Detoxification of furanic and phenolic lignocellulose derived inhibitors of yeast using laccase immobilized on bacterial cellulosic nanofibers

Abstract

Biotransformation of lignocellulose by microbial fermentation is usually preceded by thermo-chemical pretreatments followed by enzymatic hydrolysis of cellulose. Derivatives formed during the pretreatment of the lignocellulosic biomass inhibit enzymatic hydrolysis as well as microbial fermentation. Pretreated lignocellulose hydrolysate contains many derivatives of either furanic or phenolic inhibitory derivatives. In the present study, laccase was used to detoxify three different types of lignocellulosic derivatives that are highly toxic to microbial fermentation due to their low hydrophilic nature, namely furfural, acetosyringone, and coniferyl aldehyde. A minimal inhibitory concentration (MIC) test was carried out with Saccharomyces cerevisiae. The MIC of furfural, acetosyringone, and coniferyl aldehyde was 12 mM, 24 mM, and 1.5 mM, respectively. Laccase was immobilized on to cellulose nanofiber produced by Gluconacetobacter xylinus. Immobilized laccase showed a better pH and thermal stability than free laccase. Reuse of immobilized laccase retains 85% of its enzyme activity after 16 recycles. Immobilized laccase completely degraded the three lignocellulose inhibitory derivatives after 36 h of incubation at 40 °C. Finally, the degradation was confirmed by ultraviolet visible spectroscopy (UV–VIS spectrum), high performance liquid chromatography and liquid chromatography mass spectrometry. Interestingly, it was found that the effect of enzymatic degradation depends on the structural variation of the lignocellulosic derivatives as laccase alone detoxified the furfural and coniferyl aldehyde, whereas a redox mediator HOBt was needed for the detoxification of ketone based lignin derivative acetosyringone.