Optimized Bioconversion of Xylose Derived from Pre-Treated Crop Residues into Xylitol by Using Candida boidinii

Crop residues can serve as low-cost feedstocks for microbial production of xylitol, which offers many advantages over the commonly used chemical process. However, enhancing the efficiency of xylitol fermentation is still a barrier to industrial implementation. In this study, the effects of oxygen transfer rate (OTR) (1.1, 2.1, 3.1 mmol O2/(L × h)) and initial xylose concentration (30, 55, 80 g/L) on xylitol production of Candida boidinii NCAIM Y.01308 on xylose medium were investigated and optimised by response surface methodology, and xylitol fermentations were performed on xylose-rich hydrolysates of wheat bran and rice straw. High values of maximum xylitol yields (58–63%) were achieved at low initial xylose concentration (20–30 g/L) and OTR values (1.1–1.5 mmol O2/(L × h)). The highest value for maximum xylitol productivity (0.96 g/(L × h)) was predicted at 71 g/L initial xylose and 2.7 mmol O2/(L × h) OTR. Maximum xylitol yield and productivity obtained on wheat bran hydrolysate were 60% and 0.58 g/(L × h), respectively. On detoxified and supplemented hydrolysate of rice straw, maximum xylitol yield and productivity of 30% and 0.19 g/(L × h) were achieved. This study revealed the terms affecting the xylitol production by C. boidinii and provided validated models to predict the achievable xylitol yields and productivities under different conditions. Efficient pre-treatments for xylose-rich hydrolysates from rice straw and wheat bran were selected. Fermentation using wheat bran hydrolysate and C. boidinii under optimized condition is proved as a promising method for biotechnological xylitol production.

Removal of fermentation inhibitors from pre-hydrolysis liquor using polystyrene divinylbenzene resin

Background The presence of soluble lignin, furfural and hydroxymethylfurfural (HMF) in industrial pre-hydrolysis liquor (PHL) from the pulping process can inhibit its bioconversion into bioethanol and other biochemicals. Although various technologies have been developed to remove these inhibitors, certain amounts of sugars are also inevitably removed during the treatment process. Hence, polystyrene divinylbenzene (PS-DVB) resin was used as an adsorptive material to simultaneously remove fermentation inhibitors while retaining sugars with high yields to improve the fermentability of PHL after acid hydrolysis by enriching its xylose concentration. The fermentability of acid-hydrolyzed PHL (A-PHL) was evaluated by the bioconversion into ethanol and xylosic acid (XA) after treatment with PS-DVB resin. Results The results showed that the highest xylose concentration (101.1 g/L) in PHL could be obtained by acid hydrolysis at 100 °C for 80 min with 4% acid, while the concentration of fermentation inhibitors (furfural, HMF and lignin) in PHL could also be significantly improved during the acid-hydrolysis process. After treatment with PS-DVB resin, not only were 97% of lignin, 92% of furfural, and 97% of HMF removed from A-PHL, but also 96% of xylose was retained for subsequent fermentation. With resin treatment, the fermentability of A-PHL could be improved by 162–282% for ethanol production from A-PHL containing 30–50 g/L xylose and by 18–828% for XA production from A-PHL containing 90–150 g/L xylose. Conclusions These results confirmed that PS-DVB resin can remove inhibitors from PHL before producing value-added products by bioconversion. In addition, this work will ideally provide a concept for producing value-added chemicals from pre-hydrolysis liquor, which is regarded as the waste stream in the pulping process.

Chemical Free Two-Step Hydrothermal Pretreatment to Improve Sugar Yields from Energy Cane

Energy cane is an attractive lignocellulosic feedstock for processing into biofuels and bioproducts. A low-severity two-step hydrothermal pretreatment was investigated on energy cane for the production of monomeric sugar. Pretreatment temperature and time, in addition to the effect of disk milling, were observed for the glucose and xylose yields during hydrolysis. At residence times above 5 min in case of pretreatment at 200 °C, all of the hemicellulose was observed to be solubilized. The pretreatment condition of 200 °C for 10 min with disk milling was observed to provide the highest glucose concentration of 5.4%, and 200 °C for 5 min with disk milling provided the highest xylose concentration of 2.15%. The effect of disk milling in improving the sugar concentrations during hydrolysis was significant, especially at lower pretreatment temperatures and times. Low xylose yields at higher temperatures were attributed to the formation of degradation products at increased severity.

Removal of fermentation inhibitors from pre-hydrolysis liquor using polystyrene divinylbenzene resin

Background: The presence of soluble lignin, furfural and hydroxymethylfurfural (HMF) in industrial pre-hydrolysis liquor (PHL) from the pulping process can inhibit its bioconversion into bioethanol and other biochemicals. Although various technologies have been developed to remove these inhibitors, certain amounts of sugars are also inevitably removed during the treatment process. Hence, polystyrene divinylbenzene (PS-DVB) resin was used as an adsorptive material to simultaneously remove fermentation inhibitors while retaining sugars with high yields to improve the fermentability of PHL after acid-hydrolysis by enriching its xylose concentration. The fermentability of acid-hydrolyzed PHL (A-PHL) was evaluated by the bioconversion into ethanol and xylosic acid (XA) after treatment with PS-DVB resin.Results: The results showed that the highest xylose concentration (101.1 g/L) in PHL could be obtained by acid-hydrolysis at 100 oC for 80 min with 4% acid, while the concentration of fermentation inhibitors (furfural, HMF and lignin) in PHL could also be significantly improved during the acid-hydrolysis process. After treatment with PS-DVB resin, not only were 97% of lignin, 92% of furfural, and 97% of HMF removed from A-PHL, but also 96% of xylose was retained for subsequent fermentation. With resin treatment, the fermentability of A-PHL could be improved by 162-282% for ethanol production from A-PHL containing 30-50 g/L xylose and by 18-828% for XA production from A-PHL containing 90-150 g/L xylose. Conclusions: These results confirmed that PS-DVB resin can remove inhibitors from PHL before producing value-added products by bioconversion. In addition, this work will ideally provide a concept for producing value-added chemicals from pre-hydrolysis liquor, which is regarded as the waste stream in the pulping process.

Improving the fermentability of pre-hydrolysis liquor to produce ethanol and xylonic acid by removing fermentation inhibitors using polystyrene divinylbenzene resin

Background The existences of soluble lignin, furfural and HMF in industrial pre-hydrolysis liquor (PHL) can inhibit its bioconversion into bioethanol and other bio-chemicals. Although various technologies have been carried out to remove these inhibitors, a undesirable sugars removal is also happened during the process. Hence, polystyrene divinylbenzene (PS-DVB) resin was used as adsorptive material to simultaneously remove fermentation inhibitors while retain sugars with higher yield for improving the fermentability of PHL after acid-hydrolysis (A-PHL) treatment. The fermentability of treated PHL was evaluated by the bioconversion into ethanol and xylosic acid (XA). Results Results showed that an highest xylose concentration (101.1 g/L) in PHL could be obtained by acid-hydrolysis at 100 oC for 80 min with 4% acid, while concentration of fermentation inhibitors (furfural, HMF and lignin) could also be significantly improved. After treating, not only 97% of lignin, 92% of furfural, and 97% of HMF were removed from solution, but also 96% of xylose was retained for subsequent fermentation. With resin treatment, the fermentability of A-PHL could be improved by 162–282% for ethanol production from A-PHL with 30–50 g/L xylose and by 18–828% for XA production from A-PHL with 90–150 g/L xylose. Conclusions These results confirmed that PS-DVB resin can remove inhibitors from PHL before producing value-added products by bioconversion. In addition, the work will ideally provide a concept by which pulping facilities could go about producing value-added chemicals from existing waste streams.

Fiber degrading enzymes increased monosaccharides release and fermentation in corn distillers dried grains with solubles and wheat middlings steeped without or with protease

Treating fibrous feed ingredients with exogenous feed enzymes may improve their utilization in monogastric animals. An in vitro study was conducted to determine the effects of steeping corn distillers dried grains with solubles (DDGS) or wheat middlings (WM) with exogenous feed enzymes. Four treatments were arranged as follows: 1) co-product steeped with water (CON), 2) CON plus 0.5-g fiber degrading enzymes (FDE), 3) CON plus 0.5-g protease (PRO), and 4) CON plus 0.5-g FDE and 0.5 g PRO (FDEPRO). The FDE contained about 62,000, 37,000, and 8,000 U/g of xylanase, cellulase, and β-glucanase, respectively, whereas activities in PRO amounted to 2,500,000, 1,300,000, and 800,000 U/g of acid, alkaline, and neutral proteases, respectively. Briefly, 50 g of DDGS or WM samples (n = 8) were mixed with 500-mL water with or without enzymes and steeped for 0 to 72 h at 37 °C with continuous agitation. The pH, concentration of monosaccharides, and organic acids in the supernatant and apparent disappearance (AD) of fiber in solids were measured at 0, 12, 24, 48, and 72 h. There was treatment and time interaction (P < 0.005) on monosaccharides concentration. At 12 h, arabinose and glucose concentrations were similar (P > 0.05) between FDE and FDEPRO but higher (P = 0.002) than for CON in DDGS. For WM, FDE, and FDEPRO had higher (P < 0.001) xylose concentration than CON and PRO, whereas glucose concentration was higher (P < 0.001) for enzymes than CON at 12 h. However, FDEPRO had higher (P < 0.001) xylose concentration than CON, whereas xylose concentration for FDE and PRO was intermediate at 24 h. There was an interaction (P < 0.05) between treatment and time effect on lactic acid concentration in DDGS and WM (P < 0.005), and acetic acid concentration in WM (P < 0.001). In general, monosaccharide concentration was higher between 12 and 24 h and decreased after 48 h, whereas the pH decreased, and concentration of organic acids increased continuously over time (P < 0.05). The AD of NDF and ADF in DDGS was greater (P = 0.001) for FDE and FDEPRO than CON and PRO at 72 h. In WM, enzymes increased (P = 0.007) AD of NDF relative to CON at 72 h. Nonetheless, greater (P < 0.05) AD of fiber was observed between 48 and 72 h. In conclusion, although there were differences in responses among co-products, fiber degrading enzymes increased release of fermentable monosaccharides from co-products at 12 to 24 h of steeping and these effects were not extended with the addition of protease.

Combined Treatments Consisting of Calcium Hydroxide and Activate Carbon for Purification of Xylo-Oligosaccharides of Pre-Hydrolysis Liquor

In this study, the effect of a combined treatment consisting of calcium hydroxide (CH) followed by activated carbon (AC) on the purification of hemicellulose in the pre-hydrolysis liquor (PHL) from pulping process has been evaluated. The results show that lignin and furfural of PHL are efficiently removed, and the lignin removal is achieved by forming complexes onto CH particles in the CH treatment process, while acetic acid (acetate) is formed from the hydrolysis of acetyl groups present in the dissolved hemicelluloses in the PHL. The loss of xylo-oligosaccharides (XOS) is moderate, even at a high CH dosage of 0.8% while the xylose concentration is essentially unchanged. For the AC treatment, the optimal treating pH can enhance the interactions between AC and residual lignin and change the zeta potential of AC resulting in improved lignin adsorption onto AC. An increase of AC dosage has the tendency to adsorb more XOSDP>6 than XOSDP2~6. Overall, 66.9% of lignin and 70.1% of furfural removals are achieved under the optimal conditions of CH and AC treatment process, with a 5.9% total xylosugars loss. The present combination of CH and AC treatment process was more effective and selective for purification of xylosugars of PHL.

Conversion of hemicellulose from kenaf core fiber to xylose through dilute sulfuric acid hydrolysis

Kenaf (Hibiscus cannabinus) is a lignocellulosic plant that is usually utilized as a fiber source for sack production. The core from kenaf fiber has not been utilized yet in Indonesia, therefore it is still considered as a waste. Hemicellulose from kenaf core can be hydrolyzed to xylose through dilute sulfuric acid hydrolysis in high temperature. Hydrolysis in this study was done by using autoclave at 121℃ and 10% (m/v) biomass: acid ratio for 15 and 45 minutes with a variation on acid concentration (2%, 4%, and 6% v/v). Xylose concentration in the hydrolyzate tends to increase with higher acid concentration and longer heating time. 6% (v/v) sulfuric acid concentration and 45 minutes of heating time produce the highest xylose concentration (20.53 gr/L) and yield (86.50%)