Modeling Heat Transfer and Inactivation of Escherichia coli O157:H7 in Precooked Meat Products Using FEM

M.V SANTOS,; N. ZARITZKY; A. CALIFANO

Napoles, Italia

Simposio; CIGR Section VI Third International Symposium on FOOD AND AGRICULTURAL PRODUCTS; 2007

International Commission of Agricultural Engeenering, CIGR

The presence of E.coli is linked with sanitary deficiencies and undercooking of meat products causing the Hemolytic Uremic Syndrome in humans. A mathematical model to establish time-temperature conditions in order to assure thermal inactivation of E.coli O157:H7 in black sausages was solved. The model was based on the microscopic heat transfer equation and the solution was obtained by using the finite element method. Since the products have irregular shapes, digital photographs were taken in order to obtain the contour lines of the domains. Sausages were heated in a thermostatic water-bath over a temperature range of 60 to 80ºC for model validation. Minimum processing times required to reach an inactivation value IV = 12log considering a constant water bath temperature were obtained. The solution obtained for irregular foodstuffs was compared to a finite cylinder regular geometry in order to show the differences in the thermal history and the implications to get safety conditions. Considering that  in small scale production plants water bath temperature does not maintain constant leading to an insufficient microbial lethality, the effect of the ratio between the amount of the thermally treated sausages and the heat capacity of the water bath on its temperature drop, was determined numerically solving simultaneously the macroscopic heat balance and the microscopic partial differential equations. The obtained solution could predict the new safe specifications for industrial conditions. A predictive equation for the time needed to reach an IV = 12log was obtained as a function of the initial water temperature and load ratio (kg of sausage / kg of water).