Using in-situ viscosimetry and morphogranulometry to explore hydrolysis mechanisms of filter paper and pretreated sugarcane bagasse under semi-dilute suspensions

Biochemical limitations of Bacillus thuringiensis based biopesticides production in a wheat bran culture medium

Bacillus thuringiensis, a gram-positive sporulating bacteria found in the environment, produces, during its sporulation phase, crystals responsible for its insecticidal activity, constituted of an assembly of pore-forming δ-endotoxins. This has led to its use as a biopesticide, an eco-friendly alternative to harmful chemical pesticides. To minimize production cost, one endemic Bacillus thuringiensis sv. kurstaki (Btk) strain Lip, isolated from Lebanese soil, was cultivated in a wheat bran (WB) based medium (IPM-4-Citrus project EC n° 734921). With the aim of studying the biochemical limitations of Btk biopesticide production in a wheat bran based medium, the WB was sieved into different granulometries, heat treated, inoculated with Btk Lip at flask scale, then filtered and separated into an insoluble and a permeate fractions. Several biochemical analyses, ie. bio performances, starch, elemental composition, total nitrogen and ashes, were then conducted on both fractions before and after culture. On a morphological level, two populations were distinguished, the fine starch granules and the coarse lignocellulosic particles. The biochemical analyses showed that both the raw and sieved WB have a similar proteins content (0.115 g/gdm WB), water content (0.116 g/gdm WB) and elemental composition (carbon: 45%, oxygen: 37%, nitrogen: 3%, hydrogen: 6%, ashes: 5%). The starch content was 17%, 14% and 34% and the fermentable fraction was estimated to 32.1%, 36.1% and 51.1% respectively for classes 2, 3 and 4. Both the elemental composition and Kjeldahl analyses showed that the nitrogen is the limiting nutrient of the culture.

High-solids loading processing for an integrated lignocellulosic biorefinery: Effects of transport phenomena and rheology - A review

This review aims to present an analysis and discussion on the processing of lignocellulosic biomass in terms of biorefinery concept and circular bioeconomy operating at high solids lignocellulosic (above 15% [w/w]) at the pretreatment, enzymatic hydrolysis stage, and fermentation strategy for an integrated lignocellulosic bioprocessing. Studies suggest high solids concentration enzymatic hydrolysis for improved sugars yields and methods to overcome mass transport constraints. Rheological and computational fluid dynamics models of high solids operation through evaluation of mass and momentum transfer limitations are presented. Also, the review paper explores operational feeding strategies to obtain high ethanol concentration and conversion yield, from the hydrothermal pretreatment and investigates the impact of mass load over the operational techniques. Finally, this review contains a brief overview of some of the operations that have successfully scaled up and implemented high-solids enzymatic hydrolysis in terms of the biorefinery concept.

Impact of Particle Size on the Rheological Properties and Amylolysis Kinetics of Ungelatinized Cassava Flour Suspensions

The effect of particle size on enzymatic hydrolysis of cassava flour at subgelatinization temperature was investigated. A multiscale physical metrology was developed to study the evolution of different physical-biochemical parameters: rheology, granulometry, and biochemistry. In this study, four fractions of cassava flour based on the particle sizes under 75 µm (CR075), 75–125 µm (CR125), 125–250 µm (CR250), and 250–500 µm (CR500) were screened for enzymatic hydrolysis effect. The results showed that all cassava flour suspensions exhibited a shear-thinning behavior, and the viscosity increased drastically with the increase of particle size. During hydrolysis, the viscosity reduced slightly and the non-Newtonian behavior became negligible beyond 4 h of the process. The particles size for CR075 and CR125 increased steadily in diameter mean. The samples of CR250 and CR500 showed more fluctuation by first decreasing, followed by increasing in particle sizes during the process. The highest hydrolysis yield was found for samples with particle size under 125 µm (89.5–90.7%), suggesting that mechanical treatment of cassava can enhance the bioconversion rate.

Enzyme-Mediated Lignocellulose Liquefaction Is Highly Substrate-Specific and Influenced by the Substrate Concentration or Rheological Regime

The high viscosities/yield stresses of lignocellulose slurries makes their industrial processing a significant challenge. However, little is known regarding the degree to which liquefaction and its enzymatic requirements are specific to a substrate's physicochemical and rheological properties. In the work reported here, the substrate- and rheological regime-specificities of liquefaction of various substrates were assessed using real-time in-rheometer viscometry and offline oscillatory rheometry when hydrolyzed by combinations of cellobiohydrolase (Trichoderma reesei Cel7A), endoglucanase (Humicola insolens Cel45A), glycoside hydrolase (GH) family 10 xylanase, and GH family 11 xylanase. In contrast to previous work that has suggested that endoglucanase activity dominates enzymatic liquefaction, all of the enzymes were shown to have at least some liquefaction capacity depending on the substrate and reaction conditions. The contribution of individual enzymes was found to be influenced by the rheological regime; in the concentrated regime, the cellobiohydrolase outperformed the endoglucanase, achieving 2.4-fold higher yield stress reduction over the same timeframe, whereas the endoglucanase performed best in the semi-dilute regime. It was apparent that the significant differences in rheology and liquefaction mechanisms made it difficult to predict the liquefaction capacity of an enzyme or enzyme cocktail at different substrate concentrations.

Effects of rice straw structure on chaetoglobosin A production by Chaetomium globosum CGMCC 6882

As the most abundant macromolecules in nature, lignocelluloses are served as a promising and renewable source for sustainable production of high value chemical compounds. In present work, extrusion pretreatment with 23% (w/w) distilled water, 2% (w/w) glycerol and 1 g/L NaHCO₃ as moisture agent, not only reduced the particle size, crystallinity and component contents (cellulose, hemicelluloses and lignin) of rice straw, but also effectively enhanced chaetoglobosin A yield and degradation rate of rice straw by C. globosum CGMCC 6882. Meanwhile, mycelial biomass of C. globosum CGMCC 6882 increased from 2.9 g/L to 7.0 g/L, mycelia growth time reduced by 2 days and chaetoglobosin A titer increased from 108.4 mg/L to 270.2 mg/L, representing an increase of 149.3%. Furthermore, degradation rate of rice straw by C. globosum CGMCC 6882 increased from 28.93% to 65.38%. This work provides a good guidance for production of chaetoglobosin A from lignocelluloses.

Combined in situ Physical and ex-situ Biochemical Approaches to Investigate in vitro Deconstruction of Destarched Wheat Bran by Enzymes Cocktail Used in Animal Nutrition

Wheat bran is a foodstuff containing more than 40% of non-starch polysaccharides (NSPs) that are hardly digestible by monogastric animals. Therefore, cocktails enriched of hydrolytic enzymes (termed NSPases) are commonly provided as feed additives in animal nutrition. However, how these enzymes cocktails contribute to NSPs deconstruction remains largely unknown. This question was addressed by employing an original methodology that makes use of a multi-instrumented bioreactor that allows to dynamically monitor enzymes in action and to extract in-situ physical and ex-situ biochemical data from this monitoring. We report here that the deconstruction of destarched wheat bran by an industrial enzymes cocktail termed Rovabio® was entailed by two concurrent events: a particles fragmentation that caused in <2 h a 70% drop of the suspension viscosity and a solubilization that released <30 % of the wheat bran NSPs. Upon longer exposure, the fragmentation of particles continued at a very slow rate without any further solubilization. Contrary to this cocktail, xylanase C alone caused a moderate 25% drop of viscosity and a very weak fragmentation. However, the amount of xylose and arabinose from solubilized sugars after 6 h treatment with this enzyme was similar to that obtained after 2 h with Rovabio®. Altogether, this multi-scale analysis supported the synergistic action of enzymes mixture to readily solubilize complex polysaccharides, and revealed that in spite of the richness and diversity of hydrolytic enzymes in the cocktail, the deconstruction of NSPs in wheat bran was largely incomplete.