Use of Rhizomucor miehei fermented babassu cake (an agro-product residue) as efficient biocatalyst for macaúba acid oil deacidification in solvent-free medium: Transforming a non-edible crop product in a favourable biodiesel feedstock

Macaúba, a native South American palm, is used to recover degraded areas in important Brazilian biomes and presents a high oil productivity. Macaúba pulp oil is a sustainable alternative for biodiesel production. However, its high acidity represents a problem for its use. This paper shows an enzymatic process to reduce the acidity of macaúba pulp oil (9.5 wt% acidity) using a low-cost agro-industrial by-product to get a solid-state fermented solid with lipase activity from Rhizomucor miehei. Ethanol, methanol and glycerol were evaluated as acyl acceptors for the esterification of the free fatty acids (FFA) in the oil. Methanol was the best acyl acceptor, with 3.6 and 2.4 times higher deacidification rate than ethanol and glycerol, respectively, for reactions conducted with FFA to alcohol stoichiometric molar ratio. The alcohol stepwise addition strategy gave better results for all tested acyl acceptors. At the best reaction condition (methanol/FFA molar ratio of 6:1, methanol stepwise addition), the desired FFA esterification (acidity of 0.4 wt%, compatible with biodiesel plants requirements) was attained after only 2.5 h. This means the conversion of two no interesting crop products into valuable products.