The viability of Listeria monocytogenes strain Brie-1 was studied in raw and heat-treated (121°C, 15 min) whole eggs, albumen, or yolks during storage at 5 and 20°C. Studies with raw eggs showed that the organism grew only in egg yolks, where initial numbers (106 cells/g) increased to 108 cells/g (generation times of 1.7 d and 2.4 h at 5 and 20°C, respectively). Cell numbers in whole eggs initially declined and then leveled off. A sharp decline in cell numbers was observed in the raw albumen (to 102 cells/g after 22 d at 5°C and to <10 after 55 h at 20°C). In contrast, the organism grew in all heat-treated egg samples. Generation times for cooked whole eggs, yolks, and albumen were 1.9, 2.3, and 2.4 d at 5°C, and 2.6, 2.6, and 3.5 h at 20°C, respectively. The rapid initial decline in populations was observed in raw albumen (pH 8.9), and after adjustments to pH 7.0 or 8.0. Numbers of surviving cells/g after 35 d at 5°C were reduced to 104, 103, and <10, at pH 7, 8, and 9 respectively. With the exception of the raw albumen, refrigerated raw and cooked eggs supported survival and growth of L. monocytogenes, and hence can serve as vehicle of transmission of listeriosis.
A simplified method for extracting androgens from avian egg yolks