Evolution of proteolysis in Urfa cheese made from ewe's milk by wild type starter culture systems

Abstract

The evolution of proteolysis in Urfa cheese made from ewe's milk by using various combinations of wild-type strains of Lactococcus lactis (strain 1B4), Lactococcus garvieae (strain IMAU 50157), Enterococcus faecalis (strain KLDSO.0341), Enterococcus faecium (strain ATCC 19434) and Enterococcus durans (strain IMAU 60200) was monitored for 180 days. The strains used in the study were isolated from traditional raw ewe's milk Urfa cheese and characterized by phenotypic and genotypic studies previously. Three different combinations of the strains were employed in the manufacture of cheeses from pasteurized milk. These are: cheese A (strains 1B4+ATCC 19434+IMAU 50157), cheese B (strains 1B4+IMAU 60200+ATCC 1934) and cheese C (strains ATCC 19434+1B4+IMAU 50157+IMAU 60200+KLDSO.0341). The control cheese (cheese D) was produced from raw ewe's milk without starter culture. Proteolysis in the cheeses was evaluated using urea-PAGE of pH 4.6-insoluble and RP-HPLC of both 70% ethanol-insoluble (EtOH-i) and ethanol-soluble (EtOH-s) nitrogen fractions. The variations in water soluble nitrogen (WSN) and trichloroacetic acid-soluble nitrogen (TCA-SN) were also monitored during ripening as well as gross compositions of the cheeses. Results indicated that the degradation of casein fractions were faster in the cheeses A, B and C than the control. The peptide profiles of 70% EtOH-i and EtOH-s nitrogen of the cheeses A, B and C were close to each other but far more extensive than the control cheese. The proteolytic capacities of the strains employed in the cheeses A, B and C were superior to that of raw milk flora. To conclude, any of the combinations of the wild-type strains could be used in the production of Urfa cheese from pasteurized ewe's milk, as long as the safe use of enterococcal strains is assured.