using NIR & [68] \\  & spectroscopy and multivariate analysis. & \\ \multirow{2}{*}{Australian Wines} & Measurement of elemental concentrations using & [69] \\  & VIS-NIR spectroscopy. & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Examples of wines in which near-infrared (NIR) spectroscopy has been applied.