Influence of Lignocellulose-Derived Aromatic Compounds on Oxygen-Limited Growth and Ethanolic Fermentation by Saccharomyces cerevisiae

Abstract

Phenolic compounds released and generated during hydrolysis inhibit fermentation of lignocellulose hydrolysates to ethanol by Saccharomyces cerevisiae. A wide variety of aromatic compounds form from lignin, which is partially degraded during acid hydrolysis of the lignocellulosic raw material. Aromatic compounds may also form as a result of sugar degradation and are present in wood as extractives. The influence of hydroxy-methoxy-benzaldehydes, diphenols/quinones, and phenylpropane derivatives on S. cerevisiae cell growth and ethanol formation was assayed using a defined medium and oxygen-limited conditions. The inhibition effected by the hydroxy-methoxy-benzaldehydes was highly dependent on the positions of the substituents. A major difference in inhibition by the oxidized and reduced form of a diphenol/quinone was observed, the oxidized form being the more inhibitory. The phenylpropane derivatives were examined with respect to difference in toxicity depending on the oxidation-reduction state of the gamma-carbon, the presence and position of unsaturated bonds in the aliphatic side chain, and the number and identity of hydroxyl and methoxyl substituents. Transformations of aromatic compounds occurring during the fermentation included aldehyde reduction, quinone reduction, and double bond saturation. Aromatic alcohols were detected as products of reductions of the corresponding aldehydes, namely hydroxy-methoxy-benzaldehydes and coniferyl aldehyde. High molecular mass compounds and the corresponding diphenol were detected as products of quinone reduction. Together with coniferyl alcohol, dihydroconiferyl alcohol was identified as a major transformation product of coniferyl aldehyde.

Progress in Metabolic Engineering of Saccharomyces cerevisiae

“…However, this portion can be burned for efficient heating and electrical production and, in the longer term, specialty chemical production (92). The negative impacts of lignin on lignocellulose-based fermentative processes are (i) inhibition of cellulases (50) and (ii) formation during lignocellulose pretreatment of phenolic degradation products which inhibit microbial growth (11,192).…”

Bioethanol a Microbial Biofuel Metabolite; New Insights of Yeasts Metabolic Engineering

“…After this step, the lignocellulose materials become dissolvable in the liquid media that consists of formic, acetic and levulinic acids, as well as phenolic and furans compounds that formed during pretreatment step [215]. Since all of the released chemical compounds had a negative impact on the growth of yeast, bioethanol production and fermentation processes at all [216], alot of endeavors have been exerted to obviate the production of these harmful chemical compounds [4]. An alternative way for overcoming this obstacle is to minimize their concentrations by different application method of detoxification [215], but more procedures have a negative influence on the balance of energy and increase the cost of product which makes it unavailable for application in all conditions [3].…”

Latest Frontiers in the Biotechnologies for Ethanol Production from Lignocellulosic Biomass

“…Some researches indicated that these compounds partition into cells membranes cause loss of integrity (Palmqvist & Hann-Hägerdal, 2000). It was established that low molecular weight phenolic compounds are more inhibitory than those with high molecular weight (Klinke et al, 2004) and furthermore, the substituent position influenced the compounds toxicity (Larsson et al, 2000). Among the phenolic compounds, vanillin was shown to be a strong inhibitor of growth and ethanol production in P.stipitis, C. shehatae and S.cerevisiae at the concentration of 1 g/L (Delgenes et al, 1996).…”