Main and interaction effects of acetic acid, furfural, and p‐hydroxybenzoic acid on growth and ethanol productivity of yeasts

Abstract

The influence of the factors acetic acid, furfural, and p-hydroxybenzoic acid on the ethanol yield (Y EtOH) of Saccharomyces cerevisiae, bakers' yeast, S. cerevisiae ATCC 96581, and Candida shehatae NJ 23 was investigated using a 2 3-full factorial design with 3 centrepoints. The results indicated that acetic acid inhibited the fermentation by C. shehatae NJ 23 markedly more than by bakers' yeast, whereas no significant difference in tolerance towards the compounds was detected between the S. cerevisiae strains. Furfural (2 g L −1) and the lignin derived compound p-hydroxybenzoic acid (2 g L −1) did not affect any of the yeasts at the cell mass concentration used. The results indicated that the linear model was not adequate to describe the experimental data (the p-values of curvatures were 0.048 for NJ 23 and 0.091 for bakers' yeast). Based on the results from the 2 3-full factorial experiment , an extended experiment was designed based on a central composite design to investigate the influence of the factors on the specific growth rate (µ), bio-mass yield (Y x), volumetric ethanol productivity (Q EtOH), and Y EtOH. Bakers' yeast was chosen in the extended experiment due to its better tolerance towards acetic acid, which makes it a more interesting organism for use in industrial fermentations of lignocellulosic hydrolysates. The inoculum size was reduced in the extended experiment to reduce any increase in inhibitor tolerance that might be due to a large cell inoculum. By dividing the experiment in blocks containing fermentations performed with the same inoculum preparation on the same day, much of the anticipated systematic variation between the experiments was separated from the experimental error. The results of the fitted model can be sum-marised as follows: µ was decreased by furfural (0-3 g L − 1). Furfural and acetic acid (0-10 g L − 1) also interacted negatively on µ. Furfural concentrations up to 2 g L −1 stimulated Y x in the absence of acetic acid whereas higher concentrations decreased Y x. The two compounds interacted negatively on Y x and Y EtOH. Acetic acid concentrations up to 9 g L −1 stimulated Q EtOH , whereas furfural (0-3 g L −1) decreased Q EtOH. Acetic acid in concentrations up to 10 g L −1 stimulated Y EtOH in the absence of furfural, and furfural (0-2 g L −1) slightly increased Y EtOH in the absence of acetic acid whereas higher concentrations caused inhibition. Acetic acid and furfural interacted negatively on Y EtOH .

Ethanol Production from Hydrothermally-Treated Biomass from West Africa

“…Degradation of wheat straw into organic acids was also low, but was higher than the total organic acids content (<0.23% w/w) obtained by AmbyeJensen et al (2013) for the HTT of wheat straw at severities of 3.06 to 3.65. According to Palmqvist et al (1999), inhibition of yeast by carboxylic acids is significant if the concentration is above 10 g/L. The total carboxylic acids concentration remained below that critical level in this study.…”

Liquefaction of lignocellulose at high‐solids concentrations

“…Another problem associated with application of higher solids concentrations is the increasing concentration of inhibitors like acetic acid, furfural, 5-hydroxymethyl furfural, and phenolic lignin degradation products, which are commonly formed during especially acid catalyzed pretreatment. High-inhibitor concentrations might severely hamper the performance of the fermenting microorganism and in worst-case result in a non-fermentable hydrolyzate Palmqvist et al, 1999).…”

Influence of solid loading on D-xylose production through dilute sulphuric acid hydrolysis of olive stones

“…When the target is the recovery of D-xylose instead of D-glucose, dilute acid hydrolysis is still a preferential process over enzymatic hydrolysis due to its lower cost and faster kinetics (García Martín et al, 2013). However, the major drawbacks of acid hydrolysis are potential sugar degradation towards furfural and 5-hydroxymethyl-furfural along with acetic acid generation, which can provoke yeast inhibition in the subsequent fermentation for ethanol or xylitol production (Palmqvist et al, 1999;Montané et al, 2002;García et al, 2012). Sulphuric acid is usually used instead of other acids, such as hydrochloric, nitric and phosphoric acid, because of its low volatility, lower corrosion on equipment and reduced cost (García Martín et al, 2013;Kim et al, 2014).…”