Furfural fermentation inhibition

The same conditions also resulted in the maximum glucose yield, 17.2 g/ 100 g of SFF. At the pretreatment conditions used, the formation of fermentation-inhibiting compounds was very low (results not shown) (16). The concentration of furfural in the slurry pretreated at 190°C for 10 min was about 0.3 g/L. No HMF was detected. 

The fermentation inhibitors include furan aldehydes, aliphatic acids, and phenolic compounds. The furan aldehydes, furfural, and hydroxymethyl furfural (HMF), are formed from pentoses and hexoses, respectively (4,5). Several studies indicate that furfural inhibits Saccharomyces cerevisiae, at least when present in high concentrations (6-10). HMF has a similar effect (11,12). 

Wood is about 65—75% carbohydrate and has been considered as a potential source of ethanol for fuel. The carbohydrate material can be hydrolyzed to monomer sugars, which in turn can be fermented to produce ethanol. However, wood carbohydrates are expensive to hydrolyze. Hydrolysis with acids and enzymes is impeded by the crystalline structure of cellulose. Lignin interferes with processing, and hydrolytic by-products such as furfural, acetic acid, and derivatives of lignin and extractives can inhibit fermentation. Research is still being conducted on wood hydrolysis to develop a process that is economically sound. Furfural is a useful chemical feedstock and results from the dehydration of pentose sugars. It can be obtained in 9 to 10% yield from the dilute acid hydrolysis of hardwoods (75). 

D. hansenii at concentrations above 0.5 g/1, and the inhibitory effects on fermentation increased with vanillin concentration up to 3 g/1. Furfural was less inhibitory to batch fermentations, with concentrations between 1 and 5 g/1 exhibiting similar effects [23], From experiments with brewers spent grain hydrolysate (85 g/1 xylose) pretreated in various manners (raw, treated with activated carhon, concentrated, or amended with xylose), it appears that total phenolics (3.93 g/1), including vanillin and syringaldebyde, are the most inhibitory compounds to C guilliermondii fermentations. The presence of furfural (0.61 g/1) did not effect the fermentation. Sanchez and Bautista [31] found that 2 g/1 fiirfiiral inhibits oxidative metabolism and fermentation by C. guilliermondii, and it has been previously observed that furfural concentrations below 1 g/1 are not inhibitory [32-33]. Keating et al. 

The main drawback of the acid hydrolysis processes is the formation of undesirable by-products. This not only lowers the yield of sugars, but several of the by-products severely inhibit the formation of ethanol in the fermentation process. Potential inhibitors are furfural, 5-hydro ethylfiirfural (HMF), levulinic acid, acetic acid, formic acid, uronic acid, 4-hydroxybenzoic acid, vanillic acid, vanillin, phenol, cinnamaldehyde, formaldehyde, etc. (I, 36). Some inhibitors, such as terpene compounds, are initially present in the wood, but apparently most of the inhibitors are formed in the hydrolysis process. 

Once the SE, LHW, AFEX, and DA pretreatment methods were selected, 24 possible combinations with the six conversion configurations are established. However, based on the pretreatment characteristics, only 16 potential combinations were considered (Eigure 2.12). SE pretreatment is not recommended for implementation with any configuration using solid-liquid separation because of the potential bioethanol inhibition due to high furfural and acetic acid compositions in the fermentation step. The AFEX pretreatment can be combined with separated enzymatic hydrolysis and cofermentation (SHCF) and... 

Bioethanol is produced from the hydrolysate of lignocellulosic substrate after pretreatment and enzymatic hydrolysis. With high conversion of carbohydrates, hexose and pentose can be fermented by commercial or engineered Saccharomyces cerevisiae or other microorganisms. Depending on the feedstock and pretreatment processes, various types of growth-inhibiting compounds have been discovered to hinder the performance of fermentation. For example, HMF and furfural formed from dehydration of... 

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