Comparison of SHF and SSF processes from steam‐exploded wheat straw for ethanol production by xylose‐fermenting and robust glucose‐fermenting Saccharomyces cerevisiae strains

Abstract

In this study, bioethanol production from steam-exploded wheat straw using different process configurations was evaluated using two Saccharomyces cerevisiae strains, F12 and Red Star. The strain F12 has been engineerically modified to allow xylose consumption as cereal straw contain considerable amounts of pentoses. Red Star is a robust hexose-fermenting strain used for industrial fuel ethanol fermentations and it was used for comparative purposes. The highest ethanol concentration, 23.7 g/L, was reached using the whole slurry (10%, w/v) and the recombinant strain (F12) in an SSF process, it showed an ethanol yield on consumed sugars of 0.43 g/g and a volumetric ethanol productivity of 0.7 g/L h for the first 3 h. Ethanol concentrations obtained in SSF processes were in all cases higher than those from SHF at the same conditions. Furthermore, using the whole slurry, final ethanol concentration was improved in all tests due to the increase of potential fermentable sugars in the fermentation broth. Inhibitory compounds present in the pretreated wheat straw caused a significantly negative effect on the fermentation rate. However, it was found that the inhibitors furfural and HMF were completely metabolized by the yeast during SSF by metabolic redox reactions. An often encountered problem during xylose fermentation is considerable xylitol production that occurs due to metabolic redox imbalance. However, in our work this redox imbalance was counteracted by the detoxification reactions and no xylitol was produced.

Sequential Targeting of Xylose and Glucose Conversion in Fed-Batch Simultaneous Saccharification and Co-fermentation of Steam-Pretreated Wheat Straw for Improved Xylose Conversion to Ethanol

“…The SHCF strategy elicited overall ethanol yields of 83 and 75% of the theoretical maximum, respectively, for co-fermentation of mild and severe slurry, whereas the SSCF strategy resulted in overall ethanol yields of 92 and 84%, respectively (Table 3). The improvement in ethanol yields reinforced the notion that SSF typically results in higher yields than SHF [25,26].…”

“…The continuous release of glucose by enzymatic hydrolysis helps maintain low glucose concentrations, which kinetically favor xylose utilization in recombinant S. cerevisiae strains [21]. Typically, ethanol productivity [24] and yield are higher in SSCF than with separate hydrolysis and co-fermentation [25,26]. Ethanol yields in SSCF have been improved with modifications to the co-fermentation strategy, such as fed-batch strategies [27], enzyme feeding [28], and prefermentation [29] and combinations thereof [30][31][32].…”

Enzymatic Conversion of Sugar Beet Pulp: A Comparison of Simultaneous Saccharification and Fermentation and Separate Hydrolysis and Fermentation for Lactic Acid Production

“…However, a comparison of SHF and SSF conducted by Rana et al (40) found that SSF was more efficient than SHF, despite using a lower reaction temperature, which is suboptimal for enzyme hydrolysis. The lower temperatures and shorter operating times required for SSF processes result in energy savings, which are a significant advantage of the system (16,41). However, some disadvantages may occur during scaling-up.…”

comparação entre processos em SHF e em SSF de bagaço de cana-de-açúcar para a produção de etanol por Saccharomyces cerevisiae

“…6 Após o pré-tratamento do material lignocelulósico, as próximas etapas para a obtenção de etanol são a hidrólise enzimática e a fermentação que podem ocorrer em separado ou simultaneamente. 7 A vantagem do processo em separado (SHF) é que as temperaturas da hidrólise enzimá-tica e da fermentação podem ser otimizadas. 8 A hidrólise enzimática é realizada por celulases (endoglucanase e exoglucanase), que quebram a celulose em celobiose, e esta é, subsequentemente, convertida em duas moléculas de glicose pela β-glucosidase.…”