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.