# Chemometric Classification of Feta Cheese Authenticity via ATR-FTIR Spectroscopy
## 1 Introduction
Compared to molecular techniques such as PCR or HRM analysis, which require DNA extraction, species-specific primers, and thermal cycling, ATR-FTIR is reagent-free, non-destructive, and involves minimal sample preparation. While MALDI-TOF-MS offers high-resolution identification of peptides and proteins and is widely used in microbiological analysis, it is less suitable for non-biological adulterants in complex food matrices and involves expensive instrumentation and trained personnel. NIR spectroscopy, on the other hand, enables fast and non-invasive screening with excellent repeatability but is less specific in heterogeneous samples, particularly when detecting low levels of adulteration [14]. In contrast, ATR-FTIR provides a favorable balance between specificity, speed, and practicality, making it particularly attractive for routine authenticity screening in quality assurance workflows [15]. Its operational simplicity, low per-sample cost, and potential for portable deployment further enhance its applicability. With its ability to detect characteristic absorption spectra of compounds such as proteins, lipids, and carbohydrates, ATR-FTIR provides a chemical fingerprint of a sample's composition. When combined with chemometric methods, it enables classification and quantitative estimation of adulterants--even at low concentrations [16]. Similar applications of ATR-FTIR spectroscopy have demonstrated successful performance in distinguishing PDO mozzarella [6] and in discriminating cheeses derived from different milk species [17], thereby supporting the reliability of this methodology across a broad range of white brined cheese production contexts. This spectroscopic technique has also been successfully applied to other cheese types, including Italian Pecorino [18], Turkish white cheese [19], and Halloumi [20], but existing studies on Feta have largely been limited to general compositional analysis or microbiological profiling, such as those by [PERSON] et al. (2021), [PERSON] et al. (2021), and [PERSON] et al. (2016), without systematically addressing adulteration or developing robust chemometric authenticity models [21; 22; 23]. Despite its potential, ATR-FTIR spectroscopy has not been systematically applied to the authentication of PDO Feta. To our knowledge there are no previous studies that explored its use for reliably distinguishing authentic Feta from cheeses made with cow's milk or other non-compliant ingredients. This highlights a clear gap in applied research focused on classification-based approaches for authenticity assessment, using spectral data and chemometric tools. Based on this context, the present study was designed around the following theoretical framework: (1) ATR-FTIR spectroscopy can capture chemical fingerprint information relevant to cheese composition, including signals from lipids, proteins, and carbohydrates; (2) chemometric classification models (PCA-LDA and PLS-DA) can effectively discriminate between complex spectral profiles from authentic and non-authentic cheese samples; and (3) freeze-drying and spectral preprocessing enhance spectral resolution and model performance. These assumptions guided the development and evaluation of a classification pipeline for the authentication of PDO Feta cheese.