Effect of alkali-treated birch sawdust on the lignocellulase secretion and exo-polysaccharide production by Inonotus obliquus under submerged fermentation and its lignocellulose degradation patterns.

The objectives of this study were to investigate the medicinal mushroom Inonotus obliquus on the production of polysaccharides and changes of extracellular lignocellulolytic enzymes during submerged fermentation using alkali-treated birch sawdust as substrate. Meanwhile, in order to explore the degradation mode of lignocellulose in alkali-treated birch sawdust, degradation analysis of three components of lignocellulose was carried out. The fungus process in alkali-treated birch sawdust medium resulted in a higher degradation rate of cellulose, hemicellulose, and lignin of 39.24%, 51.00% and 31.3% after 11 days of submerged fermentation by the mycelium of I. obliquus, respectively. Maximal polysaccharide production and α-glucosidase inhibition rate determined in the alkali-treated birch sawdust medium were 6.93 mg/mL and 55.80%, while they were 4.98 mg/mL and 27.89% in the control. Moreover, high activities of laccase (51.95 IU/mL), CMCase (1.35 IU/mL), filter paper activity (0.50 IU/mL) and ß-glucosidase (0.55 IU/mL) were observed in alkali-treated birch sawdust medium, respectively. The results demonstrated that the addition of alkali-treated birch sawdust could promote the yield and α-glucosidase inhibition activity of polysaccharides and induce the production of cellulase and xylanase, indicating that alkali pretreatment was conducive to utilization of birch sawdust by I. obliquus.

Effect of Different Pretreatment of Birch Sawdust on the Production of Active Polysaccharides by Inonotus obliquus Under Submerged Fermentation and Its Structural Mechanism.

This study examined the effects of different pretreatments of birch sawdust on the production and activity of polysaccharides by Inonotus obliquus, and in order to explore the mechanism, structural characterization and analysis were carried out. The result clearly indicated that alkali treatment, ozone treatment, and alkali combined with ozone treatment of birch sawdust could be all helpful for the production of active polysaccharide by I. obliquus. Among four pretreatment groups, birch sawdust treated with alkali showed the highest increase in the exo-polysaccharide content (39.90%) and the inhibition rate of α-glucosidase (80.78%) within 11 days by the mycelium of I. obliquus through deep fermentation, in comparison to water-washed birch sawdust. Through a single-factor analysis and orthogonal experimental design, the optimum alkali treatment condition was as follows: NaOH concentration 1%, temperature 60 °C, and time 3 h. Moreover, the structural characteristics of pretreated birch sawdust with the optimum alkali treatment condition before and after fermentation by the mycelium of I. obliquus was performed by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electronic microscopy. The results showed that alkali treatment destroyed the lignin structure of birch sawdust, exposed the cellulose in the amorphous area, reduced the crystallinity of lignocellulose, and damaged the surface structure of birch sawdust, which had a further damage and a greater degradation degree of birch sawdust after fermentation, indicating that alkali pretreatment was beneficial for utilization of birch sawdust by I. obliquus.

Effects and Mechanisms of Alkali Recycling and Ozone Recycling on Enzymatic Conversion in Alkali Combined with Ozone Pretreatment of Corn Stover.

In order to minimize waste liquor, save resources, and reduce costs, the effects of alkali recycling and ozone recycling on enzymatic conversion in alkali combined with ozone pretreatment of corn stover and the mechanism were studied. The results showed that as the number of cycles of alkali/ozone filtrate increased, the enzymatic conversion and the loss of reducing sugars showed a downward trend. It was indicated that the ability of alkali to damage lignocellulosic decreased with an increasing number of alkali circulation and the accumulation of lignin degradation products generated during ozonolysis inhibited enzymatic conversion. When the ozone filtrate was recovered and used for hydrolysis directly, the enzymatic conversion rates were basically the same compared with the first self-circulation of ozone filtrate, and no sewage was discharged. In conclusion, the optimal circulating pretreatment was four times alkali circulation and ozone filtrate was used as an enzymolysis liquid directly, and the conversion rates of cellulose and hemicellulose were 85.96% and 34.26%, respectively, saving 44% alkali consumption at the same time. This paper provided the theoretical basis for the development of lignocellulose pretreatment technology with low cost, high efficiency, and high conversion rate.

Adsorption Study of Lignin Removal from Recycled Alkali Black Liquor by Adsorption Resins for Improved Cellulase Hydrolysis of Corn Straw.

Previous studies showed that aromatic compounds such as lignin, phenols, and furans were main inhibitors of cellulase hydrolysis in recycled alkali black liquor (RBL), which should be removed to improve alkali utilization. In this study, three polymeric resins, XAD-4, XAD-16N, and XAD-7HP, were evaluated for their abilities to remove lignin from alkali black liquor recycled at the third time. Adsorption conditions of adsorbent dose and equilibrium time, isotherms, and kinetics were investigated. Of three tested adsorbents, XAD-16N was the most efficient, which can remove 89.84% of lignin after adsorption at an adsorbent-to-solution ratio of 1:4 for 2.5 h. Pseudo-second-order model was efficient to represent XAD-16N and XAD-7HP adsorption kinetics. Adsorption behavior of XAD-4 on RBL was fitted better to Langmuir model, while XAD-16N and XAD-7HP adsorption were more consistent with Freundlich model. The cellulase hydrolysis rate of corn straw treated with RBL after XAD-16N adsorption combined with ozone was 86.89%, which was only 0.89% lower than that of sodium hydroxide combined with ozone treatment. Structure characterization proved that the damage of XAD-16N adsorbed RBL to corn straw was similar to that of sodium hydroxide. It indicated that adsorption was effective in inhibitor removal from RBL to improve alkali utilization.

Simultaneous Use of Stimulatory Agents to Enhance the Production and Hypoglycaemic Activity of Polysaccharides from Inonotus obliquus by Submerged Fermentation.

This study aimed to determine the effect of applying stimulatory agents to liquid cultured Inonotus obliquus on the simultaneous accumulation of exo-polysaccharides (EPS) and their monosaccharide composition. Different stimulatory agents (VB6, VB1, betulin and birch extract) were investigated for their effects on active exo-polysaccharides by submerged fermentation of I. obliquus. The mycelial biomass, reducing sugar content, EPS yield and α-glucosidase inhibition rate were determined, and the EPS obtained was analyzed for monosaccharide composition. The results showed that the addition of all the four stimulatory agents could significantly increase the inhibitory activity against α-glucosidase of EPS than the control, whereas EPS from 4 µg/mL VB1-containing medium had the best effect with an estimated IC50 value 24.34 µg/mL. Among the four stimulatory agents, VB6 gave maximum production of mycelial biomass and EPS at the concentration of 4 µg/mL with a increase of 50.79% and 114.46%, respectively. In addition, betulin had a significant effect on increasing the EPS yield and activity, and birch extract had a significantly stimulatory effect on the mycelial growth and the polysaccharides activity, only slightly worse than VB6 and VB1. Moreover, the addition of different stimulatory agents changed the monosaccharide composition of polysaccharides, which had a correlation with polysaccharide activity.