## 1 Introduction
In this set of experiments, a combination of _sn_-1,3 specific lipase (ET2.0) and a _sn_-2 specific lipase (CALA) was also evaluated. These reactions were conducted in the absence of emulsifier or buffer agents, which require vigorous mechanical stirring to prepare stable water/oil interfaces to improve the catalytic performance of lipases [30]. MAE production from the enzymatic esterification of FFA and fused oil, the latter being a valuable byproduct from bioethanol production comprising a mixture of ethanol, propanol, isobutanol, and isoamyl alcohol (the main component) [31; 32], was performed in an eco-friendly and sustainable process (solvent-free system) [33]. The production of industrial esters via a two-step process (hydrolysis + esterification or \"hydroesterification\") has been demonstrated to be advantageous, since direct enzymatic transesterification of triacylglycerleys requires either long reaction times or high temperatures to obtain high yields [34; 35]. Since esterification is a reversible reaction [36; 37; 38; 39], water removal strategies were evaluated by performing the reaction in closed or open reactors in the absence or in the presence of molecular sieves to increase ester production. Moreover, previous studies have also demonstratedthat using hydrophobic supports may prevent the formation of an aqueous phase in the biocatalysts' microenvironment that would drastically reduce their catalytic performance and reusability [39; 40]. For this purpose, ET2.0, a low-cost commercial lipase preparation with high catalytic activity in non-aqueous media [27; 41], was immobilized via physical adsorption on hydrophobic poly(styrene-divinylbenzene) (PSty-DVB) beads, and used as a heterogeneous biocatalyst. This low-cost heterogeneous biocatalyst has also demonstrated high catalytic performance and operational stability (reusability) for producing valuable esters using synthetic or natural starting materials [42; 43; 44]. The catalytic performance of this heterogeneous biocatalyst (immobilized lipase) was compared with its soluble form (crude lipase extract). Reusability tests of the biocatalyst after eight successive esterification batch reactions were also conducted in the absence (closed reactor) and presence (open reactor) of water removal strategies. The epoxidation of the produced MAE was performed via Prilezhaev epoxidation (or Prileschajew epoxidation) [11]. This reaction proceeds via the in situ generation of peracids (or peroxyacids) from reactions between carboxylic acids (commonly, formic and acetic acids) and hydrogen peroxide in an aqueous phase, followed by diffusion of peracid molecules to the oil phase to react with the double bonds [11; 16; 45]. In this study, formic acid, a valuable carboxylic acid from biomass-derived carbohydrates [46], was chosen as a homogeneous catalyst, given its high reactivity relative to acetic acid [15; 47; 48]. The different products were identified by \({}^{1}\)H NMR analysis, and their chemical properties were determined by standard methods. To the best of our knowledge, this is the first study that has investigated the production, via a three-step process, of EMAE from USCO and fused oil, two renewable and low-cost starting materials commonly found in several countries.