## 2 Results and Discussion
### Modification of the External and Internal Texture of Biocatalyst  
The Novozym(r) 435 is produced from immobilization of the lipase B from _Candida antarctica_, adsorbed on a macroporous resin composed by poly (methyl methacrylate acid) (PMMA), crosslinked with divinylbenzene (DVB). It is reported that after the esterification reaction may occur the enzyme desorption [93]. Thus, FTIR spectra were obtained for the biocatalyst before (Figure 5a) and after (Figure 5b) the esterification reaction of free fatty acids, in order to obtain information about its structure. For the Novozym(r) 435 samples, broadbands in the range of 3600-3100 cm\({}^{-1}\) correspond to O-H and N-H stretching. The vibrational modes of asymmetric and symmetric stretching methyl groups were observed at 2950 and 2875 cm\({}^{-1}\), respectively. The band centered in 1732 cm\({}^{-1}\) can be related to the stretching vibration of carbonyl groups v(C=O) of the PMMA [94]. The bands at 1452 and 1512 cm\({}^{-1}\) confirm the presence of DVB in the structure of the biocatalyst since it can be associated with the bond stretching between carbon atoms in the aromatic ring [95]. Moreover, the bands observed from 869 to 682 cm\({}^{-1}\) are characteristic of the C-H out-of-plane bending of alkyl-substituted benzene. The presence of the lipase B from _Candida antarctica_ can be confirmed by bands at 1654 and 1539 cm\({}^{-1}\) that correspond to the Amide I and Amide II [96]. These same bands also were observed in the spectrum obtained after the esterification reaction. However, it is important to analyze not only the profile and the association of the bands. The ratio between the bands at 1732 cm\({}^{-1}\) and 1654 cm\({}^{-1}\) can be used to verify if there is any charge in the biocatalyst related to the enzyme or support. For the Novozym(r) 435 (Figure 5a), this ratio (3.663) is greater than catalyst after reaction (Figure 5b) (2.678), suggesting a small change in the support/enzyme ratio after the reaction. Figure 4: Cycles of activity of Novozym® 435 in the enzymatic esterification of babassu free fatty acids at 48 °C, molar ratio 1:18 (FFAs/alcohol), biocatalyst content 0.14 g and 4 h of reaction. Figure 5: Fourier Transform Infrared (FTIR) spectrum of the Novozym® 435 before (**a**) and after (**b**) the esterification reaction. SEM images were used to evaluate the morphology and textural properties of the biocatalyst before (Figure 6a,b) and after (Figure 6c,d) the esterification reaction. The biocatalyst showed a spherical morphology with a diameter ranging from 600 to 700 \(\upmu\)m. Additionally, it was observed for both samples a low roughness on their surface. In order to evaluate the dispersion of elements in the surface of the material, Energy Dispersive X-ray Spectroscopy EDS images were also obtained (inset Figure 6b,d). The dispersion of elements in the samples is very similar (Table 7), not being observed any significant change in the surface of the biocatalyst after the esterification reaction. FTIR is one of the most powerful techniques of molecular analyses for material characterization. This technique has high-sensibility and allows the identification of many functional groups. Thus, since Novozym(r) 435 is formed by immobilization of the lipase B from _Candida antarctica_ adsorbed on a macroporous resin composed by poly(methyl methacrylate acid) (PMMA) crosslinked with divinylbenzene (DVB), it is possible to use the FTIR as a tool to the identification of subtle change in this materials. Besides, this technique is based on the analyses of a certain amount of materials, usually in the milligram range. SEM and elementary analysis from EDS spectrum are usually obtained from the upper few micrometers of the sample, i.e., it is not a bulk analysis technique. However, these techniques provide information on a small area of the sample, since the measurement is being carried on the surface of a single particle or in a small set of particles.