The aim of the present work was to assess the characteristics of the paracasein of two ewe's milk cheese varieties using various concentrations of urea and EDTA to solubilise caseins and calcium. The solubilised paracasein elements were evaluated by means of RP-HPLC and AAS. For this purpose cheeses with different physical and biochemical characteristics, i.e. Feta (53.1% moisture and pH 4.32) and Graviera Kritis (33.2% moisture and pH 5.54) were analysed. Soluble calcium of Feta was 71% of total calcium much higher than the 25% in Graviera. Treatment with 4 m urea fully solubilised Feta paracasein, whereas 6 m urea was needed to solubilise caseins from Graviera. Caseins were released from both cheeses by 100 mm EDTA. Solubilisation of paracasein induced by urea or EDTA was not significantly affected (P < 0.05) by the type of cheese. Similarly to urea, EDTA induced significantly (P < 0.05) lower solubilisation of αs1-casein in Graviera than in Feta, based on αs1-cn/β-cn ratio. A great part of calcium in both cheeses was solubilised by 50 mm EDTA while the release of casein was poor, confirming the important role of types of interactions other than protein-calcium bonds in the paracasein network. Hydrophobic interactions, hydrogen bonds and electrostatic attractions, contributed substantially to the paracasein stability of both cheese types. The interactions of αs1-casein with calcium played a more significant role in Graviera cheese than in Feta. Finally, the present study demonstrated that the profile of bonds and interactions within the cheese paracasein network was dynamicly configured by the conditions of cheese manufacture.
Keywords: EDTA; Feta; Graviera Kritis; Paracasein network; cheese calcium; urea.