Optimization of sodium percarbonate pretreatment for improving 2,3-butanediol production from corncob.

Sodium percarbonate (SP), a kind of alkaline strong oxidant, was applied to corncob pretreatment. The optimized pretreatment conditions were at 4% (w/v) SP concentration with solid-to-liquid (SLR) ratio of 1:10 treating for 4 hr at 60°C. This pretreatment resulted in 91.06% of cellulose and 84.08% of hemicellulose recoveries with 34.09% of lignin removal in corncob. The reducing sugar yield from SP-pretreated corncob was 0.56 g/g after 72 hr of enzymatic hydrolysis, 1.75-folds higher than that from raw corncob. 2,3-butanediol production by Enterobacer cloacae in simultaneous saccharification fermentation was 29.18 g/L using SP-pretreated corncob as a substrate, which was 11.12 times of that using raw corncob. Scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectra analysis indicated that physical characteristics, crystallinity, and structure of corncob had changed obviously after SP pretreatment. This simple and novel pretreatment method was effective for delignification and carbohydrate retention in microbial production of 2,3-butanediol from lignocellulose biomass.

Effect of ß-mannanase domain from Trichoderma reesei on its biochemical characters and synergistic hydrolysis of sugarcane bagasse.

BACKGROUND: ß-mannanase is a key enzyme for hydrolyzing mannan, a major constituent of hemicellulose, which is the second most abundant polysaccharide in nature. Different structural domains greatly affect its biochemical characters and catalytic efficiency. However, the effects of linker and carbohydrate-binding module (CBM) on ß-mannanase from Trichoderma reesei (Man1) have not yet been fully described. The present study aimed to determine the influence of different domains on the expression efficiency, biochemical characteristics and hemicellulosic deconstruction of Man1. RESULTS: The expression efficiency was improved after truncating CBM. Activities of Man1 and Man1ΔCBM (CBM) in the culture supernatant after 168 h of induction were 34.5 and 42.9 IU mL-1 , although a value of only 0.36 IU mL-1 was detected for Man1ΔLCBM (lacking CBM and linker). Man1 showed higher thermostability than Man1ΔCBM at low temperature, whereas Man1ΔCBM had a higher specificity for galactomannan (Km = 2.5 mg mL-1 ) than Man1 (Km = 4.0 mg mL-1 ). Both Man1 and Man1ΔCBM could synergistically improve the hydrolysis of cellulose, galactomannan and pretreated sugarcane bagasse, with a 10-30% improvement of the reducing sugar yield. CONCLUSION: Linker and CBM domains were vital for mannanase activity and expression efficiency. CBM affected the thermostability and adsorption ability of Man1. The results obtained in the present study should help guide the rational design and directional modification of Man with respect to improving its catalytic efficiency. © 2017 Society of Chemical Industry.

Simultaneous determination of furfural, acetic acid, and 5-hydroxymethylfurfural in corncob hydrolysates using liquid chromatography with ultraviolet detection.

A single-laboratory validation study was conducted using HPLC for detecting and quantifying acetic acid, furfural, and 5-hydroxymethylfurfural (HMF) in corncob hydrolysates. A pretreatment procedure using dilute sulfuric acid was optimized for corncob hydrolysis. The final hydrolysates were analyzed by HPLC using a C18 RP column with aqueous 0.01% (v/v) H2SO4-CH3OH (95 + 5) as the mobile phase at a flow rate of 1 mL/min. The wavelengths for detecting the three compounds were changed to their optimal UV detection wavelengths at the time of elution. The wavelength detection adjustments were as follow: 205 nm (0 to 4 min); 284 nm (4 to 7 min); and 276 nm (7 to 10 min). Separation was achieved with a chromatographic run time of 10 min. The calibration curves for the three compounds had correlation coefficients (r2) > or = 99.8%. The analytical range, as defined by the calibration curves, was 0.5-10 mg/L for acetic acid, 0.4-22 mg/L for furfural, and 0.1-18 mg/L for HMF. The LODs for acetic acid, furfural, and HMF were estimated to be 0.05, 0.03, and 0.02 mg/L, respectively; the LOQs were 0.196, 0.135, and 0.074 mg/L, respectively. The RSD values for the intraday precision study ranged from 0.31 to 2.22%, and from 0.57 to 2.43% for the interday study. The mean recovery rates in all compounds were between 100.08 and 101.49%.

Efficient utilization of hemicellulose and cellulose in alkali liquor-pretreated corncob for bioethanol production at high solid loading by Spathaspora passalidarum U1-58.

The bioethanol fermentation of pretreated corncob was investigated using Spathaspora passalidarum U1-58, which simultaneously utilizes glucose and xylose for high-efficiency ethanol production. Two approaches, namely, separate hydrolysis and co-fermentation (SHCF) and simultaneous saccharification and co-fermentation (SSCF), were optimized to test the ethanol fermentation potential of U1-58. The highest ethanol titer of 42.46g/L and yield of 72.12% were acquired in SHCF, whereas 53.24g/L ethanol and yield of 75.35% were obtained in SSCF at solid-to-liquid ratio of 1:5 (w/v). Approximately 86.20% of cellulose and 82.99% of hemicellulose were consumed in SSCF after 96h, and at least 10.49g/L ethanol was produced from hemicellulose, which corresponded to 37.59% of the theoretical yield. Compared with the published cellulosic ethanol fermentation cases, the present work presented high ethanol titer and yield, and cellulose and hemicellulose could be efficiently utilized for ethanol production.

Optimization and evaluation of alkaline potassium permanganate pretreatment of corncob.

Alkaline potassium permanganate solution (APP) was applied to the pretreatment of corncob with a simple and effective optimization of APP concentration, reaction time, temperature and solid to liquid ratio (SLR). The optimized pretreatment conditions were at 2% (w/v) potassium permanganate with SLR of 1:10 treating for 6h at 50°C. This simple one-step treatment resulted in significant 94.56% of the cellulose and 81.47% of the hemicellulose recoveries and 46.79% of the lignin removal of corncob. The reducing sugar in the hydrolysate from APP-pretreated corncob was 8.39g/L after 12h enzymatic hydrolysis, which was 1.44 and 1.29 folds higher than those from raw and acid pretreated corncobs. Physical characteristics, crystallinity and structure of the pretreated corncob were analyzed and assessed by SEM, XRD and FTIR. The APP pretreatment process was novel and enhanced enzymatic hydrolysis of lignocellulose by affecting composition and structural features.

Optimization of headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry for detecting methoxyphenolic compounds in pu-erh tea.

A method based on headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was developed for the analysis of volatile methoxyphenolic compounds in pu-erh tea. Six fibers with different polarities were initially evaluated. The 75 µm carboxen/polydimethylsiloxane fiber exhibited the highest extraction efficiency and was selected for further optimization. A Plackett-Burman design was used to screen for the brewing proportion of tea and water, amount of pu-erh tea, ionic strength, extraction time, extraction temperature, desorption time, rate of agitation, and equilibrium time. A Box-Behnken design was then applied to optimize the significant factors. Under optimal conditions, the proposed method affords a wide range of linearity, high linear regression coefficients (0.996-0.999), less than 9.0% repeatability of relative standard deviation, and limits of detection ranging from 2.31 to 21.80 ng/g. The proposed method has satisfactory accuracy, with recoveries of 79.08-113.9%. This method was successfully applied for the analysis of pu-erh tea samples.

Xylose and cellulose fractionation from corncob with three different strategies and separate fermentation of them to bioethanol.

To the aim of efficient utilization of both of xylose and cellulose, a laboratory xylose/cellulose fractionation and separate fermentation (XCFSF) bioethanol process was performed. Three xylose/cellulose fractionation strategies: (A) dilute sulfur acid hydrolysis and detoxification, (B) lime pretreatment and xylanase hydrolysis, (C) bio-treatment with Phanerochaete chrysosporium and xylanase hydrolysis were applied to corn cobs. As a result, the maximum xylose yields obtained from A, B and C fractionation methods were 78.47%, 57.84% and 42.54%, respectively, and 96.81%, 92.14% and 80.34% of cellulose were preserved in the corresponding solid residues. The xylose dissolved in acid and enzymatic hydrolysates was fermented to ethanol by Candida shahatae and the cellulose remaining in solid residues was converted to ethanol by simultaneous saccharification and fermentation (SSF) with Saccharomyces cerevisiae. Finally, for A, B, C fractionation methods, 70.40%, 52.87%, 39.22% of hemicellulose and 89.77%, 84.30%, 71.90% of cellulose in corn cobs was converted to ethanol, respectively.