3.4. Kinects of Ultrasound-assisted Enzymatic Hydrolysis with Oil-Free Seeds
In the optimal experimental conditions obtained through Equation (4) (68% power, 1.7 B/O, and 0.06 C/S), a kinetic experiment was performed, and the result is shown in Figure 6 . As observed, after 5 minutes, the reaction reaches equilibrium with approximately 75% FFA (0.79 mol kg-1).
Since there was no further advance of the hydrolysis reaction after 5 minutes and to evaluate the deactivation of the enzymatic catalyst, one following step was carried out for extra 30 minutes in a refrigerated incubator (140 rpm). A yield of 76.6 ± 2.62% was achieved, indicating the catalyst deactivation, and therefore, the hydrolysis reaction could not proceed.
To evaluate the effectiveness of the ultrasound, an experiment was conducted under the optimal conditions found with Equation 5 in a refrigerated incubator (140 rpm) for 3 minutes and the yield obtained was 8.97 ± 2.62%, considering that the yield after 3 minutes of reaction under ultrasound effect was 71.47± 2.62%, it is clear that the use of ultrasound represents an excellent improvement for the hydrolysis reaction.
MAG, DAG, and TAG (in mol kg-1) concentration profiles are displayed in Figure 6. The expected behaviors for the concentration profiles of TAG (Figure 6 (d)), DAG (Figure 6 (c)), and MAG (Figure 6 (b)) can be observed for this case as in the previous case, decrease in TAG concentration and FFA concentration increase (Figure 6 (a) and parabolic behaviors for DAG and MAG concentrations. The model values for the concentration profiles of glycerol (Figure 6 (e)) and water (Figure 6 (f)) are also shown in Figure 6. The equilibrium of the enzymatic hydrolysis reaction was reached in 5 min, achieving 75% (≈ 0.79 mol kg), a lower value when compared to in natura seeds as the catalyst. In Table 5 are presented the values for the estimated parameters from the fitting of the model with the experimental kinetic data, and the curves are displayed in Figure 6. The coefficient of determination values (R²) were 0.99, 0.97, 0.99, and 0.99 for TAG, DAG, MAG, and FFA experimental data, respectively. All results imply a satisfactory description of the experimental data by the kinetic model.