Cross-Linked Enzyme Aggregates and Their Application in Enzymatic Pretreatment of Microalgae: Comparison Between CLEAs and Combi-CLEAs

Carrier-free immobilization is a key process to develop efficient biocatalysts able to catalyze the cell wall degradation in microalgae where the traditional solid supports cannot penetrate. Thus, the insolubilization of commercial Celluclast®, Alcalase®, and Viscozyme® enzymes by carrier-free immobilization and their application in microalgae pretreatment was investigated. In this study, different precipitants at different ratios (ethanol, acetone, and polyethylene glycol 4000) were tested in the first part of the method, to establish the precipitation conditions. The screening of the best precipitant is needed as it depends on the nature of the enzyme. The best results were studied in terms of immobilization yield, thermal stability, and residual activity and were analyzed using scanning electron microscopy. Moreover, a novel strategy was intended including the three enzymes (combi-CLEAs) to catalyze the enzymatic degradation of Nannochloropsis gaditana microalgal cell wall in one pot. The carrier-free immobilized derivatives were 10 times more stable compared to soluble enzymes under the same. At the best conditions showed its usefulness in the pretreatment of microalgae combined with ultrasounds, facilitating the cell disruption and lipid recovery. The results obtained suggested the powerful application of these robust biocatalysts with great catalytic properties on novel and sustainable biomass such as microalgae to achieve cost-effective and green process to extract valuable bioactive compounds.

Enzymatic and Microwave Pretreatments and Supercritical CO2 Extraction for Improving Extraction Efficiency and Quality of Origanum vulgare L. spp. hirtum Extracts

The goal of the study was to establish a procedure for improving the efficiency of supercritical carbon dioxide (scCO₂) extraction of Origanum vulgare L. spp. hirtum (Greek oregano) and enhancing the quality of obtained extracts. Microwave and enzymatic pretreatments of the plant material were applied prior to the scCO₂ extraction. It was determined that the microwave pretreatment with irradiation power 360 W during 2 min accelerated the extraction of lipophilic compounds and provided a twofold higher extraction yield compared to the control. Moreover, this pretreatment also led to an increase in oxygenated monoterpenes content and the most dominant component carvacrol, as well as the extracts' antioxidant activity. The enzymatic pretreatment caused a significant increase in the extraction yield and the attainment of the extract with the most potent antioxidant properties. Coupling the pretreatments with scCO₂ extraction improves the process of obtaining high value lipophilic products of oregano in terms of utilization of the plant material, acceleration of the extraction with the possibility to adjust its selectivity and quality of extracts, and enhancement of biological activity.

Application crude multienzyme extract from Aspergillus niger as a pretreatment for the extraction of essential oil from Croton argyrophyllus leaves

Leaves of Croton argyrophyllus contain essential oil with promising active components for the development of drugs and botanical insecticides. In this study, we evaluated the enzymatic pretreatment process to increase the extraction of essential oil from fresh and dried leaves of C. argyrophyllus. Pretreatment was carried out using a crude multienzymatic extract obtained via solid-state fermentation of forage palm by Aspergillus niger, and the extraction was performed by hydrodistillation. A Doehlert matrix was used to optimize the enzymatic pretreatment variables temperature and enzymatic extract. The effect of pretreatment time was also investigated. At optimum experimental conditions, 41.34°C, 140 min, and 130.73 mL of enzyme in 369.27 mL of water, the essential oil yield from fresh leaves subjected to enzymatic pretreatment increased by 9.35% and that from dry leaves by 6.77%. Based on chromatographic analysis (GC-MS), no compound was degraded in the extraction process. Micromorphological analysis confirmed the rupture of the glandular trichomes, favoring essential oil release. Therefore, enzymatic pretreatment associated with hydrodistillation increased the essential oil yield and is a promising application to obtain essential oil for therapeutic purposes without altering its composition.

Enzymatic Pretreatment with Laccases from Lentinus sajor-caju Induces Structural Modification in Lignin and Enhances the Digestibility of Tropical Forage Grass (Panicum maximum) Grown under Future Climate Conditions

Since laccase acts specifically in lignin, the major contributor to biomass recalcitrance, this biocatalyst represents an important alternative to the pretreatment of lignocellulosic biomass. Therefore, this study investigates the laccase pretreatment and climate change effects on the hydrolytic performance of Panicum maximum. Through a Trop-T-FACE system, P. maximum grew under current (Control (C)) and future climate conditions: elevated temperature (2 °C more than the ambient canopy temperature) combined with elevated atmospheric CO₂ concentration(600 μmol mol⁻¹), name as eT+eC. Pretreatment using a laccase-rich crude extract from Lentinus sajor caju was optimized through statistical strategies, resulting in an increase in the sugar yield of P. maximum biomass (up to 57%) comparing to non-treated biomass and enabling hydrolysis at higher solid loading, achieving up to 26 g L⁻¹. These increments are related to lignin removal (up to 46%) and lignin hydrophilization catalyzed by laccase. Results from SEM, CLSM, FTIR, and GC-MS supported the laccase-catalyzed lignin removal. Moreover, laccase mitigates climate effects, and no significant differences in hydrolytic potential were found between C and eT+eC groups. This study shows that crude laccase pretreatment is a potential and sustainable method for biorefinery solutions and helped establish P. maximum as a promising energy crop.

Combination of Synergic Enzymes and Ultrasounds as an Effective Pretreatment Process to Break Microalgal Cell Wall and Enhance Algal Oil Extraction

Microalgal biomass is a sustainable source of bioactive lipids with omega-3 fatty acids. The efficient extraction of neutral and polar lipids from microalgae requires alternative extraction methods, frequently combined with biomass pretreatment. In this work, a combined ultrasound and enzymatic process using commercial enzymes Viscozyme, Celluclast, and Alcalase was optimized as a pretreatment method for Nannochloropsis gaditana, where the Folch method was used for lipid extraction. Significant differences were observed among the used enzymatic pretreatments, combined with ultrasound bath or probe-type sonication. To further optimize this method, ranges of temperatures (35, 45, and 55 °C) and pH (4, 5, and 8) were tested, and enzymes were combined at the best conditions. Subsequently, simultaneous use of three hydrolytic enzymes rendered oil yields of nearly 29%, showing a synergic effect. To compare enzymatic pretreatments, neutral and polar lipids distribution of Nannochloropsis was determined by HPLC-ELSD. The highest polar lipids content was achieved employing ultrasound-assisted enzymatic pretreatment (55 °C and 6 h), whereas the highest glycolipid (44.54%) and PE (2.91%) contents were achieved using Viscozyme versus other enzymes. The method was applied to other microalgae showing the potential of the optimized process as a practical alternative to produce valuable lipids for nutraceutical applications.

A novel pretreatment biotechnology for increasing methane yield from lipid-rich wastewater based on combination of hydrolytic enzymes with Candida rugosa fungus

Lipid-rich wastewater from the local dairy industry (cheese whey) in the Galilee, Israel was hydrolyzed by using two different sources of lipase as hydrolytic enzymes: fungal (Candida rogusa lipase-AY) and animal porcine pancreatic lipase(PPL). Pretreatment efficiency was verified by comparative biodegradability tests of raw and treated wastewater samples. Simultaneous hydrolysis and anaerobic digestion in the same reactors were also tested. Enzymatic pretreatment of these samples at a concentration of 0.05 w v^-1 showed organic matter removal of 90% and methane formation increases of 140% for the fungal source enzyme (i.e., AY), while for the animal source enzyme (i.e., PPL) was 86 and 130%, respectively. Enzymatic pretreatment led to significant methane formation which was obtained only for moderate substrate concentration (initial chemical oxygen demand of 15 gL^-1); While in high concentrated lipid-rich wastewater led to methane yield inhibition. The main finding was that the combination of AY enzyme with Candida rugosa fungus (i.e., enzyme mixture) led to a high efficiency in methane production (+152%) and organic materials removal (more than 90%). In summary, the use of fungal hydrolytic lipase mixed with Candida rugosa fungus is a promising method for enhancing methane production during the biodegradation of fat and grease-rich wastewaters.

Potential of Xylanases to Reduce the Viscosity of Micro/Nanofibrillated Bleached Kraft Pulp

The generally high viscosity of micro/nanofibrillated cellulose limits its applications in cream and fluid products. A bleached softwood Kraft (BSK) pulp was refined with increasing energy (500-2500 kWh t^-1) to produce micro/nanofibrillated cellulose (MNBSK). Subsequent xylanase treatment was shown to influence the viscosity, gel point, aspect ratio, and fiber surface morphology of the MNBSK. It was apparent that the accessibility to xylanases was increased even at low refining energies (500 kWh t^-1). Depending on the initial degree of cellulose fibrillation, xylanase treatment decreased the viscosity of the MNBSK from 4190-2030 to 681-243 Pa·s at a shear rate of 0.01 s^-1, corresponding to the reduction in the aspect ratio from 183-296 to 163-194. It was likely that the xylanases were predominantly acting on the xylan present on the fiber surfaces, reducing the cross-linking points on the cellulose fibers and consequently resulting in the reduction in MNBSK viscosity.

Assessing the Effect of Pretreatments on the Structure and Functionality of Microbial Communities for the Bioconversion of Microalgae to Biogas

Microalgae biomethanization is driven by anaerobic sludge associated microorganisms and is generally limited by the incomplete hydrolysis of the microalgae cell wall, which results in a low availability of microalgal biomass for the methanogenic community. The application of enzymatic pretreatments, e.g., with hydrolytic enzymes, is among the strategies used to work around the incomplete hydrolysis of the microalgae cell wall. Despite the proven efficacy of these pretreatments in increasing biomethanization, the changes that a given pretreatment may cause to the anaerobic sludge associated microorganisms during biomethanization are still unknown. This study evaluated the changes in the expression of the metatranscriptome of anaerobic sludge associated microorganisms during Chlorella sorokiniana biomethanization without pretreatment (WP) (control) and pretreated with commercial cellulase in order to increase the solubilization of the microalgal organic matter. Pretreated microalgal biomass experienced significant increases in biogas the production. The metatranscriptomic analysis of control samples showed functionally active microalgae cells, a bacterial community dominated by γ- and δ-proteobacteria, and a methanogenic community dominated by Methanospirillum hungatei. In contrast, pretreated samples were characterized by the absence of active microalgae cells and a bacteria population dominated by species of the Clostridia class. These differences are also related to the differential activation of metabolic pathways e.g., those associated with the degradation of organic matter during its biomethanization.

Effect of High-Pressure Processing on Human Noroviruses in Laboratory-Contaminated Oysters by Bio-Accumulation

The contamination of oysters with human noroviruses poses a human health risk, since oysters are often consumed raw. In this study, human norovirus genogroup II was allowed to bio-accumulate in oysters, and then the effect of high-pressure processing (HPP) on human noroviruses in oysters was determined through a polymerase chain reaction (PCR)-based method with enzymatic pretreatment to distinguish infectious noroviruses. As a result, oysters could be artificially contaminated to a detectable level of norovirus genome by the reverse transcription-PCR. Concentrations of norovirus genome in laboratory-contaminated oysters were log normally distributed, as determined by the real-time PCR, suggesting that artificial contamination by bio-accumulation was successful. In two independent HPP trials, a 1.87 log₁₀ and 1.99 log₁₀ reduction of norovirus GII.17 genome concentration was observed after HPP at 400 MPa for 5 min at 25°C. These data suggest that HPP is a promising process of inactivation of infectious human noroviruses in oysters. To our knowledge, this is the first report to investigate the effect of HPP on laboratory-contaminated noroviruses in oysters.

Performance of a Two-Stage Membrane System for Bromelain Separation from Pineapple Waste Mixture as Impacted by Enzymatic Pretreatment and Diafiltration

Membrane technology has been successfully applied for the purification of bromelain, a protease enzyme from pineapple. However, the current system operates less optimally in terms of flux and separation primarily due to properties of the feed, such as viscosity. Hence, in this study, enzymatic pretreatment and diafiltration operation were employed in a two-stage ultrafiltration (UF) system to enhance the performance of the purification and concentration process of bromelain enzyme from an extract of pineapple crude waste mixture (CWM). Pretreatment of the CWM extract using either pectinase or cellulase, or the combination of both, was applied and compared regarding the apparent viscosity reduction. Diafiltration step was introduced in UF stage 2 and observations on the flux performance, enzyme recovery and enzyme purity were made. A 12% apparent viscosity reduction was achieved when the CWM extract was pretreated with pectinase which led to 37-38% improvement in the flux performance of both UF stages, as well as higher enzyme recovery in UF stage 1. The introduction of diafiltration mode in UF stage 2 managed to sustain high flux values while yielding 4.4-fold enzyme purity (higher than a 2.5-fold purity achieved in our previous work); however, high diluent consumption was needed. The outcomes of this study showed that the flux performance and bromelain separation can be enhanced by reducing the viscosity with the employment of enzymatic pretreatment and diafiltration operation. Thus, both techniques can be potentially applied in a large-scale membrane-based process for bromelain production.

Co-cultivation of Aspergillus nidulans Recombinant Strains Produces an Enzymatic Cocktail as Alternative to Alkaline Sugarcane Bagasse Pretreatment

Plant materials represent a strategic energy source because they can give rise to sustainable biofuels through the fermentation of their carbohydrates. A clear example of a plant-derived biofuel resource is the sugar cane bagasse exhibiting 60-80% of fermentable sugars in its composition. However, the current methods of plant bioconversion employ severe and harmful chemical/physical pretreatments raising biofuel cost production and environmental degradation. Replacing these methods with co-cultivated enzymatic cocktails is an alternative. Here we propose a pretreatment for sugarcane bagasse using a multi-enzymatic cocktail from the co-cultivation of four Aspergillus nidulans recombinant strains. The co-cultivation resulted in the simultaneous production of GH51 arabinofuranosidase (AbfA), GH11 endo-1,4-xylanase (XlnA), GH43 endo-1,5-arabinanase (AbnA) and GH12 xyloglucan specific endo-β-1,4-glucanase (XegA). This core set of recombinant enzymes was more efficient than the alternative alkaline method in maintaining the cellulose integrity and exposing this cellulose to the following saccharification process. Thermogravimetric and differential thermal analysis revealed residual byproducts on the alkali pretreated biomass, which were not found in the enzymatic pretreatment. Therefore, the enzymatic pretreatment was residue-free and seemed to be more efficient than the applied alkaline method, which makes it suitable for bioethanol production.