## 2 Results and Discussion
### Physicochemical Characterization of the Residual Babassu oil and Free Fatty Acids  
Table 3 shows the results of the physicochemical characterization of the residual babassu oil and the free fatty acids obtained after the chemical hydrolysis. The data obtained were compared with the values determined by Codex Alimentarius (International Food Standards) [56] and with results found in the literature for babassu oil and soybean oil, which is the most used raw material for biodiesel production in Brazil [57]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Fatty Acid** & **Nome** & **Formula** & **Molecular Weight (g/mol)** & **Percentage (\%)** \\ \hline C6:0 & Caproic Acid & C6H12O2 & 116.15 & 0.80 \\ C8:0 & Caprylic Acid & C8H16O2 & 144.21 & 9.64 \\ C10:0 & Capric Acid & C10H20O2 & 172.26 & 6.85 \\ C12:0 & Lauric Acid & C12H24O2 & 200.31 & 41.55 \\ C14:0 & Myristic Acid & C14H28O2 & 228.37 & 14.01 \\ C16:0 & Palmitic Acid & C16H32O2 & 256.40 & 6.96 \\ C18:0 & Stearic Acid & CH3(CH2)16 COOH & 284.48 & 2.66 \\ C18:1n9c & Oleic Acid & C18H34O2 & 282.47 & 11.04 \\ C18:2n6c & Linoleic Acid & C18H32O2 & 280.44 & 1.76 \\
**Others** & - & - & - & 4.73 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Percentages of free fatty acids in the chemical composition of residual oil from babassu. Figure 1: Chromatogram obtained by GC for the determination of the free fatty acids in the residual oil from babassu. Based on Table 3, the value of the acidity index obtained in the analyzes for the residual babassu oil showed a high value in comparison to the value determined by Codex Alimentarius and the values reported in the literature, which confirms that it is a residual oil. The acidity index deals with the conservation status of oils; due to factors such as exposure to light and heating, the breakdown of triglycerides is enhanced, causing the formation of free fatty acids accompanied by the formation of rancid [63]. Through the acidity index, it was possible to verify the efficient formation of free fatty acids from the saponification reaction followed by acid hydrolysis, since the acid value increased from 4.85 mgKOH/g to 174.44 mgKOH/g. As the present study deals with an esterification reaction using a lipase as biocatalyst, acidity is not a problem. According to [PERSON] et al. (2017) [21], in the case of a biodiesel production using enzymatic catalysts, the formation of soaps does not occur, which favors the increase in the reaction yield and avoids the necessity of washing step. The saponification index aims to establish the degree of deterioration of oils and fats; its main function is to verify adulterations by low quality oils, the lower the molecular weight of fatty acids, the higher their saponification rate [64]. In the studies carried out by ([PERSON] et al. 2019) [58], the authors determined the values for the saponification index of some oilseed plants most used in the production of biodiesel. In their studies, oil from canola showed a value of 111.61 mgKOH/g, oil from sunflower 129.54 mgKOH/g, oil from soybean of 109.17 mgKOH/g. In the present study, the saponification value showed a relatively high value of 271.94 mgKOH/g, which means that it contains more saturated fatty acids, thus allowing the saponification followed by acid hydrolysis to be successful. Oxidative stability is a property that depends on the proportions of saturated and unsaturated fatty acids present in the oils used in the biodiesel production; the high degree of unsaturation favors the oxidation and degradation of oilseeds [65]. Oxidative stability can be defined as the time required to reach the point where the degree of oxidation increases abruptly [66]. Oxidation of lipids is a degradative process, which can lead to loss of oil stability. This process can be favored and intensified by the action of light, which acts as a catalyst [67]. Babassu is rich in lauric acid, a saturated compound that does not favor oxidative rancidity.