# Proteomics Analysis in Dairy Products: Cheese, a Review
## 2 Feta  
Since Ancient Greece, a cheese resembling Feta was produced, and it is believed that this cheese was Feta's ancestor. Especially a Greek historian, [PERSON] ([PERSON]; 1 st century BCE), wrote that [PERSON], whose ancestors were [PERSON] and [PERSON], father and grandfather, respectively, learnt the art of cheesemaking from the nymphs and was godsent to teach ancient Greeks how to make cheese ([PERSON], Library of History, IV 81.1-81.2) [25].  
Feta is a semi-soft, white brined, PDO traditional Greek cheese (EU L277/2002), made from ovine or mixtures of it and caprine milk (up to 30%) accompanied by starter lactic acid bacteria. The cheese is produced all over the country [26]. Feta has a mildly acidic to bitter taste, with no gas holes in the body, but with desirable mechanical openings, (i.e., little undefined holes) resulting from the mechanical pressure applied during manufacturing. Feta has low pH and is made from curds that have not been heat-treated. Dry salting is applied, draining by gravity and ripening is carried out in brine with 7-8% salt for at least 2 months. Its mean gross physicochemical composition (\(w/w\)) is the following: moisture 55%, fat-in-dry matter, 51%; protein, 17.5%; salt in moisture, 5.2%; pH, 4.6 [27]. [PERSON] [28] has reported that peptides with a hydrophobicity of \(>\)1400 cal per residue and a molecular mass \(\leq\)6000 Da are bitter. The beta-casein (b-CN) (f191-205) isolated from Feta cheese has a mean hydrophobicity of 1693 cal per residue and a molecular mass of 1669 Da. Thus, b-CN (f191-205) has likely a bitter taste, which it attributed to the bitterness of Feta [29]. Lactic acid bacteria (LAB), Enterobacteriaceaeae and coliforms are the major components of the microflora during storage of cheese. The counts of total nonstarter LAB (NSLAB) and _Lactococci_ in curd, made during spring, increased initially during ripening for 24h and then declined gradually during storage for 6 months, respectively [25].  
Milk caseins during ripening undergo hydrolysis, because of the action of proteolytic enzymes from the starters; therefore, new peptides are created, or the pristine peptides are transformed. The casein hydrolyzed by rennet combined with inorganic milk components, mostly calcium and phosphorus, create paracasein micelles [30]. The latter leads to a three-dimensional paracasein network, consisting of whey, fat and microorganisms; common in almost every cheese. Cheesemaking conditions are responsible for the pH, the concentration of the minerals and the ratio of paracasein to other cheese components. The ripening conditions in Feta are a crucial step, because of the caused changes in the paracasein network that affect all the final traits of the produced cheese. The impact of ripening is mostly seen in the protein content, which is altered by proteolysis affecting the stabilized bonds [31; 32]. The contribution of hydrophobic interactions and hydrogen bonds in the structure of Feta paracasein is significant because of the changes in paracasein-calcium interactions induced by low pH and the proteolysis pattern, thus decreasing more extensively the calcium binding sites onto the paracasein elements.