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Determination of the Kinetic Parameters of a Time-Temperature Integrator for the Flash Pasteurization
A. Dammann, K. Schwarzer, T. Vullriede, U. Mller, J. Schneider

Processes for the thermal preservation of beverages in heat exchangers demand for validation methods, especially as performance qualification of a new plant. Particularly in the combination with aseptic filling systems reliable and precise tests are important. A chemical Time-Temperature Integrator (TTI) is expected to measure more accurate, cheaper and faster than conventional microbiological count reduction tests. The acidic hydrolysis of sucrose was investigated as a TTI. For the practical application the calibration of the chemical reaction is necessary in order to find the suitable parameters in terms of the acid and sucrose concentration. For the calibration of the TTI two methods were tested, the isothermal (two steps) and the non-isothermal (one-step) method. The latter revealed as more precise, thus it was used to explore the required kinetic parameters of the reaction. To cover the temperature range from 50 to 78 C, exemplary for the application of beer pasteurization a sugar concentration of 5 % and acid concentrations between 0.02 and 0.75mol/L were used. With respect to products with high viscosities such as beverage concentrates a 52 % sugar syrup was used. Here the reaction is faster than with 5 % sugar. According to earlier findings the activation energies of 105.09 1.07 kJ/mol (5 %) and 113.56 0.83kJ/mol (52 % sucrose) respectively were found. Of deciding importance for the application as TTI is the precise determination of the frequency factor k0 in dependency on the acid concentration. In case of both sugar concentrations a quasi-linear equation describes this correlation with high precision (R2≥0.998). Herewith earlier indistinct publications could be clarified. With the activation energy and the frequency factor the reaction rate can adjusted by changing the H+ concentration to different pasteurization intensities as appearing in practice. Because the activation energy of the thermal death of microorganisms is known to be about twice as high as of the TTI only largely, isothermal reactions can be converted in a direct manner. In non-isothermal cases the TTI slightly underestimates the death rate of microorganisms. The transfer of these findings into the practical scale and their verification shall be the subject of upcoming work.The microbial safety of beverages is of great importance for their shelf life. Pasteurization is a widely used technique to accomplish this. To describe the intensity of the pasteurization the Pasteurization Unit (PU) is used. PUs employed in the practice are often based on outdated data, for example 15-20 PU, typically used for lager beer, arise from a set of publication [1, 2, 3] dated from the early nineteen fifties. Because several factors were not determined precisely, grand safety margins were added. From todays point of view these data seem no longer to be sufficient [4]. In difference to the conventional approach, the leading objective in this paper is not the microbiologically worst case scenario but also the gentle treatment of the product and consideration of used resources. To set the pasteurization parameters time and temperature adequately, the required pasteurization units (PUre) and the effective thermal dosage (PUeff) have to be known [4]. The PUre depend on the number of the present microorganisms, their thermal death kinetics and the accepted risk of surviving microorganisms. The PUeff depend on the applied temperature and exposition time. The common but rough method to estimate the applied PUeff during pasteurization is to calculate with the average or the minimum residence time and the outlet temperature of the holding tube. Due to the effect of residence time and temperature distributions and the unconsidered heating regime in the cooling and heating zones, PUeff is not even closely known in the common use of flash pasteurizers. That is why the applied parameter setting of the pasteurization plant comprises several safety margins...

Descriptors: pasteurization, sucrose hydrolysis, Time-Temperature Integrator, kinetic parameter

BrewingScience - Monatsschrift fr Brauwissenschaft, 65 (September/October 2012), pp. 134-139