# Spectroscopic Techniques Application for Wine and Wine Byproduct Authentication
## 2 Food Spectral Print Approaches
### Infrared (IR) Spectroscopy
#### 2.2.2 Near-Infrared (NIR) Spectroscopy  
NIR spectroscopy measures a sample's absorption of near-infrared light. The absorption bands result from overtones and combination vibrations of molecular bonds, primarily involving C-H, N-H, and O-H groups [58; 59], as shown in Figure 3. The technique uses spectrometers that can be miniaturized for various applications. Recent advancements in instrumentation and spectral analysis methods, such as spectral image processing and quantum chemical calculations, have enhanced their applicability [60; 61]. NIR spectroscopy often requires multivariate calibration algorithms to interpret the spectral data. NIR spectra are composed of broad and overlapping bands, making direct interpretation of the data difficult. Therefore, it is common to use multivariate calibration algorithms, such as PLS regression and PCA, to extract relevant information and build reliable predictive models. These statistical methods enable the correlation of spectral data with sample attributes of interest, thereby increasing the accuracy and robustness of NIR analyses [61]. Chemometrics is commonly used to model the spectral response to the chemical or physical properties of the samples [59; 62]. NIR is a powerful analytical technique for authenticating wine and its byproducts. It offers a rapid, non-destructive, and cost-effective method for analyzing various quality parameters and ensuring the authenticity of wine products. This technique is often combined with chemometric methods to enhance its effectiveness. NIR spectroscopy, often combined with visible spectroscopy (Vis-NIR), has been demonstrated to effectively detect quality parameters, including total acid, total sugar, and alcohol content, in wines. Advanced algorithms, such as ant colony optimization (ACO), enhance the prediction performance of these parameters, rendering them a reliable method for quality assessment [63]. This technique, when combined with chemometrics, has been successfully applied to authenticate high-quality wine viegears with a PDO. This method demonstrated a high prediction accuracy, making it a valuable tool for preventing adulteration and ensuring brand protection [64]. It can also quantify volatile compounds in wines, such as those found in wines from the Vinho Verde region, which are traditionally determined by gas chromatography. The technique offers a promising, rapid tool for quantifying these compounds, with high coefficients of determination indicating its reliability [65]. NIR spectroscopy is often used in conjunction with other techniques, such as MIR spectroscopy, electronic tongue (E-tongue), and headspace-solid-phase microextraction-GC-MS (HS-SPME-GC-MS), for comprehensive wine authentication. This integrative approach allows for a more robust differentiation of wines, particularly in identifying geographical origins and preventing adulteration [58]. It has been proven to be very reliable when compared to other techniques. NIR spectroscopy, UV-Vis spectroscopy, and artificial noses and tongues have been compared for their effectiveness in characterizing Italian red wines. These techniques, when combined with chemometric pattern recognition, provide a comprehensive fingerprinting method for distinguishing wine samples based on grape variety [29]. Despite its advantages, implementing NIR spectroscopy in routine wine analysis presents several challenges, including a lack of understanding of the technology and a high degree of dependence on mathematical models. Addressing these issues is crucial for the broader adoption of this technology in the wine industry [34]. Thus, the continuous development of NIR spectroscopy and its integration with chemometrics holds promise for wider applications in wine authentication. As technology advances, it is expected to become an even more integral part of ensuring wine quality and authenticity in the global market [4]. Table 4 presents examples of wines where NIR spectroscopy has been applied, along with the following references.