232 International Food Congress‐Novel Approaches in Food Industry, MAY 26‐29, 2011 Integrated lethality for the non-ideal flow of a pseudoplastic liquid food V. Kechichian, C.C. Tadini, J.A.W. Gut * University of Sao Paulo, Escola Politecnica, Dept of Chemical Engineering, Sao Paulo, Brazil jorgewgut@usp.br Abstract The analysis of the continuous thermal processing of a liquid food can be compromised by the common assumptions of isothermal ideal flow, instant heating and cooling steps and minimum residence time approach. In order to optimize safety, sensorial and nutritional attributes of the food, the thermal process should be modeled considering flow, heat transfer and kinetics principles. In this work, the thermal processing of a pseudoplastic (power-law) fluid in a tubular system is modeled taking into account the effective heat diffusion and mass diffusion in laminar flow, the reaction kinetics for microorganism or enzyme inactivation and quality attribute changes, as well as heat losses to the ambient. The model comprises differential equations for heat and mass balances applied to the heating and cooling sections (double-pipe heat exchangers) and the holding tube. Axial and radial components were discretized using finite difference methods and the model was solved using gPROMS (PSE). Main simulation results were the radial and axial distributions of temperature and concentration of microorganisms. The axial distribution of the integrated lethality (S-value) was also obtained for process evaluation. The model was successfully applied for the study of the pasteurization of soursop juice and the results are presented and discussed. Introduction The continuous thermal processing of liquid foods was developed to solve problems observed in the batch processing, such as low rate of heat penetration and long processing time to achieve the correct temperature needed to ensure the required lethality. The main advantages of continuous thermal processing, when compared to discontinuous processing, are: increasing production capacity, reduction of energy consumption and improvement in the sensorial characteristics of the final product due to lower processing temperature and time (Torres and Oliveira, 1998). Pseudoplastic liquid foods like fruit juices and purées have a complex flow behavior and are often processed in heat exchangers in laminar flow. This way, the velocity profile, the residence time distribution and the temperature profile, regarding axial and radial domains, need to be considered for proper lethality evaluation and design of the thermal process (Gratão, 2006). Despite these flow characteristics, the assumptions that are often used for the process design are: isothermal plug flow at the maximum velocity (minimum residence time), instant heating and cooling (the lethality takes place only in the holding tube) and no mass or heat dispersions or heat losses to the ambient. Since these assumptions lead to over-processing, they can guarantee product safety but undesired nutritional and sensorial changes of the product may occur (Jung and Fryer, 1999). Nowadays, the demand for processed foods goes beyond basic requirements of food safety and assurance of shelf-life stability. Recent studies have been conducted to determine the most appropriate conditions of thermal processing in order to preserve sensorial and nutritional characteristics of the food product (Ditchfield et al., 2006; Awuah et al., 2007). The objective of this work was to develop and test a mathematical model to simulate the continuous thermal processing of a pseudoplastic liquid food under non-ideal laminar flow in order to determine the integrated lethality and the temperature profile.