14A-35

H. CHEN, Department of Food Science, The Pennsylvania State University, 208 Borland Lab, University park, PA 16802 and R. C. Anantheswaran.

Salmonella enteritidis (SE) outbreak, associated with eggs, has been a major cause of foodborne illness. Currently, egg companies cool eggs by putting washed eggs on a pallet and storing it in a cold room. Eggs at the center of a pallet can take up to 142 hours to reach 7 °C. This slow rate of cooling may permit the multiplication of SE in eggs. Rapid cooling of eggs before packaging has been proposed as a means to control SE growth in eggs. However, rapid cooling can generate thermal stress in eggshell and promote the formation of micro-cracks. There are concerns that these micro-cracks may adversely affect eggshell strength.

The objective was to determine the effect of rapid cooling on micro-cracks development on eggshell, and eggshell strength.

Eggs were subjected to each of the four treatments, no cooling (control), multistage cooling (6 min at 0 °C and 6 min at -20 °C), liquid CO₂ cooling (6 min at -60 °C), and liquid N₂ cooling (3.5 min at -80 °C). All these cooling conditions will cool eggs to 7 °C. Cracks on eggshell and eggshell strength were determined using scanning electron microscopy and quasi-static compression test respectively.

Eggshell of non-cooled eggs had cracks of 0.4 mm wide. However, wider cracks and many offshoots were found on the eggshell of cooled eggs. Some cracks had opening as large as 1.2 mm. There were no significant differences in eggshell strength among the four treatments. The mean fracture force of eggs was about 32 N.

Our results show that though rapid cooling produces micro-cracks on eggshell, the micro-cracks formed did not affect eggshell strength. The effect of these micro-cracks on the penetration of SE into egg contents is being investigated. The results obtained will help to design a rapid cooling system.