From batch to fed-batch and to continuous packed-bed reactors: Lipase-catalyzed esterifications in low viscous deep-eutectic-solvents with buffer as cosolvent

•Low viscous DES-water blends can be used in continuous processes for biocatalysis.•The pH control increases the conversion, using DES in a fed-batch reactor.•Fed-batch reactor reached the highest concentration of product 33 g/L.•The semicontinuous and continuous bioreactors reached similar productivities.•Biocatalyst stability was high in a packed-bed reactor, without loss for 10 days. This work explores for the first time the use of Deep Eutectic Solvents (DES) with phosphate buffer 100 mM pH 7 as cosolvent (10% v/v) in biocatalytic reactions in fed-batch and packed-bed bioreactors. The lipase-catalyzed esterification of glycerol and benzoic acid is studied, as it involves two substrates with different polarities (for which DES are needed). In the fed-batch bioreactor, the highest conversion (90%) was obtained at a substrate flow rate of 0.01 mL/min. The fed-batch operation increased the conversion by 59% compared to the batch mode. Regarding productivity, semi-continuous and continuous bioreactors showed analogous results. Upon recirculation of the reaction media in the continuous bioreactor, a conversion of 67% was achieved in 7 cycles of operation. The stability of the biocatalyst in the packed-bed bioreactor decreased only 2% in 10 days, demonstrating the attractiveness that low viscous DES-water mixtures with continuous processes may have.