DEVELOPMENT OF A TIME-TEMPERATURE INTEGRATOR BASED ON ALKALINE PHOSPHATASE FOR THE EVALUATION OF MICROWAVE HEATING TECHNOLOGY

Thermal processing of liquid foods consists of the inactivation of pathogenic and spoilage microorganisms and undesirable enzymes at high temperatures. Thermal processing can be evaluated using a time-temperature integrator (TTI). An enzymatic TTI is a thermally sensitive component that, whether intrinsic or extrinsic to food, allows the quantification of the thermal process impact on the safety attribute. The aim of this work was to use alkaline phosphatase (ALP) in carbonate buffer (pH 9.6, ionic strength 88 mM) as a TTI to evaluate pasteurization processes of low viscosity liquid foods (juices, milks, nectars and beers) by its thermal inactivation (at 55.0; 60.0; 65.0 and 70.0 °C) using a focused microwave reactor (Discover Reflux, CEM, USA), at 2450 MHz, with times between 5 s and 10 min. The adapted AOAC (2016) method 979.13 was used with an indophenol standard calibration curve at concentrations up to 12.0 µg indophenol/mL of the enzyme solution to determine the reduction of activity of a 4.0 mg/L ALP solution. The activities of the samples processed in the microwave reactor were determined, according to the method, using UV-Vis spectrophotometer (700 Plus, Femto, Brazil) at 650 nm and the standard curve linear regression. 10 min at 55.0 °C reduced activity to 27.0% of the initial value. At 60.0 °C for 10 min, the activity was reduced to 7.8%. 65.0 °C for 45 s reduced activity to 9.8%. 70 °C for 5 s reduced to 3.9%. The result is consistent when compared to that of bovine milk ALP, which is completely inactivated at 72 °C for 15 s. A first order kinetic model was adjusted to the data for the practical use of this TTI.