Effects of egg yolk and salt on Micrococcaceae heat resistance

The heat resistance and growth possibilities of various members of the Micrococcaceae in egg yolk and egg yolk with added salt were determined. Egg yolk alone protected members of the Micrococcaceae considerably against heat. Whereas in water Staphylococcus aureus S6 had a decimal reduction time (D) value of 66 s at 55 degrees C, its D value in egg yolk at the same temperature was 246 s. In salted egg yolk (water activity, 0.95), S. aureus S6 had a D value of 180 s at 66 degrees C and was largely inactivated during the pasteurization processes currently applied. Micrococcus saprophyticus and S. epidermidis (D value of each under the same conditions, 390 s) could survive such treatments to a certain extent and can thus spoil commercial egg yolk.