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Evaluation of the Acidic Sucrose Hydrolysis as Time-Temperature Integrator in Flash Pasteurizers
A. Dammann, K. Schwarzer, U. Mller and J. Schneider

In the practice of flash pasteurization, the applied heat load is not exactly known. It is rather estimated by measuring the holding tube outlet temperature and the flow rate (theoretical mean holding time). Microbiological methods, such as the Count Reduction Test (CRT), include certain disadvantages and basic unavoidable inaccuracies. A chemical reaction, the acidic sucrose hydrolysis, was investigated as a Time-Temperature Integrator (TTI) for the determination of the heat load expressed as Pasteurization Units (PU). For this purpose, the reaction was already calibrated as reported in a prior article [1]. Here the application and verification in terms of a comparative plausibility test of the TTI in a semi-technical scale are presented. For the TTI test, the conversion rate of the reaction had to be adjusted with a sufficient acid concentration, which can be calculated with the help of the previous calibration. The acidic sucrose solution is pasteurized under realistic conditions. The conversion ratio is mathematically transposed into a statistical figure, the effective temperature (ThetaTTI). The effective PU can then be derived from the ThetaTTI and the residence time. This TTI test was performed at four different temperature levels using three different target residence times, 5-fold respectively. The resulting effective temperatures were compared with the measurements of thermocouples (inlet and outlet of the holding tube). The results indicate that the TTI provides plausible results. In the following step, the TTI was compared with a microbiological Count Reduction Test. Lactobacillus hilgardii was chosen as the test microorganism, therefore, thermal death kinetics of L. hilgardii were determined in terms of the D60 C-value of 0.75 min and a z-value of 5.4 C. Both methods, the TTI and the CRT, were performed under the same process conditions. The comparison with the measurements of the temperature probes in the holding tube revealed a significant higher reliability of the TTI test.

Descriptors: flash pasteurization, Time-Temperature Integrator, residence time distribution, Count Reduction Test, D- and z-values, Lactobacillus hilgardii

BrewingScience - Monatsschrift fr Brauwissenschaft, 67 (January/February 2014), pp. 10-17