Tzanko Tzanov

Decolorization and Detoxification of Textile Dyes with a Laccase from Trametes hirsuta

ABSTRACT Trametes hirsuta and a purified laccase from this organism were able to degrade triarylmethane, indigoid, azo, and anthraquinonic dyes. Initial decolorization velocities depended on the substituents on the phenolic rings of the dyes. Immobilization of theT. hirsuta laccase on alumina enhanced the thermal stabilities of the enzyme and its tolerance against some enzyme inhibitors, such as halides, copper chelators, and dyeing additives. The laccase lost 50% of its activity at 50 mM NaCl while the 50% inhibitory concentration (IC50) of the immobilized enzyme was 85 mM. Treatment of dyes with the immobilized laccase reduced their toxicities (based on the oxygen consumption rate of Pseudomonas putida) by up to 80% (anthraquinonic dyes). Textile effluents decolorized with T. hirsuta or the laccase were used for dyeing. Metabolites and/or enzyme protein strongly interacted with the dyeing process indicated by lower staining levels (K/S) values than obtained with a blank using water. However, when the effluents were decolorized with immobilized laccase, they could be used for dyeing and acceptable color differences (ΔE*) below 1.1 were measured for most dyes.

Bio-preparation of cotton fabrics

This study attempted to introduce the bio-processes in the conventional scouring and bleaching preparation of cotton. The scouring with two types of pectinases, acting under acidic and alkaline conditions respectively, was as efficient as the chemical process in terms of obtained adequate water absorbency of the fabrics. The necessity of surfactants application in scouring was outlined. Bleaching of the fabrics was performed with hydrogen peroxide, which was enzymatically produced by glucose oxidase during oxidation of glucose. The aeration plays an important role in the enhancement of the enzyme reaction, so that the quantity of generated peroxide is sufficient to overcome the stabilizing effect of the glucose and protein in the subsequent bleaching. A closed-loop process reusing starch containing desizing baths in a single step scouring/bleaching operation with enzyme-generated peroxide was performed.

Immobilization of catalases from Bacillus SF on alumina for the treatment of textile bleaching effluents

A catalase preparation from a newly isolated Bacillus sp. was covalently immobilized on silanized alumina using glutaraldehyde as crosslinking agent. The effect of the coupling time of the enzyme-support reaction was determined in terms of protein recovery and immobilization yield and a certain balance point was found after which the activity recovery decreased. The activity profile of the immobilized catalase at high pH and temperature was investigated. The immobilized enzyme showed higher stabilities (214 h at pH 11, 30 degrees C) at alkaline pH than the free enzyme (10 h at pH 11, 30 degrees C). The immobilized catalase was inhibited by anionic stabilizers or surfactants added to the hydrogen peroxide substrate solution.

Sonochemical Coating of Textiles with Hybrid ZnO/Chitosan Antimicrobial Nanoparticles

Textiles are good substrates for growth of microorganisms especially under moisture and temperature conditions found in hospitals. Microbial shedding from the body occurs continuously at contact of the patient with textile materials used in medical practices, contributing to the occurrence of hospital acquired infections. Thus, the use of efficient antimicrobial textiles is necessary to prevent the transfer of pathogens and the infection incidence. In this work, hybrid antimicrobial coatings were generated on cotton fabrics by means of a one-step simultaneous sonochemical deposition of ZnO nanoparticles (NPs) and chitosan. The process was further optimized in terms of reagents concentration and processing time in order to improve the antibacterial properties of the fabric and ensure their biocompatibility. The highest antibacterial activity of the fabrics against two medically relevant bacterial species was achieved in a 30 min sonochemical coating process using 2 mM ZnO NPs suspension. When chitosan was simultaneously deposited with the same amount of ZnO, the obtained hybrid NPs coating displayed higher by 48 and 17% antibacterial activity against Staphylococcus aureus and Escherichia coli, respectively. The presence of biopolymer also improved the durability of the antimicrobial effect of the coatings by 21% for Staphylococcus aureus and 40% for Escherichia coli, evaluated after applying multiple washing cycles at hospital laundering regimes. Finally, 87% biocompatibility improvement supported by fibroblast viability was observed for the hybrid ZnO/chitosan coating compared to the steady decrease of cells viability over one week in contact with the fabrics coated with ZnO alone.

Predicting dye biodegradation from redox potentials

Two biological approaches for decolorization of azo sulfonated dyes have been compared: reductive decolorization with the ascomycete yeast Issatchenkia occidentalis and enzymatic oxidative decolorization with Trametes villosa laccase alone or in the presence of the mediator 1‐hydroxybenzotriazole. The redox potential difference between the biological cofactor involved in the reductive activity of growing cells and the azo dye is a reliable indication for the decolorization ability of the biocatalyst. A linear relationship exists between the redox potential of the azo dyes and the decolorization efficiency of enzyme, enzyme/mediator, and yeast. The less positive the anodic peak of the dye, the more easily it is degraded oxidatevely with laccase. The more positive the cathodic peak of the dye, the more rapidly the dye molecule is reduced with yeast.

Studies of stabilization of native catalase using additives

Native catalase preparations isolated from Bacillus Sp were formulated with different additives for storage stabilization and better performance at high temperature and pH. The additives studied were: polyethylene glycol, glycerol, BSA, casein, glutaraldehyde, n-butylamine, ethylenediamine, 1.6-diaminohexane, BSA/glutaraldehyde and casein/glutaraldehyde. The glycerol and glutaraldehyde showed the best performance for long-term storage at 30°C and neutral pH. No stabilization additives were effective at pH 12, but below that pH the polyethylene glycol and glycerol appeared to be the most appropriate. Amines, polyethylene glycol and glycerol shifted the pH activity maximum of the native catalase toward more alkaline region, while glycerol were the only additive to improve the temperature profile of the enzyme.

Comparative study of the efficiency of synthetic and natural mediators in laccase-assisted bleaching of eucalyptus kraft pulp

The natural phenolic compounds syringaldehyde and vanillin were compared to the synthetic mediators 1-hydroxybenzotriazole, violuric acid and promazine in terms of boosting efficiency in a laccase-assisted biobleaching of eucalyptus kraft pulp. Violuric acid and 1-hydroxybenzotriazole revealed to be the most effective mediators of the bioprocess. Nevertheless, laccase-syringaldehyde system also improved the final pulp properties (28% delignification and 63.5% ISO brightness) compared to the process without mediator (23% and 61.5% respectively), in addition to insignificant denaturation effect over laccase. The efficiency of the biobleaching process was further related to changes in non-conventionally used optical and chromatic parameters of pulp, such as (L*), chroma (C*) and dye removal index (DRI) showing good correlation. Adverse coupling reactions of the natural phenolic mediators on pulp lignin were predicted by electrochemical studies, demonstrating the complexity of the laccase-mediator reaction on pulp.

Chitin, Chitosan and Derivatives for Wound Healing and Tissue Engineering

Naturally derived polymers possess a number of properties beneficial to wound healing and tissue engineering. The polysaccharides chitin and chitosan appear to be suitable candidates for the preparation of dressing materials and scaffolds for tissue regeneration due to their unique structural, physico-chemical and functional properties. Functionalization of these biopolymers for improvement of properties such as solubility or introduction of active functions and blending with other intrinsically bioactive polymers has attracted considerable attention in recent years. Such modifications would allow going beyond traditional approaches for treatments of dermal injuries. This chapter is a critical review of the advances in chitin and chitosan functionalization for wound-healing and tissue-engineering applications.

Thermo-alkali-stable catalases from newly isolated Bacillus sp. for the treatment and recycling of textile bleaching effluents

Three thermoalkaliphilic bacteria, which were grown at pH 9.3-10 and 60-65 degrees C were isolated out of a textile wastewater drain. The unknown micro-organisms were identified as thermoalkaliphilic Bacillus sp. Growth conditions were studied and catalase activities and stabilities compared. Catalases from Bacillus SF showed high stabilities at 60 degrees C and pH 9 (t1/2=38 h) and thus this strain was chosen for further investigations, such as electron microscopy, immobilization of catalase and hydrogen peroxide degradation studies. Degradation of hydrogen peroxide with an immobilized catalase from Bacillus SF enabled the reuse of the water for the dyeing process. In contrast, application of the free enzyme for treatment of bleaching effluents, caused interaction between the denaturated protein and the dye, resulting in reduced dye uptake, and a higher color difference of 1.3DeltaE* of dyed fabrics compared to 0.9DeltaE* when using the immobilized enzyme.

Multifunctional modification of wool using an enzymatic process in aqueous–organic media

An enzymatic method using laccases for grafting the water insoluble phenolic compound lauryl gallate on wool fabric was developed. To find the compromise conditions at which the substrate is soluble while the enzyme remains active, the reaction was carried out in an 80/20 (v/v, %) aqueous-ethanol mixture, where the enzyme retains 75-80% of its activity. The enzymatic coating of wool with lauryl gallate provided in a one-step process a multifunctional textile material with antioxidant, antibacterial and water repellent properties.