Kinetic Studies on the Product Inhibition of Enzymatic Lignocellulose Hydrolysis

Preparation and characterization of bacterial cellulose synthesized by kombucha from vinegar residue

Bacterial cellulose (BC) has been widely applied in various fields due to its excellent physicochemical properties, but its high production cost remains a challenge. Herein, the present study aimed to utilize the hydrolysate of vinegar residue (VR) as the only medium to realize the cost-effective production of BC. The BC production was optimized by the single-factor test. The treatment of 6 % VR concentration with 3 % acid concentration at 100 °C for 1.5 h and 96 U/mL of cellulase for 4 h at 50 °C obtained a maximum reducing sugar concentration of about 32 g/L. Additionally, the VR hydrolysate treated with 3 % active carbon (AC) at 40 °C for 0.5 h achieved a total phenol removal ratio of 86 %. The yield of BC reached 2.1 g/L under the optimum conditions, which was twice compared to the standard medium. The produced BC was characterized by SEM, FT-IR, XRD, and TGA analyses, and the results indicated that the BC prepared by AC-treated VR hydrolysate had higher fiber density, higher crystallinity, and good thermal stability. Furthermore, the regenerated BC (RBC) fibers with a tensile stress of 400 MPa were prepared successfully using AmimCl solution as a solvent by dry-wet-spinning method. Overall, the VR waste could be used as an alternative carbon source for the sustainable production of BC, which could be further applied to RBC fibers preparation.

Kinetic Model for Enzymatic Hydrolysis of Cellulose from Pre-Treated Rice Husks

Rice husks contain cellulose as a raw material for manufacturing second-generation bioethanol. Cellulose from pre-treated rice husks was converted into reducing sugars through enzymatic hydrolysis using enzymes derived from Aspergillus niger. This study aims to determine the kinetics of enzymatic hydrolysis at enzyme concentrations of 10, 15, and 20% (v/w) and hydrolysis times of 5, 10, 15, 20, and 25 h. The results showed that cellulose was hydrolyzed to form reducing sugars. The CMCase activity and FPase activity reached 548.940 and 314.892 U mL−1, respectively, much higher than most previous reports on this genus. From the calculation of the reaction rate using the Michaelis–Menten kinetic model, the value of the Michaelis constant ranges from 0.001 to 0.0007, and the maximum rate is 1.3 × 10−7 to 2.7 × 10−7 Mol L−1 s−1. The highest reducing sugar concentration was obtained (1.80 g L−1) at an enzyme concentration of 20% (v/w) and a hydrolysis time of 25 h.

Enzymatic hydrolysis of beech wood lignocellulose at high solid contents and its utilization as substrate for the production of biobutanol and dicarboxylic acids

The development of a cost-effective hydrolysis for crude cellulose is an essential part of biorefinery developments. To establish such high solid hydrolysis, a new solid state reactor with static mixing is used. However, concentrations >10% (w/w) cause a rate and yield reduction of enzymatic hydrolysis. By optimizing the synergetic activity of cellulolytic enzymes at solid concentrations of 9%, 17% and 23% (w/w) of crude Organosolv cellulose, glucose concentrations of 57, 113 and 152 g L(-1) are reached. However, the glucose yield decreases from 0.81 to 0.72 g g(-1) at 17% (w/w). Optimal conditions for hydrolysis scale-up under minimal enzyme addition are identified. As result, at 23% (w/w) crude cellulose the glucose yield increases from 0.29 to 0.49 g g(-1). As proof of its applicability, biobutanol, succinic and itaconic acid are produced with the crude hydrolysate. The potential of the substrate is proven e.g. by a high butanol yield of 0.33 g g(-1).

Quantitative full time course analysis of nonlinear enzyme cycling kinetics

Enzyme inhibition due to the reversible binding of reaction products is common and underlies the origins of negative feedback inhibition in many metabolic and signaling pathways. Product inhibition generates non-linearity in steady-state time courses of enzyme activity, which limits the utility of well-established enzymology approaches developed under the assumption of irreversible product release. For more than a century, numerous attempts to find a mathematical solution for analysis of kinetic time courses with product inhibition have been put forth. However, no practical general method capable of extracting common enzymatic parameters from such non-linear time courses has been successfully developed. Here we present a simple and practical method of analysis capable of efficiently extracting steady-state enzyme kinetic parameters and product binding constants from non-linear kinetic time courses with product inhibition and/or substrate depletion. The method is general and applicable to all enzyme systems, independent of reaction schemes and pathways.