Validation of mild cooking processes with target of Listeria monocytogenes inactivation to ensure food safety

This thesis investigates the use of Time Temperature Integrators (TTIs) to validate industrial cooking processes aimed to achieve a 6 logarithmic inactivation of Listeria monocytogenes, equal to a heat load of 2 min at 70 °C (P707.5 = 2) . To produce microbiological TTIs, live cells of L. monocytogenes were crossbound in alginate beads. Decimal reduction (D) values were measured in two food matrixes, meat extract and milk. D-values were compared in capillary tubes and in alginate beads. The results showed that the immobilised cells had slightly higher D-values compared with free cells in capillary tubes. Measurements in milk revealed higher D-values compared to measurements in meat extract. Alginate beads in milk showed a D58 of 4.5 min, compared to capillary tubes with a D58 of 3.7 min and alginate beads in meat extract a D58 of 1.5 min and capillary tubes a D58 of 1.0 min. Enzymatic TTIs based on inactivation of α-amylase (BAA70) were used for validation of a commercial fried fish burger production. The TTI was calibrated and had a D70 of 28.3 min and z of 6.5 °C ± 0.30 °C. The burgers were fried on both sides on a Teflon frying belt, before the burgers subsequently were heated in a continuous oven. The temperature profile calculated from a numeric model was combined with known inactivation kinetics and the residual α-amylase activity was calculated and compared to actual values of the TTIs placed in the core of the fish burgers. The results showed that α-amylase BAA70 TTIs can be used as to validate a specific minimum pasteurisation value for fried fish burgers