###### Abstract  
The inactivation kinetics of an \(\alpha\)-amylase enzymatic time-temperature integrator (TTI) from _Bacillus subtilis_ (BAA) under continuous-flow microwave (MW) and conventional heating conditions were evaluated and compared in this study. The TTI dispersed in a buffer solution (pH 5.0 to 6.9) at 20 \({}^{\circ}\)C initially, and it was continuously circulated through two helical coils connected in a series for heating. The two coils were positioned in two domestic microwave ovens (2450 MHz and 1000 W nominal capacity each) and connected by a short tube. The sample flow rates were  
surface. Microwave (MW) heating could provide an alternative for the continuous pasteurization of liquid food products. Microwaves heat by a different mechanism compared to conventional thermal heating: the heat is generated internally due to molecular vibrations of dipole and ionic components in response to the changing electric fields created by the magnetrons. The dipole materials undergo flip-flop rotations, while the ionic components undergo a back-and-forth motion. With domestic microwaves operating at 2450 MHz, these oscillations could occur millions of times in a second, creating kinetic motion and internal friction heating. The microwaves pass through the relatively cooler heat exchanger surface and the product is heated internally, and, as a result, the fouling problem is largely eliminated. The greater penetration depth and the faster heating rates associated with microwave heating have been recognized as potential factors to improve the retention of thermo-labile constituents in liquid foods, such as milk and fruit juices [1; 2]. A potential advantage of continuous-flow sterilization or pasteurization of fluid food over conventional sterilization methods for cannot foods is also that product quality can be improved due to higher nutrient retention. Several studies have reported the successful microwave pasteurization of milk [3; 4]. Microwave inactivation of enzymes and microorganisms in fruit juices have also been studied [5]. [PERSON] and [PERSON] [6; 7; 8; 9] applied microwave heating for inactivation of pectin methyl esterase (PME) in orange juice and the destruction of spoilage microorganisms (_S. cerevisiae_ and _L. plantarum_), and found that the inactivation/destruction followed typical first-order reaction kinetics that showed a linear destruction rate on a logarithmic plot of residual activity/survivors vs. residence times. In these studies, microwave heating was shown to inactivate the enzyme and destroy the microorganisms by an order of magnitude faster than conventional thermal heating. However, the two selected strains were very sensitive to microwave heating and rapid destruction was achieved at a relatively low temperature and short heating times, and, as a result, these are not suitable for high-temperature studies. A time-temperature indicator (TTI) is defined as a small, inexpensive device that is time- and temperature-dependent and easily measurable, and irreversible change can be correlated to the changes of a target attribute of a food undergoing the same variable temperature exposure. Therefore, a TTI with high thermo-stability is desired if one were to use enzymatic inactivation as a high temperature-time integrator (TTI). Several studies have been carried out to evaluate the effect of microwave heating on biological and chemical systems using different approaches, experimental designs, and techniques. Various strains of microorganisms and enzymes have been employed in these studies. Some studies [10; 11; 12] have associated the microwave effects to be mainly due to the thermal effects of the dipolar molecular friction heating. Other studies [6; 7; 8; 9; 13; 14; 15] have observed the non-thermal or enhanced thermal effects of microwaves. [PERSON] et al. [16] have explored the possibility of non-thermal effects of microwave heating on the inactivation of wheat germ lipase, and they found microwave inactivation to be more effective than the conventional kind, while [PERSON] et al.