Development of a green integrated process for biodiesel esters production: Use of fermented macaúba cake as biocatalyst for macaúba acid oil transesterification

In this study, a new green integrated process for biodiesel ester production was developed, consisting of the enzymatic transesterification of acid oil from macaúba palm tree (Acrocomia aculeata) catalyzed by dry fermented solid (DFS) with lipase activity, which was obtained from solid-state fermentation (SSF) of macaúba cake. Analysis of statistical experimental designs showed that nitrogen supplementation of macaúba cake improved production of lipases displaying esterification capacity by Rhizomucor miehei. The conditions chosen to produce R. miehei DFS were cake supplementation with 2 wt% urea, 60 wt% of initial moisture during 48 h of fermentation at 40°C. DFS showed, by zymography assays, at least one enzyme that was different from those that are present in the commercial lipase of R. miehei. Furthermore, DFS was used in transesterification reactions between macaúba acid oil and alcohol (methanol or ethanol), and the ester content obtained was 92%. This is the first time that this integrated process using low-cost biocatalysts and a low-value oil derived from the processing of the same fruit was used for biodiesel ester production, reducing costs and logistic constraints, and optimizing the raw material utilization.     

Study of oxygen reduction on copper applied to the peroxidase-mediated oxidation of methylene blue

The kinetics of oxygen reduction was studied on copper in tartarate solutions using a rotating disc electrode. The effect of pH on the cathodic reduction was examined. AC impedance and cathodic polarization curves showed that the reaction is partially controlled by mass transport. At high current densities, the limiting current values showed that O₂ is reduced mainly through the four electron pathway. From measurements of density and viscosity and data taken from Levich and Tafel plots, diffusion coefficients for oxygen in tartarate medium were calculated. Peroxidase-mediated oxidation of methylene blue (MB) results using electrogenerated H₂O₂ on copper electrode showed that O₂ reduction reaction occurs in two steps producing the adsorbed intermediate species H₂O₂ by k ₂. In the absence of peroxidase, the hydrogen peroxide elimination has to be rapid with k ₃ ≫ k _M. The MB oxidation by lignin peroxidase using electrogenerated H₂O₂ was studied. After 24 h LiP is able to oxide the MB, producing different oxidized forms: azure C and thionine, with yield of 23% and 66%, respectively.