Lipase-catalyzed Production of Sugar Esters in Pressurized Fluid Media: A Review

Sugar esters (SE) are amphiphilic compounds containing hydrophilic moieties linked to hydrophobic parent structures with environmental-friendly features regarding non-toxicity, odorless, tasteless, and biodegradability as well as functional, emulsifying, stabilizing, dispersant, and detergent functions. The use of lipases as alternative biocatalysts to the alkaline compounds used industrially to produce SEs introduces interesting points to the process regarding energy consumption reduction, high selectivity, purer products production, and minimization of fossil-based solvents utilization. However, the usual organic solvents required in the reaction are harmful to enzymes, affecting their catalytic capacity. Accordingly, supercritical fluids (SCFs) are interesting options for the enzymatic process, especially carbon dioxide, which reaches such conditions under non-severe circumstances. SCFs have characteristics that make them attractive solvents for SEs production, allowing the manipulation of their properties to increase substrate solubility and reduce mass transfer limitations, intensifying process productivity. However, issues concerning with the strict operating conditions required by lipases and costs linked to project and equipments are shortcomings that must be considered. Therefore, this review gathers the main guidelines and opportunities that drive SEs production through enzymatic catalysis under supercritical conditions, as well as the challenges faced by this technology. Furthermore, technical aspects of properties and characteristics that justify the application of these compounds as well as considerations about how the main process parameters should be managed to enhance the substrates' conversion are also discussed. Future perspectives indicate that the design of cost-effective bioreactors to improve performance as well as protein engineering to enhance lipases' stability are points to be explored.