14A-42

S. F. ALMONACID¹, R. SIMPSON², P. Nunez, O. Saavedra, and L. Borzone. (1) Department of Processes, Chemical, Biotechnological and Environmental, Universidad Tecnica Federico Santa Maria, Ave Espana 1680, P.O. Box 110-V, Valparaiso, Chile, (2) Food Egineering Department, Universidad Catolica de Valparaiso, Waddington 716, Valparaiso, Chile

Eggs and eggs preparations are important vehicles for Salmonella Enteritidis (SE) infections. The influence of time-temperature becomes important when the presence of this organism is found in commercial shell eggs. In Chile eggs refrigeration is not mandatory, resulting in an imminent risk of public health.

The objective of this study was to develop a mathematical model and computer software for the estimation of time-temperature at different eggs locations under real or simulated ambient temperature.

The Finite Element technique was used to solve the heat transfer model because of shape and the complex nature of eggs system. The local heat transfer coefficient (h) was determined for an acrylic egg, with known thermophysical properties. The mathematical model was solved using the Macsyma Pdese software, therefore, h values were estimated by optimization from experimental data. The same procedure was used for real eggs, but this time, h values were known and thermophysical properties were the unknowns (Thermal conductivity (K) and Apparent volumetric specific heat (ROCp)). A final experiment was done to determine the global heat transfer coefficient (Uc) considering the egg in a typical cardboard box.

Good agreement was found between experimental and theoretical data. h were in the range of 1.5 to 4.4 [W/m2 °K] respectively, with mean temperature error of 0.19°C. K were 0.63 [W/m K] for egg white and 0.45 [W/m K] for yolk. ROCp were 3214 [KJ/m3 K] and 3053 [KJ/m3 K] for egg white and yolk respectively with mean temperature error of 0.32°C. Uc was estimated to be 8 [W/m2 K] under refrigeration conditions and 2.4 [W/m2 K] for stagnant air conditions, with a mean temperature error of 0.24°C.

Under Chilean situation the control against growth and proliferation of SE lies upon time-temperature histories of eggs during storage and transportation.

Key words: Egg refrigeration, Math modeling, Salmonella risk