17H-17 |
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G. CHEN1, C. M. Corvalan2, and O. H. Campanella1. (1) Dept. of Agricultural & Biological Engineering, Purdue Univ., 1146 Agricultural & Biological Engineering Bldg., West Lafayette, IN 47907-1146, (2) Dept. of Food Science, Purdue Univ., 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 Traditionally, microbial inactivation is assumed to follow first-order kinetics, which theoretically produces log-linear survival curves. However experimental survival curves with downward and upward concavity are frequently observed. It has been shown that many nonlinear survival curves can be described by a power law model which involves a so called "memory effect", i.e., it describes the dependence of the momentary microbial death rate on previous heating history. A general fractional model, which has been shown to perform much better than the first-order kinetics, has been proposed to describe non-isothermal treatments. The objective of this study was to develop a method based on the fractional model to determine the relationship of the survival parameters with temperature from non-isothermal microbial survival data. The survival parameters were obtained from non-isothermal survival curves using numerical and non-regression methods. For isothermal semi logarithmic linear survival curves there is an analytical solution to solve this problem. However, for concave curves more elaborated but workable numerical calculation procedure is required. For validation purposes survival parameters were also obtained from a series of isothermal survival curves. It was shown that these two methods provided very close estimations of the survival parameters. The non-isothermal method has two advantages: 1) it is less time consuming because only one non-isothermal survival curve is needed; 2) it enables the determination of survival parameters in the actual medium of interest. Hence, the inherent limitations of the isothermal method (e.g., it does not work for viscous media or liquids with suspended particles) are avoided.
Session 17H, Food Engineering: Thermal processes
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