Overcoming inhibitors in a hemicellulosic hydrolysate: improving fermentability by feedstock detoxification and adaptation of Pichia stipitis

Abstract

In order to improve the fermentative efficiency of sugar maple hemicellulosic hydrolysates for fuel ethanol production, various methods to mitigate the effects of inhibitory compounds were employed. These methods included detoxification treatments utilizing activated charcoal, anion exchange resin, overliming, and ethyl acetate extraction. Results demonstrated the greatest fermentative improvement of 50% wood hydrolysate (v/v) by Pichia stipitis with activated charcoal treatment. Another method employed to reduce inhibition was an adaptation procedure to produce P. stipitis stains more tolerant of inhibitory compounds. This adaptation resulted in yeast variants capable of improved fermentation of 75% untreated wood hydrolysate (v/v), one of which produced 9.8 g/l ± 0.6 ethanol, whereas the parent strain produced 0.0 g/l ± 0.0 within the first 24 h. Adapted strains RS01, RS02, and RS03 were analyzed for glucose and xylose utilization and results demonstrated increased glucose and decreased xylose utilization rates in comparison to the wild type. These changes in carbohydrate utilization may be indicative of detoxification or tolerance activities related to proteins involved in glucose and xylose metabolism.

Dissecting a complex chemical stress: chemogenomic profiling of plant hydrolysates

“…These inhibitors have a significant impact on growth and fermentation of bacteria and yeast, thus preventing efficient biofuel production. There are three common approaches to deal with fermentation inhibitors: prevent their formation by reducing the severity of pretreatment, remove inhibitors by detoxification, or improve the tolerance of the host organism (Palmqvist and Hahn‐Hägerdal, 2000a; Nilvebrant et al , 2001; Martín et al , 2007a; Parawira and Tekere, 2011; Stoutenburg et al , 2011). All three methods can be successful and are expected to have a significant economic impact (Klein‐Marcuschamer et al , 2010; Tao et al , 2011), but here we will focus on improving tolerance.…”

Comparison of digestibility of wood pulps produced by the sulfate and TMP methods and woodchips of various botanical origins and sizes

“…Furthermore, the harsh thermal pretreatment leads to losses in sugars and generates fermentation inhibitors like furfural, 5-hydroxymethylfurfural (5HMF), and phenolic acids (Stoutenburg et al 2011). These harmful compounds, reducing productivity of fermentation processes, need to be removed from biomass hydrolysates that increases overall costs of lignocellulose conversions.…”

“…In contrast to cellulose, which is characterized by a highly regular structure, irrespective of its source, the structure of hemicelluloses, which are polymers of pentoses and hexoses, depends on their botanical origin. Xylose and other pentoses, derived from hemicelluloses, are usually less efficiently converted to fermentation products than glucose (Stoutenburg et al 2011). Their content in enzymatic hydrolysates depends on conditions of biomass pretreatment.…”

Enhanced ethanol production from sugarcane bagasse hydrolysate with high content of inhibitors by an adapted barnettozyma californica

“…The effect of various concentrations of hydrolysate (SBH and CSBH) on the growth of adapted and wild type yeast strains was investigated. The tolerance of the fermenting organism to hydrolysate inhibitors is particularly important, so different wild type and adapted yeasts such as P. stipitis , Saccharomyces cerevisiae , and Candida shehatae have been investigated for their fermentation performance in the similar literatures .…”

“…and resuspended in fresh hydrolysate. This process was upgraded to higher hydrolysate concentrations until the adapted culture was continuously subcultured in 100% CSBH for more than 10 batches .…”