## 3 Results
### Decimal Reduction Time Comparisons  
The D-values obtained and corrected from the experimental survivor data at different temperatures and pHs are shown in Table 2. D-values from the conventional batch system and microwave heating are summarized, which provides some very interesting comparisons between the enzyme inactivation in the two heating systems. The D-values under the microwave heating condition ranged from 16 s to 5 s at pH 5.0 between 65 and 75 \({}^{\circ}\)C, from 27 to 6 s at pH 5.6 between 60 and 80 \({}^{\circ}\)C, and from 89 to 22 s at pH 6.0 between 70 and 85 \({}^{\circ}\)C, respectively. This clearly indicated that the D-values decreased with an increase in temperature but increased with an increase in the pH values. D-values during the conventional thermal heating varied from 102 to 24 s \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Temperature**} & \multicolumn{4}{c}{**D-Values (s)**} \\ \multicolumn{2}{c}{\({}^{\circ}\)**C**} & \multicolumn{4}{c}{**at pH 6.0**} & \multicolumn{4}{c}{**at pH 5.6**} & \multicolumn{4}{c}{**at pH 5.0**} \\ \hline  & Microwave & Thermal & Microwave & Thermal & Microwave & Thermal \\  & continuous flow & batch & continuous flow & batch & continuous flow & batch \\ \hline
65 & N/A & N/A & 27 & 198 & 16 & 102 \\ \hline
70 & 89 & 138 & 15 & 114 & 8 & 66 \\ \hline
75 & 61 & 120 & 12 & 66 & 5 & 24 \\ \hline
80 & 43 & 66 & 6 & 50 & N/A & N/A \\ \hline
85 & 22 & N/A & N/A & N/A & N/A & N/A \\ \hline z-value & & & & & & \\ \({}^{\circ}\)C & 25 & 33 & 23 & 30 & 20 & 21 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Thermal kinetics parameters (D-, z-values) comparison of TTI from BBA under conventional batch heating and MW continuous-flow heating conditions. Figure 8: Time-temperature profile of the continuous-flow microwave vs. the water-bath heating condition at exit temperature 70 \({}^{\circ}\)C. The black and pink lines demonstrate curve fitting. at pH 5.0 between 65 and 75 \({}^{\circ}\)C, from 198 to 50 s at pH 5.6 between 65 and 80 \({}^{\circ}\)C, and from 138 to 66 s at pH 6.0 between 70 and 80 \({}^{\circ}\)C. Comparing the common temperature ranges of 65-75 \({}^{\circ}\)C at pH 5.0-5.6 or 70-80 \({}^{\circ}\)C at pH 5.6-6.0, the D-values associated with microwave heating were much lower than those obtained for conventional batch heating. These are clearly illustrated in Figures 9 and 10 as D-value curves. Most importantly, the D-values obtained under conventional batch heating were four to eight times higher than those obtained under microwave heating at both pH 5.6 and 5.0. This indicates that the microwave continuous-flow heating condition is much more efficient at inactivating enzymes than the conventional thermal treatment. The temperature sensitivity indicator, z-value, ranged from 20 to 25 \({}^{\circ}\)C for microwave heating and 21 to 33 \({}^{\circ}\)C for thermal heating, again increasing with pH, but also demonstrating small differences. Earlier studies also reported the D-values associated with microwave heating to be considerably lower than the corresponding values found under both conventional batch  
Figure 10: Temperature sensitivity comparison between continuous-flow microwave heating and conventional batch heating at pH 5.0. Figure 9: Temperature sensitivity comparison between continuous-flow microwave heating and conventional batch heating at pH 5.6.  
and even continuous-flow thermal holding conditions [25]. [PERSON] et al. [26] attributed the differences found in the destruction kinetics between the conventional and microwave heating to different heating kinetics and to non-uniform local temperature distributions during microwave heating rather than the existence of non-thermal effects. [PERSON] and [PERSON] [27] evaluated the injury of _E. coli_ during pasteurization with microwaves in a tubular flow reactor, and they indicated that the destruction effect is the influence of the flow behavior and the other experimental conditions.