# Chemometric Classification of Feta Cheese Authenticity via ATR-FTIR Spectroscopy
## 1 Introduction  
Feta cheese holds a central place in Greece's culinary tradition and remains one of the country's most widely recognized food exports. Recognized as a Protected Designation of Origin (PDO) product by the European Union (Regulation EC 1829/2002) [1], Feta is not only linked to Greece's cultural identity, but also supports a substantial part of the Greek livestock sector and contributes notably to the national agri-food economy [2]. Authentic Feta is produced exclusively from sheep's milk, or a mixture of sheep's and up to 30% goat's milk, sourced from animals raised in specific regions of Greece under defined feeding and husbandry conditions [3]. Its distinctive profile results from the specificity of the raw materials and the traditional methods of production and maturation, which impart characteristic organoleptic and physicochemical properties. According to recent compositional studies on commercial PDO Feta products, the cheese typically contains 45-60% moisture, 21-25% fat (in total weight), and 14-50% protein, depending on milk origin and processing conditions [4; 5]. The lipid fraction of Feta consists predominantly of short- and medium-chain fatty acids, while its protein matrix includes caseins and whey proteins, whose structure is influenced by enzymatic coagulation and brine aging. Additionally, the salt content typically exceeds 2.5%, contributing both to microbial stability and to its distinct sensory profile. The differentiation of white brined cheeses, such as Greek Feta and similar products made from cow's or goat's milk, is significant for consumer protection as well as for ensuring product quality and regulatory compliance. PDO cheeses like Feta carry a high added value and are subject to strict compositional and production standards [6]. Adulteration with lower-cost raw materials not only compromises product quality but also undermines consumer trust and places compliant producers at a competitive disadvantage. Economically, the global cost of food fraud has been estimated to range from USD 10 to 65 billion per year, affecting both consumer confidence and supply chain integrity [7]. Within the European Union, the sales value of GI-protected cheeses such as Feta was estimated at EUR 6.3 billion in 2010, with an annual consumer loss of approximately EUR 644.7 million attributed to GI infringement [8]. These data highlight the pressing need for reliable, efficient, and field-deployable methods to verify authenticity and support regulatory enforcement. Recent research has shown that despite the strict regulatory framework governing its production, Feta remains susceptible to adulteration, most notably through the inclusion of cow's milk or vegetable fats. An investigation by [PERSON], [PERSON], and [PERSON] (2016) reported that 14 out of 34 samples were found to be adulterated with cow's milk [9]. These practices aim to reduce production costs but significantly compromise the product's quality, nutritional value, and authenticity, while undermining consumer trust and disadvantage compliant producers. In recent years, the scientific community has underscored the importance of authenticating PDO products, particularly Feta, using advanced analytical techniques. Studies such as those by [PERSON] et al. (2024) and [PERSON] et al. (2013) have employed molecular methods (e.g., Polymerase Chain Reaction, High-Resolution Melting) to detect bovine DNA in Feta samples [10; 11]. Other research has focused on spectroscopic approaches (e.g., MALDI-TOF-MS, NIR) for purposes of authentication and quality control [12]. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy has emerged as a promising tool for the analysis of dairy products, offering a rapid, non-destructive, and cost-effective solution [13]. Several analytical platforms have been explored for this purpose, each with distinct strengths and limitations.