Microbial biodiesel production: From sucrose-based carbon sources to alkyl esters via enzymatic transesterification

Sucrose, in contrast to glucose, is a lower-cost carbon source. This manuscript discloses that its use in submerged fungal growth promotes lipids more suitable to biodiesel production due to lower unsaturation indexes. The wild strain of Mucor circinelloides URM 4182, a potential source of microbial lipid, was grown on three sucrose-based carbon sources: commercial brown sugar, sugarcane juice, and sugarcane syrup, achieving biomass accumulation productivities up to 3.62 +/- 0.04 g L-1 day(-1), and lipid productivities as high as 0.93 +/- 0.01 g L-1 day(-1). Lipid extraction was performed using ethanol, a green alternative to petroleum-derived solvent, and characterized according to their fatty acid distribution, from which C16:0 and C18:1 stand as the most abundant fatty acids. Extracted lipids were converted to ethyl esters via lipase-catalyzed reactions achieving ester contents up to 97.4% and low contents of mono- and diacylglycerols (1.9% and 1.0%, respectively). The interest in utilizing sucrose-based sources is due to the wide abundance of such feedstock in sugarcane-producing regions, and due to the potential of increasing value to these low-cost carbon sources. The results presented herein demonstrate a simple, yet efficient, process of converting sucrose and its derivatives to microbial biodiesel using green-chemistry processes, such as lipid extraction using ethanol, avoiding the use of harsh and toxic chemicals commonly utilized, and enzyme-catalyzed reactions. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.