Process optimization for the pretreatment of rice husk with deep eutectic solvent for efficient sugar production.

ABSTRACTDeep eutectic solvent (DES) has been identified as a potential green solvent in biomass processing. In the present investigation, a deep eutectic solvent i.e. choline chloride: urea (ChCl/U) was synthesized and employed to pretreat rice husks. Plackett- Burman response surface methodology was used to optimize the factors which are DES molar ratio, residence time, temperature, and biomass concentration. A total of 11 experimental conditions were evaluated and the highest amount of reducing sugar was obtained when 2 g rice husk was pretreated with 1:2 ChCl/U at 80°C for 6 h i.e. 0.67 ± 0.05 mg/mL. Furthermore, scanning electron microscopy (SEM), Fourier transforms infrared (FTIR), and X-ray diffraction (XRD) studies were used to characterize the structural and compositional changes in which DES demonstrates a great performance in the pretreatment of rice husk by eliminating amorphous lignin and hemicellulose content. Therefore, the facile process used in this study has the potential to be used on a massive scale to produce fermentable sugars and other compounds.

Kinetic modeling and statistical optimization of submerged production of anti-Parkinson's prodrug L-DOPA by Pseudomonas fluorescens.

L-DOPA, a precursor of dopamine, is the drug of choice for Parkinson's disease, which persists due to decreased levels of dopamine in the brain. Present study emphasis the microbial production of L-DOPA rather than the biotransformation of L-DOPA by L-tyrosine. The production of L-DOPA by bacterial isolates had gained more acceptance due to its more straightforward extraction and downstream processes. Pseudomonas fluorescens was used to produce the L-DOPA in a bioreactor system under submerged condition. The design of experiment-based Taguchi orthogonal array method was adopted for the optimization of production. L-9 orthogonal array using the analysis of mean approach was used to study the effect of different factors viz NaCl, lactose, tryptone, and inducer on the microbial production of L-DOPA. The method mentioned above is less time consuming and does not require any harsh chemicals, proving it to be an eco-friendly process. After optimizing selected factors, i.e., NaCl (1.2 g/l), lactose (1.5 g/l), tryptone (4 g/l), and inducer (0.1 g/l), 16.9 % of enhancement in L-DOPA production with 66.6% of process cost saving was observed. The production of L-DOPA was increased from 3.426 ± 0.08 g/l to 4.123 ± 0.05 g/l after optimization. Subsequently, unstructured kinetic models were adopted to simulate the fermentation kinetics and understand the metabolic process. Fisher' F test and determination coefficients (R2) confirmed that the Velhurst-Pearl logistic equation, Luedeking-Piret equation, and modified Luedeking-Piret equation was best fitted with the biomass production, product formation, and substrate utilization, respectively.