Reducing agents improve enzymatic hydrolysis of cellulosic substrates in the presence of pretreatment liquid

Enzymatic hydrolysis of pretreated lignocellulosic substrates has emerged as an interesting option to produce sugars that can be converted to liquid biofuels and other commodities using microbial biocatalysts. Lignocellulosic substrates are pretreated to make them more accessible to cellulolytic enzymes, but the pretreatment liquid partially inhibits subsequent enzymatic hydrolysis. The presence of pretreatment liquid from Norway spruce resulted in a 63% decrease in the enzymatic saccharification of Avicel compared to when the reaction was performed in a buffered aqueous solution. The addition of 15 mM of a reducing agent (hydrogen sulfite, dithionite, or dithiothreitol) to reaction mixtures with the pretreatment liquid resulted in up to 54% improvement of the saccharification efficiency. When the reducing agents were added to reaction mixtures without pretreatment liquid, there was a 13-39% decrease in saccharification efficiency. In the presence of pretreatment liquid, the addition of 15 mM dithionite to Avicel, α-cellulose or filter cake of pretreated spruce wood resulted in improvements between 25 and 33%. Positive effects (6-17%) of reducing agents were also observed in experiments with carboxymethyl cellulose and 2-hydroxyethyl cellulose. The approach to add reducing agents appears useful for facilitating the utilization of enzymes to convert cellulosic substrates in industrial processes.     

Effect of pretreatment with organic solvent on enzymatic digestibility of cauliflower wastes

Abstract

The present study investigated the operational conditions for different pretreatment approaches and subsequent enzymatic hydrolysis of cauliflower wastes (stalk and leaf) for better release of fermentable sugars. The structural analysis of raw and pretreated lignocellulosic biomasses was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transforms infrared (FTIR) analysis. Results demonstrated that the highest cellulose conversion rate and removal of most of the hemicellulose and lignin were obtained with organosolvent pretreatment. Using methanol in presence of sodium (Na) acetate was most effective in delignification of cauliflower wastes. In the present study, methanol (100% v/v) in presence of 0.1?M Na-acetate at 121?°C for 45 and 60?min for stalk and leaf, respectively, gave maximum reducing sugar yield. Response surface methodology was used to optimize different process parameters for enzymatic saccharification using microbial cellulase and xylanase. The optimum operation condition of enzymatic hydrolysis of organosolvent pretreated cauliflower wastes were substrate loading (2.5% w/v for both stalk and leaf), enzyme loading (15 and 10?U/g for stalk and leaf, respectively), pH (4.46 and 5.48 for stalk and leaf, respectively), at 60?°C and for 180?min.     

Optimization of sugar release from sweet sorghum bagasse following solvation of cellulose and enzymatic hydrolysis using response surface methodology

To release sugars effectively from sweet sorghum bagasse (SSB), a cellulose solvent and organic solvent‐based lignocellulose fractionation pretreatment approach was studied using response surface methodology (RSM). Based on RSM's central composite design, a batch experimental matrix was set up to determine the effects of reaction time (20–60 min) and temperature (40–60 °C) on delignification, total reducing sugar yield, glucan digestibility, and overall glucose yields following a pretreatment‐hydrolysis process. The optimum pretreatment conditions of 50 °C and 40 min led to 51.4% delignification, 86% overall glucose yield, and 61% overall xylose yield. An effort has also been made to obtain predictive models to illustrate the correlation between independent and dependent variables using RSM. The significance of the correlations and adequacy of these models were statistically tested for the selected objective functions. The optimum pretreatment condition predicted by the model was 49.1 °C and 39.2 min which matched the experimental data well. Results from this study can be applied to large scale biorefineries using sugars released from SSB for producing various biofuels. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:367–375, 2014     

Statistical optimization of medium components and growth conditions by response surface methodology to enhance lipase production by Aspergillus carneus

A response surface approach has been used to study the production of an extracellular lipase from Aspergillus carneus, which has the property of immense industrial importance. Interactions were studied for five different variables (sunflower oil, glucose, peptone, agitation rate and incubation period), which were found influential for lipase production by one-at a time method. We report a 1.8-fold increase in production, with the final yield of 12.7 IU/ml in comparison to 7.2 U/ml obtained by one-at-a-time method. Using the statistical approach (response surface methodology (RSM)) the optimum values of these most influential parameters were as follows: sunflower oil (1%), glucose (0.8%), peptone (0.8%), agitation rate (200 rpm) and incubation period (96 h) at 37 °C. The subsequent verification experiment confirmed the validity of the model.     

Effect of peracetic acid, sodium hydroxide and phosphoric acid on cellulosic materials as a pretreatment for enzymatic hydrolysis

Crystalline cellulose and cellulosic wastes have been treated with various concentrations of peracetic acid and other reagents at 100°C for various times, washed with water, ethanol and air dried. For each treated cellulose, the degree of enzymatic solubilization was measured with Trichoderma viride cellulase [1,4-(1,3;1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4]. Cellulosic wastes such as sunflower stalks, wheat straw and sugar-cane bagasse were solubilized effectively by the enzyme. Delignification of wheat straw with 1% sodium hydroxide and treatment of this straw with peracetic acid enhanced the degree of enzymatic solubilization. Infrared spectra of the untreated and treated cellulosic wastes were recorded.     

Effect of biological pretreatment with Trametes hirsuta yj9 on enzymatic hydrolysis of corn stover

In this study, a newly isolated Trametes hirsuta yj9 was used to pretreat corn stover in order to enhance enzymatic digestibility. T. hirsuta yj9 preferentially degraded lignin to be as high as 71.49% after 42-day pretreatment. Laccase and xylanase was the major ligninolytic and hydrolytic enzyme, respectively and filter paper activity (FPA) increased gradually with prolonged pretreatment time. Sugar yields increased significantly after pretreatment with T. hirsuta yj9, reaching an enzymatic digestibility of 73.99% after 42 days of pretreatment. Scanning electron microscopy (SEM) showed significant structural changes in pretreated corn stover, the surface of pretreated corn stover became increasingly coarse, the gaps between cellulose fibers were visible, and many pores were developed. Correlation analysis showed that sugar yields were inversely proportional to the lignin contents, less related to cellulose and hemicellulose contents.     

Optimization of extraction technology of Astragalus polysaccharides by response surface methodology and its effect on CD40

Astragali is a herbal medicine used as an adjuvant extensively in the treatment of various cancers of lung, digestive tract, urinary system, etc. Statistics-based experimental designs were applied to optimize the extraction conditions for Astragalus polysaccharides (AP). The optimum conditions were found to be: the values of extraction time 3 h, ratio of liquid to solid 4 and particle size 33.8 mesh. Under these optimized conditions, the maximum AP extraction rate was 16.32 (%), which well matches with the predicted value. Furthermore, the chemical composition was analyzed with HPLC, and the pharmacological effect of the AP was evaluated. Results showed that AP could significantly decreased CD40 expression rate and protein expression in rats with stomach cancer.     

Effect of pretreatment severity on the conversion of barley straw to fermentable substrates and the release of inhibitory compounds

The production of fermentable substrates from barley straw under various process conditions was studied. Pretreatment included chemical pretreatment with dilute-acid followed by enzymatic hydrolysis; the pretreatment conditions were expressed in a combined severity factor, CS, which ranged in the present study from −1.6 to 1.1. Considering the production of fermentable sugars and the release of inhibitory compounds, the optimal pretreatment conditions were 170 °C, 0% sulfuric acid and 60 min, corresponding to CS −0.4. Under these conditions, 21.4 g glucose/L, 8.5 g xylose/L, and 0.5 g arabinose/L were produced, while 0.1 g HMF/L, 0.4 g furfural/L, 0.0 g levulinic acid/L, 0.0 g formic acid/L, and 2.1 g acetic acid/L were released. The ratio of Σsugars/Σinhibitors proved to be a good tool for evaluating the suitability of a hydrolysate for fermentation purposes.     

Effect of system variables involved in packed column SFC of nevirapine as model analyte using response surface methodology: application to retention thermodynamics, solute transfer kinetic study and binary diffusion coefficient determination

A multifactor optimization technique is successfully applied to study the effect of simultaneously varying the system variables on feasibility of nevirapine analysis by packed column supercritical fluid chromatography (PC-SFC). The optimal conditions were determined with the aid of the response surface methodology using 3(3) factorial designs. The method is based on methanol-modified carbon dioxide as the mobile phase at flow rate of 3.0 ml/min with elution through a JASCO Finepak SIL-5, [C18 (5-micron, 25 cm x 4.6 mm, i.d.)] column using photodiode array detection. The method has been successfully used to analyze commercial solid dosage form to assess the chromatographic performance of SFC system. The present work briefs the thermodynamic applications of PC-SFC with an emphasis on the results of nevirapine. The foremost of such applications is the determination of solute diffusion coefficient in supercritical mobile phase by Taylor-Aris peak broadening technique.