A Review of the Role of Amphiphiles in Biomass to Ethanol Conversion

Combined cross-linked enzyme aggregates of cyclodextrin glucanotransferase and maltogenic amylase from Bacillus lehensis G1 for maltooligosaccharides synthesis

Maltooligosaccharides (MOS) are functional oligosaccharides that can be synthesized through enzymatic cascade reaction between cyclodextrin glucanotransferase (CGTase) and maltogenic amylase (Mag1) from Bacillus lehensis G1. To address the problems of low operational stability and non-reusability of free enzymes, both enzymes were co-immobilized as combined cross-linked enzyme aggregates (Combi-CLEAs-CM) with incorporation of bovine serum albumin (BSA) and Tween 80 (Combi-CLEAs-CM-add). Combi-CLEAs-CM and Combi-CLEAs-CM-add showed activity recoveries of 54.12 % and 69.44 %, respectively after optimization. Combi-CLEAs-CM-add showed higher thermal stability at higher temperatures (40 °C) with longer half-life (46.20 min) as compared to those of free enzymes (36.67 min) and Combi-CLEAs-CM (41.51 min). Both combi-CLEAs also exhibited higher pH stability over pH 5 to pH 9, and displayed excellent reusability with >50 % of initial activity retained after four cycles. The reduction in K_m value of about 22.80 % and 1.76-fold increase in starch hydrolysis in comparison to Combi-CLEAs-CM attested the improvement of enzyme-substrate interaction by Tween 80 and pores formation by BSA in Combi-CLEAs-CM-add. The improved product specificity of Combi-CLEAs-CM-add also produced the highest yield of MOS (492 mg/g) after 3 h. Therefore, Combi-CLEAs-CM-add with ease of preparation, excellent reusability and high operational stability is believed to be highly efficacious biocatalyst for MOS production.

Interaction of enzymes with lignocellulosic materials: causes, mechanism and influencing factors

For the production of biofuel (bioethanol), enzymatic adsorption onto a lignocellulosic biomass surface is a prior condition for the enzymatic hydrolysis process to occur. Lignocellulosic substances are mainly composed of cellulose, hemicellulose and lignin. The polysaccharide matrix (cellulose and hemicellulose) is capable of producing bioethanol. Therefore, lignin is removed or its concentration is reduced from the adsorption substrates by pretreatments. Selected enzymes are used for the production of reducing sugars from cellulosic materials, which in turn are converted to bioethanol. Adsorption of enzymes onto the substrate surface is a complicated process. A large number of research have been performed on the adsorption process, but little has been done to understand the mechanism of adsorption process. This article reviews the mechanisms of adsorption of enzymes onto the biomass surfaces. A conceptual adsorption mechanism is presented which will fill the gaps in literature and help researchers and industry to use adsorption more efficiently. The process of enzymatic adsorption starts with the reciprocal interplay of enzymes and substrates and ends with the establishment of molecular and cellular binding. The kinetics of an enzymatic reaction is almost the same as that of a characteristic chemical catalytic reaction. The influencing factors discussed in detail are: surface characteristics of the participating materials, the environmental factors, such as the associated flow conditions, temperature, concentration, etc. Pretreatment of lignocellulosic materials and optimum range of shear force and temperature for getting better results of adsorption are recommended.

Electrochemical Conversion of the Lignin Model Veratryl Alcohol to Veratryl Aldehyde Using Manganese(III)-Schiff Base Homogeneous Catalysts

Lignin and other colored structures need to be bleached after the Kraft process in the pulp industry. Development of environmentally-safe bleaching catalysts or electrocatalysts constitutes an attractive strategy for selective removal of lignin. Seven manganese(III)-complexes with Schiff base ligands 1–7 were synthetized and characterized by different analytical and spectroscopic techniques. The tetragonally elongated octahedral geometry for the manganese coordination sphere and the global µ-aquo dimeric structure were revealed by X-ray diffraction (XRD) studies for 1, Mn2L12(H2O)2(N(CN)2)2 (N(CN)2 = dicyanamide). Complexes 1–4 behave as more efficient peroxidase mimics as compared to 5–7. Electrochemical oxidation of the lignin model veratrylalcohol (VA) to veratrylaldehyde (VAH) is efficiently catalyzed by a type of dimanganese(III) complexes in a chlorine-free medium. The electrocatalytic reaction proceeds through the oxidation of chloride into hypochlorite at alkaline pH along with the formation of hydrogen from water as a subproduct.

Evaluation of the action of Tween 20 non-ionic surfactant during enzymatic hydrolysis of lignocellulose: Pretreatment, hydrolysis conditions and lignin structure

The aim of this work was to study the effects of pretreatment process, hydrolysis condition and structural features of lignin on the improving action of surfactants (Tween 20) for enzymatic hydrolysis of pretreated wheat straw, and further to interpret the relation of these factors with the non-productive adsorption of cellulases on lignin. Tween 20 seemed to be more greatly improve cellulose conversion under harsher conditions. The surfactant showed more significant improvement for acid-pretreated substrates than oxidative-pretreated substrates. Highly-condensed lignin and phenolic hydroxyl groups showed much stronger adsorption ability to cellulases, while Tween 20 could well block the lignin-cellulase interactions recovering cellulose hydrolyzability. It was proposed that pretreatments altered lignin structures, resulting in the change of surface properties thus further impacting the lignin-cellulase interactions. Addition of Tween 20 could modify lignin surface properties to change its hydrophobicity, hydrogen bonding ability and surface charges, thus reducing the non-productive adsorption of proteins.

An effective surfactant-assisted hydrothermal pretreatment strategy for bioethanol production from chili post-harvest residue by separate hydrolysis and fermentation

Surfactants play major role in the delignification of lignocellulosic biomass. Surfactant-assisted hydrothermal pretreatment was evaluated for chili post-harvest residue. Maximum reducing sugar yield of 0.445 g per g of dry biomass (g/g) was obtained when surfactant PEG 6000 was used. Compositional analysis revealed an efficient removal of lignin and hemicelluloses from the pretreated biomass. Fermentation inhibitors such as furfural, 5-hydroxymethylfurfural and organic acids were absent in the hydrolyzate. After pretreatment, the biomass can be directly hydrolyzed without any neutralization, washing and drying, and the hydrolyzate is devoid of major fermentation inhibitors. Fermentation with Saccharomyces cerevisiae yielded 1.84% of ethanol with a fermentation efficiency of 63.88%.