Inactivating effects of lignin-derived compounds released during lignocellulosic biomass pretreatment on the endo-glucanase catalyzed hydrolysis of carboxymethylcellulose: A study in continuous stirred ultrafiltration-membrane reactor

This study focusses on the reversible/irreversible damage that selected phenolic compounds, released during steam-explosion pretreatment, mandatory for cellulose accessibility, causes on both stability and activity of a commercial cellulase (half-life = 173 h) during carboxymethyl-cellulose hydrolysis. Long-term experiments performed in continuous stirred UF-membrane bioreactors, operating at steady-state regime, in controlled operational conditions, allowed evaluating the inactivation-constant in the phenol presence (kd1) and after its removal (kd2) from the reactor feed. p-Hydroxybenzoic acid (1 and 2 g L−1) are the extreme limits in the inactivating effect with enzyme half-lives 99.02 and 14.15 h, respectively. The inactivation reversibility was assessed for vanillic acid, p-hydroxybenzoic acid, syringaldehyde, p-coumaric acid, being kd1 > kd2. p-Hydroxybenzaldehyde and protocatechuic acid irreversibly affected cellulase stability increasing its inactivation with kd2 > kd1. p-Hydroxybenzaldehyde, 1 g L−1, syringaldehyde, and vanillin, at 2 g L−1, had similar kd1 ÷ kd2.