The manufacture of Ras cheese from gamma irradiated milk

Abstract

Cheese milk exposed to gamma irradiation at a dose of 0·5 Mrad was used in the manufacture of Ras cheese. Quality and ripening of cheese made from irradiated milk were compared with those of cheese made from heat-treated milk. Gamma irradiation of cheese milk reduced the total bacterial count and spore formers by 98·98% and 95·77%, respectively, and eliminated the coliform and pathogenic bacteria. This treatment slightly increased the acid and peroxide values of milk fat, as well as the time required for complete coagulation of milk. An oxidized flavour in the fresh and 1-month-old gamma-irradiated milk (GIM) cheese disappeared during ripening. At the end of ripening, GIM cheese had a better consistency and increased flavour compared with cheese made from heated milk. Ras cheese made from GIM differed little in gross chemical composition but contained higher concentrations of soluble nitrogen compounds and of Free Fatty Acids than the control. Irradiation had a stimulating effect on the total, proteolytic and lipolytic bacterial counts during cheese ripening.