Golfo Moatsou

Effect of draining temperature on the biochemical characteristics of Feta cheese

Two different draining temperatures, 15 and 21°C were applied to five Feta cheese curds made with different starters, containing mesophilic or thermophilic strains or mixtures of them. After 20 h of draining, the pH of curds made with thermophilic starters ranged from 5.28 to 5.49. The draining temperature significantly affected (P<0.05) the pH and the total solids of the cheeses. The inclusion of whey proteins in the cheese curd due to the insufficient draining of cheeses at 15°C, resulted in higher water-soluble nitrogen (WSN), as % of total nitrogen content. Free amino acid contents were significantly affected (P<0.05) by the draining temperature and by the presence of thermophilic lactobacilli in the starter mixture. Draining temperature also significantly affected (P<0.05) residual αs- and β-casein and the RP-HPLC profiles of the WSN. The C2:0 to C8:0 free fatty acids, hardness (kg) and fracturability (kg), as well as the total organoleptic scores, were significantly (P<0.05) higher in feta drained at 21°C.

Assessment of heat treatment of various types of milk.

Raw milk (RM), reconstituted condensed milk (CM) and three types of reconstituted milk powders (SMPs) were heated indirectly at 80-140°C for 4 s. Native β-lactoglobulin after 90°C treatment of RM was 1132±167 mg/L but no reliable quantities were estimated at temperatures >100°C, whereas 218±43 mg/L residual α-lactalbumin were found at 130°C. Average lactulose contents from 51 to 1549 mg/L were detected at ⩾100°C; average furosine was 1.9 and 126.5 mg/L in raw and 140°C treated milks respectively. The behaviour of heated CM was similar to that of heated RM except for higher furosine concentration. Reconstituted SMPs contained high quantities of lactulose and furosine, the ratio of which was lower than in similarly treated RM. Among the market milks analysed, the group of high-pasteurised milks was highly variable; i.e. native β-lactoglobulin was 69-2831 mg/L, lactulose 0-824 mg/L and furosine 3.3-68.8 mg/L.

Effect of high-pressure treatment at various temperatures on indigenous proteolytic enzymes and whey protein denaturation in bovine milk

The objective of the present study was to determine the effect of high pressure (HP) processing (200, 450 and 650 MPa) at various temperatures (20, 40 and 55 degrees C) on the total plasmin plus plasminogen-derived activity (PL), plasminogen activator(s) (PA) and cathepsin D activities and on denaturation of major whey proteins in bovine milk. Data indicated that transfer of both PL and PA from the casein micelles to milk serum occurred at all pressures utilized at room temperature (20 degrees C). In addition to the transfer of PL and PA from micelles, there were reductions in activities of PL (16-18%) and PA (38-62%) for the pressures 450 and 650 MPa, at room temperature. There were synergistic negative effects between pressure and temperature on residual PL activity at 450 and 650 MPa and on residual PA activity only at 450 MPa. Cathepsin D activity in the acid whey from HP-treated milk was in general baroresistant at room temperature. The residual activity of cathepsin D decreased significantly at 650 MPa and 40 degrees C and at the pressures 450 and 650 MPa at 55 degrees C. Synergistic negative effects on the amount of native beta-lactoglobulin were observed at 450 and 650 MPa and on the amount of native alpha-lactalbumin at 650 MPa. There were significant correlations between enzymatic activities (PL, PA and cathepsin D) and the residual native beta-lactoglobulin and alpha-lactalbumin in bovine milk. In conclusion, HP significantly affected the activity of indigenous proteolytic enzymes and whey protein denaturation in bovine milk. Reduction in activity of indigenous enzymes (PL, PA and cathepsin D) and transfer of PL and PA from the casein to milk serum induced by HP is expected to have a profound effect on cheese yield, proteolysis during cheese ripening and quality of UHT milk during storage.

Nitrogenous fractions during the manufacture of whey protein concentrates from Feta cheese whey

Abstract Samples taken from different manufacturing stages of Feta cheese whey protein concentrates (WPCs), with 65 and 35% total protein content, were analyzed by chemical methods and by reversed-phase HPLC and by size-exclusion chromatography. Mean total protein content of Feta cheese whey was 1.37%. 22% of total nitrogen (TN) was non-protein N (NPN) and 12% was proteose–peptone N (PPN). The mean native N (NN), NPN and PPN percentages of WPC 65 and 35%, were 63 and 71%, 10 and 14%, 0.08 and 0.08%, respectively. According to reversed-phase HPLC data, the percentages of β -Lg and α -La and their ratio were high; 56.5 and 59% of native proteins of whey and of WPC powders, respectively, were β -Lg. The respective α -La percentages were 13.1 and 14.1% and the respective caseino-macropeptide (CMP) percentages were 12.9 and 15.3%. Apart from ultrafiltration, the most critical stage for nitrogenous fraction composition was the evaporation process before spray drying.

Detection of caprine casein in ovine Halloumi cheese

Abstract Halloumi cheeses were made from different mixtures of ovine and caprine milk, and in some cases from bovine milk also. The casein fractions of the cheese were analyzed for para-κ-casein using cation-exchange high performance liquid chromatography for para-κ-casein. The detection of caprine casein in cheese was based on the retention times and on the peak areas of caprine and ovine para-κ-caseins. Bovine para-κ-casein in Halloumi cheese could not be detected. The detection limit of caprine milk in the total of ovine and caprine cheese milk was 5%, w/w. The estimated percentages of caprine para-κ-casein detected in the cheese were lower than the corresponding percentages of caprine milk in the cheese milk. However, the levels of caprine para-κ-casein in the cheese were significantly correlated with the level of caprine milk in the ovine-caprine milk mixture used for cheese manufacture.

Effect of supplementation of brine with calcium on the Feta cheese ripening

Feta blocks ripened in plain or calcium-supplemented brine were analysed with respect to biochemical characteristics, proteolysis and inorganic fractions; moreover, the inorganic and N content of the respective brines was estimated. The acidification of Feta in supplemented brine was faster, the moisture content was lower, secondary proteolysis was more extended, and the organoleptic scores were higher compared to control Feta ripened in plain brine. The TCASN fraction of cheeses contributed more than that of WSN to the N enrichment of brine. It was concluded that calcium supplementation of the brine retarded the diffusion of cheese N and Ca into the brine.

The effect of addition of skimmed milk on the characteristics of Myzithra cheeses.

Myzithra cheese is a traditional Greek whey cheese. Three types of Myzithra cheese were produced from A: 100% whey; B: 90% whey+10% ovine milk and C: 90% whey+10% skimmed ovine milk and were evaluated. The addition of skimmed milk to whey resulted in a new dietary product, containing 9.24% fat, with good quality, a harder texture and higher levels of ash, Ca, Mg and K than those of experimental cheeses A and B. Electrophoretic patterns and HPLC chromatograms of the proteins of Myzithra cheeses revealed the presence or not of αs-CN to the whey cheeses. In addition, SDS-electrophoresis of proteins under special preparation of samples permitted for first time the separation of whey-cheese protein (WP) components that had been denatured during cooking of the whey.

Preparation of Functional Yogurt Enriched With Olive-Derived Products

With the aim of producing novel functional foods, we investigated the incorporation of oleuropein either in pure form or in the form of dried olive leaf infusion into cows milk and yogurt. Oleuropein is the main bioactive ingredient of olive leaf extract which has been recognized by the European Medicines Agency as an official herbal drug displaying a broad variety of health beneficial properties. Oleuropein was found to be stable during heat treatment, fermentation, and storage. Physicochemical, microbiological, structural, and sensory properties were evaluated throughout cold storage. The yogurt exhibited growth of lactic acid bacteria, pH, and titratable acidity similar to the control and was characterized by improved firmness, viscosity, and water-holding capacity. The novel product displayed acceptable taste, color, and texture similar to the conventional ones. Olive leaf extract or pure oleuropein can be added as active ingredients in milk and yogurt preparations to provide novel functional dairy products.

Comparative study of the paracasein fraction of two ewe's milk cheese varieties.

The aim of the present work was to assess the characteristics of the paracasein of two ewes 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.