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The objective of this study is to characterize purebred Arab mares' milk through monitoring its physicochemical and microbiological composition during different lactation stages and to test its ability to coagulate. Sixteen purebred Arabian mares were selected among 45 mares with approximately the same foaling dates. Milk samples were collected once a week for each mare during 4 months of lactation and analysed in three replicates for physicochemical composition, nitrogen fractions, somatic cell count and total bacterial count. Coagulation assays were carried out in triplicates on fresh mare's milk using increasing doses of calf rennet, starter (Streptococcus thermophilus) and CaCl 2 . Arab mare's milk is characterized by an alkaline pH, low-fat and protein contents and high lactose content. The somatic cell and bacterial counts are very low, indicating good health status of mares. Fat and protein contents decreased as the stage of lactation progressed. However, as lactation number increased, fat level tended to increase while protein level tended to decrease. Clotting assays proved that it is possible to coagulate Arabian mare's milk using appropriate doses of calf rennet and starter, while respecting the coagulation procedures and parameters.

The aim of this study was to investigate the effect of somatic cell count (SCC) on mozzarella cheese quality. Three categories of raw milk were selected: low (SCC <115 000 cells/ml), medium (SCC=422 000 cells/ml), and high (SCC>987 000 cells/ml). Cheeses were produced on the same day of milk collection and were vacuum packed in plastic bags and analysed weekly for 60 days at cold storage (4 °C). As somatic cell count increases, casein content, casein as a percentage of true protein, lactose content, and titratable acidity decrease signifi cantly in raw milk. No signifi cant differences were observed in moisture, fat, and total protein contents among mozzarella cheese samples from the different SCC categories. However, cheese samples produced from high SCC milk had signifi cantly higher pH (6.83) compared to samples produced with low and medium SCC milk, 5.58 and 5.46, respectively. The extension of proteolysis was not signifi cant for cheese samples made from raw milk with low SCC during the fi rst 30 days of cold storage. Proteolysis levels increased signifi cantly on the 15 th storage day for cheeses made with medium and high SCC, whereas signifi cant increases were only observed on the 45 th storage day for cheeses made with low SCC.

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The present study examined the enzymes responsible for proteolysis of casein in milk. Reversed-phase HPLC was used to differentiate the peptide products, of each proteinase, soluble in 12% trichloroacetic acid and in pH 4.6 milk filtrates. Peptides produced by bacterial proteinase were less hydrophobic and eluted early in the RP-HPLC chromatogram, while peptides produced by plasmin and somatic cell proteinase were more hydrophobic and eluted later. β-caseins were preferential substrates for plasmin, whereas α s-and κ-caseins were hydrolysed to a lesser extent. Proteases from bacterial origin predominantly affected κ-casein, while ß-casein and α s-casein were less susceptible. Somatic cell proteinase degraded mainly β-casein, followed by α s-casein and κ-casein. When milk was contaminated by bacterial proteinases, chromatograms of the TCA 12% filtrate showed early peaks, while the pH 4.6 filtrate showed early and late peaks when proteolysis was caused by either plasmin, somatic cell proteinase or bacterial proteinase.