Effect of adsorption/desorption of substrates/products during isobutyl propionate synthesis over CalB Immo PlusTM in solid/gas biocatalysis

This work revisits the potential of Solid/Gas (S/G) biocatalysis for sustainable ester synthesis, focusing on isobutyl propionate (isoPro) production from propionic acid (aciP) and isobutyl alcohol (isoB) using CalB Immo Plus (TM) (CalB-IP), Candida antarctica lipase B (CalB) supported on ECR1030M (ECR). Our research, conducted in a bench-scale S/G bioreactor, describes the role of adsorption-desorption and intraparticle mass transfer on the production rate of isoPro. Three reaction scenarios were examined at 55 degrees C: simultaneous introduction of both substrates into the reactor; CalB-IP saturation with isoB followed by the supply of aciP; and vice versa, with aciP saturation preceding isoB. Adsorption-desorption-based experiments were conducted to determine breakthrough curves for isoB, aciP, and isoPro over ECR or CalB-IP at 55 degrees C. ECR exhibited significant adsorption capacity, with aciP>isoPro>isoB, in a reversible process. At pseudo-steady state, aciP and isoB were adsorbed at 86% and 84%, respectively, on ECR; while the remaining 14% and 16%, respectively, were adsorbed on the enzyme surface, involving irreversible binding. The experimentation also considered the influence of water activity (a(w): 0.11-0.75) on experimental responses. Production rates of isoB adsorption and isoPro were sensitive to a(w), while aciP adsorption remained insensitive to a(w). At a(w) = 0.75, isoB adsorbed 35% less over CalB-IP than at a(w) = 0.11. Additionally, at a(w) = 0.75, the production of isoPro at the bioreactor outlet in the pseudo-steady state was 33.5% less than when a(w) = 0.11. These findings offer valuable insights for designing S/G bioreactors, thereby advancing the industrial implementation of sustainable ester synthesis.