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Special review paper: Enzymes in the leather industry
Abstract
The leather industry has been facing new challenges including the need to improve and optimize processes to achieve the required quality in their final articles and meet the requirements of environmental legislation. The enzymatic treatment of leather is a promising technology. Enzymes are organic substances, generally proteins, known as biocatalysts for multiplex che mical reactions. They have been explored commercially in the detergent, food, pharmaceutical, diagnostic, fine chemical and other industries. Commonly, the most promising enzyme sources are microorganisms. Several studies have reported enzyme use in different stages of leather production, describing a decrease in the use of chemicals for the depilation and liming steps, and some have also reported the complete replacement of chemicals with enzymes. Some authors use enzymes to increase the exhaustion of dyes in dye baths and to increase the effectiveness of tanning in the tanning step. The identification of a new enzyme is a long process, requiring screening for specific criteria, isolation and selection of new bacteria, and the investigation of the nutrients and conditions necessary for growth and enzyme production by the selected microorganism. Finally, issues such as pH, temperature and product inhibition of the enzyme during its application in the processing of skins/hides should be studied.
- ... The results confirmed that the enzymatic dehaired leathers exhibited comparable leather qualities with an eco-friendly approach to cleaner leather (Kandasamy et al., 2012). By using this method it is possible to produce eco-friendly leather and also to replace sulphide completely by this process (Arunachalam and Saritha, 2009;Verma et al., 2011;Dettmer et al., 2013;Subbarao et al., 2009). Alkaline protease (George et al., 2014) obtained from vibrio metschnikovii NG155, at pH 10, temperature 65 C effectively dehairs the skins. ...... In addition to that better physiochemical properties of dyed crust and lesser pollution load in dehairing process were achieved in leather processing. Dettmer et al. (2013Dettmer et al. ( , 2012 reviewed use of enzymes in leather processing to improve and optimize process and to produce good quality of leather. Combination of 4% hydrogen peroxide with enzyme at the level of 100e300 U g/l is a viable method of unhairing process to replace lime and sulphide from the conventional process for the production of better quality leather. ...The leather industry deals with proteinous skin material for the conversion of leather and this generates huge amount of solid and liquid wastes giving rise to pollution that needs to be overcome by introducing sustainable cleaner technologies. This review describes various eco-friendly challenges and major achievements for abatement of pollution in leather processing. Different cleaner technological methods in preservation of raw hides/skins, unhairing, tanning and dyeing operations are discussed here. Cleaner-preservation techniques by using chemicals and biological agents have been developed to reduce pollution problems of salt up to a great extent in leather processing operations. Process intensified operations have helped to achieve better uptake and to manage pollution load. Enzymatic dehairing are implemented to reduce Bio-chemical-Oxygen-Demand (BOD) at the level of 40%, Chemical-Oxygen-Demand (COD) up to 50%. Improved biological methods for bio-degradation of dyes, azo-dyes and their mixtures and to reuse the liquors in the process to reduce the dye pollution load in the effluent streams are reviewed. Nano-Particle polymers and improved retanning materials have been synthesized for high exhaustion of dyeing and retanning properties. Mathematical models predicting kinetics and growth for the above processes are also reviewed. It could be concluded by utilization of these technologies, a possible reduction in pollution loads such as BOD & COD, upto levels of 50% & 40%, could be achieved in leather processing.
- ... The results confirmed that the enzymatic dehaired leathers exhibited comparable leather qualities with an eco-friendly approach to cleaner leather ( Kandasamy et al., 2012). By using this method it is possible to produce eco-friendly leather and also to replace sulphide completely by this process (Arunachalam and Saritha, 2009;Verma et al., 2011;Dettmer et al., 2013;Subbarao et al., 2009). Alkaline protease (George et al., 2014) obtained from vibrio metschnikovii NG155, at pH 10, temperature 65 C effectively dehairs the skins. ...... In addition to that better physiochemical properties of dyed crust and lesser pollution load in dehairing process were achieved in leather processing. Dettmer et al. (2013Dettmer et al. ( , 2012) reviewed use of enzymes in leather processing to improve and optimize process and to produce good quality of leather. Combination of 4% hydrogen peroxide with enzyme at the level of 100e300 U g/l is a viable method of unhairing process to replace lime and sulphide from the conventional process for the production of better quality leather. ...
- ... Thermophilic prokaryotes express thermostable enzymes that are used as biocatalysts in pharmaceutical, food processing and several other industries (Baltaci et al., 2017;Mohammed et al., 2017). In addition to thermal stability, the enzymes are also stable against detergents, organic solvents, high acidity and alkalinity, hence their use in various industries (Bhalla et al., 2013;Dettmer et al., 2013). ...The most prevalent Mycobactrium species in the Mycobaterium tuberculosis complex and frequency of mutations in the genes conferring resistance to rifampicin and isoniazid in Zambia have until now remained unkown. This study sought to diferrentiate the isolates of Mycobaterium tuberculosis complex (MTBC) using genetic regions cfp32, RD9 and RD12 and determine the prevalence of resistance-associated mutations in two specific resistance marker genes (rpoB and katG) and the inhA promoter region of M. tuberculosis isolated at the University Teaching Hospital Tuberculosis Laboratory (Lusaka, Zambia) between January 2013 and June 2014. Genomic DNA was extracted from 40 isolates and amplified by multiplex PCR fro regions cfp32, RD9 and RD12 and single PCRs for three drug-resistance conferring loci (rpoB, katG and inhA). All isolates were positive for the three regions typical of M. tuberculosis. Seventy-five percent had S315T mutations in katG gene and one had mutations in the inhA promoter and rpoB in addition to the katG 315 mutation. The S450L (48.7%) and H445y (20.5%) mutations were the most frequently observed mutations in the rpoB gene while rifampicin mono-resistance was observed in 2.6% of the rifampicin-resistant isolates. Molecular diagnosis tests basdd on detecting these predominant mutations could be useful for the rapid detection of multidrug resistant tuberculosis in Eastern, Lusaka, western parts of Zambia and TB patients in these regions can be treated with the standard first line tuberculosis drugs.
- ... It is a highly stable and more flexible protein cross-linked by its lysine residues (Kagan et al. 1972). Although it is resistant to alkali and acid degradation as well as proteolytic degradation, it can be degraded by certain proteases with elastinolytic activities, and proteases have been widely used in various process stages, such as soaking, unhairing, and bating in the leather manufacturing process (Taylor et al. 1987;Pal et al. 1996;Choudhary et al. 2004;Dettmer et al. 2013). The final leather quality is significantly affected by the elastin degradation, which improves the final leather properties such as softness, area yield, and flatness (Ornes et al. 1960;Alexander 1988). ...Leather biotechnology based on enzyme is one of the main directions toward clean technology in the leather manufacturing process. Proteins such as collagen, elastin, and keratin are important components in animal hides or skins, and proteases are most frequently used in the leather manufacturing process for the removal of interfibrillar substance and opening-up of collagen fiber instead of toxic chemicals. Elastin is an important and highly elastic structural protein in the animal hides or skins and significantly affects the properties of the final leather product. For improving the quality of leather product, thorough understanding of the mechanism of action of proteases on elastin is necessary. The action of proteases on elastin has been mostly studied either qualitatively by histological analysis or quantitatively based on substrate casein or stained substrates, such as congo red-elastin and Remazol Brilliant Blue R-elastin; however, the resulting products have not been accurately characterized and thus these methods are not up to the standard. Besides, controlling the hydrolytic action of proteases to elastin has been very difficult, and excessive hydrolytic action of protease damages the elastin, restricting the wide application of proteases in the leather manufacturing process. In order to quantitatively evaluate the hydrolytic action of proteases on elastin in a more accurate manner, in this study, a new method was established by determining the unique amino acid desmosine based on the covalently bonded elastin–desmosine conjugate. Quantitative analysis of desmosine was performed in liquor based on cowhides substrate, and qualitative characterization was accomplished by histological analysis of elastic fiber in hides using an optical microscope. The results of this study indicated that the newly developed method is sensitive, accurate, and reproducible. In addition, the unhairing trials also demonstrated the suitability of newly established method in the leather manufacturing process to evaluate the action of proteases on the elastin in animal hides or skins.
- ... Thermophilic microorganisms (optimum growth temperature of 50 ∘ C or above) have attracted great attention among extremophiles because they are sources of thermostable enzymes (such as amylases, cellulases, chitinases, pectinases, xylanases, proteases, lipase, and DNA polymerases); these enzymes show unique features that can be suitable for performing biotechnological processes at elevated temperatures [8]. Moreover, they have been reported to be more stable 2 International Journal of Microbiology against many solvents, detergents, and acidic and alkaline pH [9,10]. Among these commercially important enzymes are the protease enzymes: alkaline protease possesses the property of a great stability when used in detergents and protease enzymes have found applications in bioindustries such as washing powders, food industry, leather processing, and pharmaceuticals and for studies in biology [11,12]. ...The aim of this study was the isolation and characterization of thermophilic bacteria from hot springs in Jordan. Ten isolates were characterized by morphological, microscopic, biochemical, molecular, and physiological characteristics. Sequencing of the 16S rDNA of the isolates followed by BLAST search revealed that nine strains could be identified as Bacillus licheniformis and one isolate as Thermomonas hydrothermalis . This is the first report on the isolation of Thermomonas species from Jordanian hot springs. The isolates showed an ability to produce some thermostable enzymes such as amylase, protease, cellulose, gelatins, and lecithin. Moreover, the UPGMA dendrogram of the enzymatic characteristics of the ten isolates was constructed; results indicated a high phenotypic diversity, which encourages future studies to explore further industrial and environmental applications.
- ... O composto orgânico à base de pelo vacum tem um possível mercado nas granjas, viveiros, jardins e cultivos orgânicos, com certas vantagens em relação a outros fertilizantes, por sua liberação mais lenta de nitrogênio (Careri e Morra, 2010). A aplicação de enzimas (Dettmer et al., 2013a) na etapa de depilação de peles bovinas (processo hair saving), vem sendo estudada com o objetivo de se obter pelos intactos ao final do processo. Entre as pesquisas realizadas estão a depilação co-enzimática (Souza et al., 2012), a depilação enzimática (Dettmer et al., 2013b), e a depilação enzimática-oxidativa (Andrioli e Gutterres, 2014). ...
- ... With increasing concerns of environmental protection, hair-saving unhairing technique, to a greater extent, is used in tanneries, which can eliminate dissolution of hair and remarkably alleviate impact of wastewater pollution. [13][14][15][16] However, a large amount of hair, as solid waste, is generated. 17 Therefore, more research has been focused on the recycling of tannery hair. ...In consideration of the fact that the hydrolysate of hair contains antioxidant and free radical scavenging groups, the inhibitory effect of protein filling agent prepared from bovine hair (HPFA) on the oxidation of Cr(III) was investigated. The results demonstrated that HPFA possessed remarkable reducing ability to transfer Cr(VI) to Cr(III) in solution when pH was lower than 6.0. The reduction reaction was enhanced with rise of temperature, extension of reaction time and increase of HPFA dosage. Meanwhile, the HPFA also presented a high activity to inhibit the oxidation of Cr(III) in chrome liquor in the presence of unsaturated fish oil fatliquor. More interestingly, the HPFA achieved satisfactory inhibitory effect on Cr(III) oxidation in leather in the temperature range from 20 degrees C to 100 degrees C. Its inhibitory activity was much higher than that of commercial protein filling agent made from collagen hydrolysate. All the results suggested that bovine hair could be used as a potential resource for preparing protein filling agent with both filling and Cr(III) oxidation inhibiting properties.
- ... In addition to that better physiochemical properties of dyed crust and lesser pollution load in dehairing process were achieved in leather processing. Dettmer et al. (2012Dettmer et al. ( , 2013) reviewed use of enzymes in leather processing to improve and optimize process and to produce good quality of leather. But, the limitation of the enzymatic method is that the maintenance and dependence of the process on different parameters like, pH, temperature and activity of enzyme. ...The dehairing of goat skin using sodium percarbonate has been attempted in place of conventional dehairing using lime and sodium sulfide. Conventional dehairing generates huge pollution loads to the maximum level in leather processing. The present method is very simple that dehairs the goat skin with the help of 5% sodium percarbonate at an optimum level in combination with 4% sodium hydroxide and replaces hazardous material like sodium sulfide. The complete dehairing was achieved in 16 h duration. The pollution loads in terms of BOD, COD, Total Dissolved Solids (TDS), and Total Suspended Solids (TSS) were reduced up to the level of 56.3, 62.5, 68.1, and 52% in comparison with the control sample. Reduction of TOC values has been noticed. The advantage of the method lies with the fact that the processing time for leather making is considerably reduced by skipping reliming and deliming unit processes. A mechanistic mathematical model describing the diffusion reaction phenomena of dehairing agent through pores of skin has been developed that supports monolayer adsorption by Langmuir isotherm. Thermo gravimetric analysis and differential scanning calorimetry results explain that the present unit operation is dominated by exothermic process. Experimental samples show improved uptake of color with comparable leather qualities.
- ... These enzymes have been reported to be more stable against many solvents, detergents, acidic and alkaline pH, and high temperatures. Because of these properties, the isolation and identification of thermophilic bacteria, and the determination and characterization of the enzymes from these bacteria are very essential (Bhalla et al. 2013;Dettmer et al. 2013). ...In this study, the isolation, identification and characterization of the thermophilic bacteria from different hot springs in Turkey were carried out by conventional (morphological, physiological and biochemical tests) and molecular methods (FAMEs, GTG5-PCR and 16S rRNA sequencing). In addition, these thermophilic bacteria were tested for enzyme production capacities such as lipase, protease, amylase and cellulase. Anoxybacillus kaynarcensis (O20) could be a novel species according to identification studies, and all of the isolates showed the capacities to produce industrially valuable enzymes while screening for enzyme potentials; moreover, most of them could produce at least two of these enzymes.
- The leather industry earns special attention because of its strong potential for foreign exchange earnings and employment generation prospects. This industry has developed enormously over the past decades; since, leather has become a material of choice in the world of fashion. However, this industry, like many others, is facing stringent environmental regulations worldwide, due to vast usage of toxic chemicals and generation of hazardous waste. Leather manufacturing involves conversion of raw skins and hides into leather through a series of mechanical and chemical operations. Processes like pre-tanning and tanning are known to contribute ~ 80–90% of the total pollution load in tanneries. In order to mitigate the hazards caused by toxic chemicals, enzymes have been identified as a practical alternative for use during processing and as well as for waste management. Even though the use of enzymes in the leather industry dates long back mainly because of their activity on proteins and fat, the complete replacement of chemicals by enzymes has yet to be realized. Earlier, enzymes were derived from animal excreta, and later on from the pancreas of cattle. However, currently, the enzymes are almost entirely produced by microbial fermentation. In light of this, the current review presents a holistic view on the effective utilization of enzymes in leather making, mainly during soaking, dehairing, bating and degreasing processes in order to minimize waste generation, and also in the recovery of valuable and saleable by-products. Globally, ~ 7 million tons of salted bovine hides are used every year for leather making. By using enzymes in bio-preparation, around 8 million gigajoules of energy saving and 0.7 million tons of CO2 savings is estimated to be achieved due to lower processing times and associated energy use. Nevertheless, the search for enzymes for their ultimate application in the leather industry as an eco-friendly alternative continues, since, this process is far safer and more pleasant than the traditional method. The progress made in this field during the past two decades are highlighted and will provide further insight on the scope for utilization of enzymes in this industry. In order to achieve sustainability, clean environment and prevent health hazards, the leather industry ought to adopt the use of eco-friendly alternatives which might primarily depend on research, development and implementation of the potential enzyme technology.
- The present study investigated the potential of thermophilic bacteria isolated from hot springs to simultaneously produce protease and amylase enzymes. Among ten isolates, the strain T2 was found to be more favorable for amylase and protease. This strain was identified as Anoxybacillus rupiensis (GenBank number: MN252572). Potato peel powder (PPP) was used as a substrate for co-production of amylase and protease from A. rupiensis T2. Experiments were performed under sterile and non-sterile culture conditions. The optimal parameters for co-production of these enzymes were a PPP concentration of 60 g/L, temperature of 50 °C, initial pH of 7.0 and incubation time of 48 h. Under these culture conditions, the amylase and protease activities were determined as 64.9 and 26.2 U/mL in sterile medium. Relatively lower amylase (41.1 U/mL) and protease (14.2 U/mL) activities were attained in non-sterile medium.
- Enzymes play an important role in the biological treatment of animal skin collagen in the leather making process. In this work, three proteases (2709, LimeG and SoakL) with different molecular weight were used in the treatment of cattle hide. Protein and hydroxyproline absorbance was measured to evaluate the treatment effectively. Proteases labeled by Fluorescein Isothiocyanate (FITC) were used to treat the cattle hide to observe the diffusion and reaction behavior of proteases in cattle hide matrix. The results indicate that when the cattle hide was treated with smaller molecular weight protease, the degradation degree of the protein and collagen was more than that of the cattle hide treated with larger molecular weight protease. The fluorescence microscopy images demonstrate that during the early stages, proteases chiefly diffused into the cattle hide matrix through pores and hair follicles, and then diffused into the inner layer via hair follicles to hydrolyze inter-fibrillary proteins for opening up collagen fibers. In the present investigation, a visible assessment for the diffusion and reaction behavior of proteases in the enzymatic treatment of cattle hide matrix was reported.
- Although the loss of scalp hair is distressing and many medical treatments focus on its restoration, the removal of body hair has been adopted since ancient times. Beauty standards, which r eflect the culture of each society, have been presenting the depilated body as absolutely desirable. Through the ages various methods of hair removal have been used depending on the requirements of the individuals. In recent years, Laser and Intense Pulse Light devices have been considered as the most promising solution for excess hair growth, without excluding the efficacy of other methods to induce satisfactory epilatory results. The enzyme-based hair removal method has received little recognition even though experimental and clinical data support its efficacy to provide long term or even permanent epilation. The present review presents these data and examines the likelihood of considering the aforementioned method as ideal.
- Life as we know it heavily relies on biological catalysis, in fact, in a very nonromantic version of it, life could be considered as a series of chemical reactions, regulated by the guarding principles of thermodynamics. In ancient times, a beating heart was a good sign of vitality, however, to me, it is actually the presence of active enzymes that counts... Though we do not usually pay attention, the history of enzymology is as old as humanity itself, and dates back to the ancient times. This paper is dedicated to these early moments of this remarkable science that touched our lives in the past and will make life a lot more efficient for humanity in the future. There was almost always a delicate, fundamentally essential relationship between mankind and the enzymes. Challenged by a very alien and hostile Nature full of predators, prehistoric men soon discovered the medicinal properties of the plants, through trial and error. In fact, they accidently discovered the enzyme inhibitors and thus, in crude terms, kindled a sparkling area of research. These plant-derivatives that acted as enzyme inhibitors helped prehistoric men in their pursuit of survival and protection from predators; in hunting and fishing... Later in history, while the underlying purposes of survival and increasing the quality of life stayed intact, the ways and means of enzymology experienced a massive transformation, as the 'trial and error' methodology of the ancients is now replaced with rational scientific theories.
- This paper describes a kinetic Study of the carbon reactions with oxygen and carbon dioxide (C-O-2 and C-CO2 reaction). The tests were carried out in a thermobalance using carbon from leather shavings char, under isothermal conditions and atmospheric pressure. The experimental results showed a good fit with the Shrinking Unreacted-Core model controlled by chemical reaction, and the Progressive-Conversion model did not describe the process. According to Shrinking Unreacted-Core model, the reaction initially Occurs on the external surface of the particle and the reaction zone moves toward the center of the particle, leaving behind a layer of inert solid (ash). On the other hand, in the Progressive-Conversion model reaction occurs Simultaneously in the entire volume of the particle. The activation energies of the C-O-2 and C-CO2 reactions were determinate, as well as their reaction orders.
- Procedures selected from the work of Bjornsson and Karlsson for the quantitation of sulfated glycosaminoglycans with Alcian Blue were modified and adapted to the measurement of this type of polysaccharide in bovine skin. Modifications include: (1) pulverization of the skin under liquid nitrogen, (2) brief, gentle digestion of the skin with collagenase, (3) the use of a variety of Alcian Blue widely used in histologic work, (4) the recipe for the preparation of the Alcian Blue reagent solution, (5) determination of suitable sample size, volumes of reagent solutions, incubation times, duration of centrifugation, etc. The procedure developed yields linear results for 50-300 mg samples of skin; the relative standard deviation for the procedure is ±15%.
- The leather industry generates highly contaminating liquid effluents with current process methods. In this work, the contamination by nitrogen in wastewater was evaluated for two of the most nitrogen generating steps of beamhouse processing, the soaking and the unhairing/liming steps. Total Kjeldahl nitrogen (TKN), ammoniacal nitrogen (N-NH3), total organic carbon (TOC) and soluble protein analyses were realized from bath samples collected at varying times. It was observed that in long duration soaking, nitrogen liberation to the bath eventually levels out whilst, in unhairing/liming, the nitrogen content did not stabilize even with 27 hours processing. It was possible to observe a relationship between nitrogen liberation, TOC and soluble protein contents of the soaking baths.
- Tanning is the process which converts hide (putrescible) into leather (non-putrescible) material. Tanning wastes contain chrome that is classified as hazardous; consequently, finding satisfactory treatments or proper disposal is a fundamental necessity. Few studies on alternatives treatments for these wastes have addressed the thermal treatment of shavings and trimmings generated during the production process. The ash obtained in this process is rich in chromium oxide, which can be recovered and reused in the tanning process. Firstly, the method consists of obtaining sodium chromate, followed by the production of basic chromium sulfate that can be applied in leather tanning. Preliminary tests were carried out utilizing the tanning salt solution obtained from the ash in tanning hide powder experiments. Two simultaneous analyses were carried out using the product obtained in the laboratory and a commercial product sample, to confirm the efficacy of the salt obtained from the ash. Secondly, the sulfate obtained in the laboratory was applied in the tanning of hide samples, and again two simultaneous analyses were carried out. The results obtained in this work were satisfactory and the typical characteristics of tanned hides were achieved, that is, the hydrothermal stability of the tanned samples and their structure modification (distance between fibers) verified using electron microscopy.
- This work aims to characterize the mechanical and water-resistant properties of gelatin-casein (GC) films modified by microbial transglutaminase (MTG), and to further evaluate the potential application of the mixture of the modified GC films and polyurethane (PU) as coating agents in leather finishing. MTG can improve the mechanical properties (tensile strength and elongation at break) of GC films at the ratios of 2:2, 1:3 and 0:4, and reduce the water absorption. With the increase of MTG concentrations, the elongation at break also increased, but the tensile strength did not change much. The largest elongation at break of the films treated with MTG was obtained at a concentration of 10 U/g-protein. With the increase of PU composition in the GC system, the mechanical properties and water resistance of the films were improved significantly. The PU-GC system was applied as coating agents in leather finishing. The results indicated that the PU-GC11 system (the ratio of gelatin to casein is 1:1) at a ratio of 2:2 (the ratio of PU to GC) was the best coating agent for leather finishing.
- The alternative technologies employed for adding value to bovine hair waste are discussed. The immunization is attained in most hair-saving unhairing technologies by using lime, 1.0-1.5% on weight of salted hides, and with reaction times between 45 and 90 minutes. An extension of the treatment time may result in higher resistance to dissolution by the hair root and the root sheaths due to the action of sodium sulphide, without any improvement in hair protection. The sulphide dose corresponding to the transition from hair saving to hair burning depends on several variables that include duration of the float, lime dosage, pH, temperature, processing time and mechanical action. The action by the alkalis on the hair cuticle and cortex governs the hair degradation and dissolution rate, which is significantly evident at high temperature and especially in the presence of reducing agents. The presence of a reducing agent, such as thioglycolic acid, makes the rupture of disulphide bridges easier, without destroying the protein molecule skeleton.
- The importance of livestock in the production of meat and dairy products, as well as the tannery activity that uses hides and skins as raw material, is widely recognized. However, a considerable fraction of the raw material is discarded or sent to other industries because of its composition or limited value in terms of leather manufacturing. Many studies were conducted to reduce, reuse, recycle or dispose of tanning process waste. Alternatives are being implemented to ensure the adoption of environmentally safe methods that meet environmental laws, and to raise the awareness of the professionals involved in the sector. Brazil reportedly has the largest commercial cattle herd in the world, is the largest producer of bovine cattle in the world and the world's third largest producer and exporter of leather. Other significant data, as well as other indicators of the sector are presented. The present study characterizes the Brazilian industry regarding the leather articles produced, where the footwear articles are the main end-use of leather. A study in 224 Brazilian tanneries was performed with the purpose of finding out which are the most widely used tanning processes. A typical representation of the wastewater treatment technology most frequently adopted in Brazil comprises the stages of preliminary treatment, mechanical and physical-chemical treatment, biological treatment, sludge treatment or disposal and nitrogen removal. The most advanced wastewater treatments and water reuse in tanneries, also the main uses for by-products generated in the leather processing are presented and discussed. The work summarizes the research lines and developments conducted at the UFRGS, at the Laboratory for Leather and Environmental Studies, in order to obtain information on the latest technologies and improvements in the leather sector.
- Previous work from this laboratory demonstrated that films prepared from gelatins that had been enzymatically modified with microbial transglutaminase had improved tensile strength and toughness, were less soluble in water than gelatin alone and had improved hydrophilic properties. In the present study, our goal was to further enhance functional properties of the enzymatically prepared films and at the same time determine if biodegradability is retained. Orienting films has been described as a method to improve mechanical properties. We found that tensile strength, maximum strain, and Young's Modulus improved significantly when orientation took place on either unmodified or crosslinked dry gelatin films or on films that were swollen in water and then were subsequently dried in the strained position. We further demonstrated that the temperature of drying affects mechanical properties; drying at ambient temperature gives products with significantly higher tensile strength and reduced maximum strain over those products that had been dried at a higher temperature. Furthermore, we found that mechanical properties of strained and unstrained films, dried at ambient temperature, will give similar tensile strengths, thus indicating the importance of careful drying in film preparation. Finally, when polyvinyl alcohol was added to the gelatin mixture, films with improved tensile strength and maximum strain were obtained. In all studies, not only was biodegradability demonstrated but it was also found that by enzymatically modifying the gelatin, the resulting products were superior.
- Olein production from the residue constituents of hide pre-fleshing is carried out through the unit operations of extraction and subsequent fractionation of the fatty material (tallow). The residue was characterized and the content of fatty matter (31.83% by mass) revealed a high potential for its reuse. By the extraction/ digestion of tallow assays were carried out to quantify the effect of factors such as the presence of agitation, temperature and extraction time in terms of the efficiency of the extraction operation and acidity index of the tallows obtained. The oils were characterized according to the acidity index, iodine index, saponification index, water content, volatile matter content and fractions of saturated and unsaturated fatty acids. The oil composition was quantified using gas chromatography.
- This chapter provides an overview of how the microorganisms fulfill their nutritional needs and how they extract energy to carry out their life metabolic processes. A heterotrophic bacterium that can grow in a medium containing only glucose as the carbon and energy source, ammonium sulphate as the nitrogen and sulphur source, and a few additional inorganic compounds, has great biosynthetic capability. From these nutritional substances, the microbe can synthesize nitrogenous substances, carbohydrates, and phospholipids. In synthesizing the polysaccharides from monosaccharides, a cell cannot simply glue sugars together. Energy is required to establish the necessary covalent linkages. This energy is in the form of ATP and is expended only inside the cell to energize the monosaccharides. The biosynthesis of the bacterial cell wall peptidoglycan is an endergonic process. It is highly complex and the resulting macromolecule is a rigid cross-linked material that maintains the shape of the bacterial cell.
- In previously reported research from this laboratory, gelatins, both commercial and experimental of varying gel strengths, were chemically modified using glutaraldehyde, glyoxal, and carbodiimide. These classical modifications effectively changed the physical and functional properties of gelatin; however, they have drawbacks in that the crosslinking agents are potentially toxic. Transglutaminase is an enzyme capable of forming inter- or intra-molecular cross-links in many proteins. The enzyme catalyzes an acyl transfer reaction between the γ-carboxamide group of peptide-bound glutamine residues as acyl donors and primary amines as acceptors. When the ε-amino group of peptide-bound lysine acts as acyl acceptor, an ε-(γ-glutamyl) lysine cross-link is formed. This enzyme, now isolated by fermentation, is commercially available, relatively inexpensive, and environmentally safe. We modified gelatins of varying quality with microbial transglutaminase. Gel strengths of low bloom gelatins improved with increasing enzyme concentrations, whereas the gel strengths of higher bloom gelatins either remained the same or decreased with increasing enzyme concentrations. All gelatins gave higher melting points with increasing amounts of enzyme, some even higher than 90°C. Viscosities, measured at 60°C and at or near room temperature, increased with increasing enzyme concentrations. The temperature of gelation, as described in the literature, increased not only with the quality of the gelatin but also with increasing enzyme concentrations. Potential applications for this enzyme in by-product utilization and possibly the leather-making process are numerous.
- Eco-concerns are forcing the leather industry to shift itself from chemical based processing to bio-processing. The use of enzymes for unhairing and bating has been long established and well reported; but the use of α-amylase for fiber opening is a recent development, which advocates the complete elimination of lime. Though the bio-based fiber opening process is established to be an eco-friendly alternative, it is essential to establish its effectiveness versus the conventional liming process by more objective methods. Hence in this work an attempt has been made for quantitative analysis of inter-fibrillary materials viz., proteins, proteoglycans and glycosoaminoglycans (GAGs) released from the skin matrix by the use of complete enzyme based beamhouse process, especially the effect of α-amylase in beamhouse processes. It is observed that treatment of 2% α-amylase for a time period of 180 min is sufficient for the removal of optimum amount of inter-fibrillary materials especially, proteoglycans. Matched pair comparison of experimental bio-based processing has been made with conventional lime based processing and it is observed that the removal of proteoglycans were comparable in both these processes. Also, the crust leathers processed from the matched pair beamhouse processes were compared for their organoleptic and strength characteristics. Both experimental bio-processed leather and conventionally processed control leather were observed to be comparable. This work further authenticates that a completely bio-based beamhouse process is not only eco-friendly but also results in a similar effect on the removal of inter-fibrillary material compared to conventional lime based process.
- One of the great technological challenges of this century is to identify alternative energy sources. The utilization of leather wastes (biomass) to generate energy becomes interesting due to its heating value, as well as for the characteristics of the ash generated, which could be used in other processes such as the production of basic chromium sulfate. Resulting from a partnership between research agencies and private businesses, a semi-pilot unit (350 kW th) was designed and built to process leather wastes. The operation of this semi-pilot unit started in August, 2003. During this period, approximately 200 tons of wastes were treated in over 2,500 h of processing. The semi-pilot unit consists basically of a stratified downdraft gasifier, an oxidation reactor and an air pollution control system (APC). In this paper, the gasifier's emissions were evaluated and the ash and the flue gas were characterized.
- Screening and isolation of a new Bacillus subtilis strain and production of its proteases for leather unhairing are described. B. subtilis strain BLBc 11 was isolated from the aerobic sludge of a tannery. Optimization of enzyme production by this bacterium was carried out using the Plackett-Burman and central composite design. Unhairing and inter-fibrillary removal capabilities were evaluated by scanning electron microscopy and determination of proteoglycans and glycosaminoglycans. Crude enzymatic extracts of B. subtilis BLBc 11 cultures were applied for the unhairing process of hides with excellent results, suggesting that this safe enzymatic preparation can replace the toxic chemicals commonly used in this process.
- The use of biotechnology by tanneries has increased in recent years. Enzymes can be applied during different steps of the leather production process: soaking, dehairing, bating, dyeing, degreasing or in effluent and solid waste treatment. This study evaluated the performance of five commercial enzymes in soaking and unhairing/liming by comparing the chemical and coenzymatic processes. Tests were conducted in bench drums to evaluate the action of enzymes during each stage. Concentration, processing time and type of enzyme were varied. Total organic carbon and soluble protein were used to measure the efficiency of the processes. Enzymatic activity assays on collagen, keratin and lipid and scanning electron microscopic (SEM) analyses of hides were used to complement the study. Coenzymatic processes generally showed better results in comparison to chemical processes. The enzymes showed activity on all substrates, and the SEM analyses of the hides showed a clear difference between the chemical and coenzymatic processes.
- REVIEW: Living organisms encountered in hostile environments that are characterized by extreme temperatures rely on novel molecular mechanisms to enhance the thermal stability of their proteins, nucleic acids, lipids and cell membranes. Proteins isolated from thermophilic organisms usually exhibit higher intrinsic thermal stabilities than their counterparts isolated from mesophilic organisms. Although the molecular basis of protein thermostability is only partially understood, structural studies have suggested that the factors that may contribute to enhance protein thermostability mainly include hydrophobic packing, enhanced secondary structure propensity, helix dipole stabilization, absence of residues sensitive to oxidation or deamination, and increased electrostatic interactions. Thermostable enzymes such as amylases, xylanases and pectinases isolated from thermophilic organisms are potentially of interest in the optimization of industrial processes due to their enhanced stability. In the present review, an attempt is made to delineate the structural factors that increase enzyme thermostability and to document the research results in the production of these enzymes.
- In a moment that amazingly advances are being reached on the development of technologies to obtain high value chemical compounds as polymers, fine chemicals, pharmaceutical industry intermediates and chemical entities, we cannot refuse that a meaningful progress is due to the maturing in knowledge of biological transformations. Biocatalysis and biotransformations are being widespread applied to generate processes and products with incredible success. In this review article we present the main contributions of biotechnology and biological catalytic processes to Chemistry, the most important evolution steps on enzymatic transformations, how it has being applied and which are the perspectives to academic and industrial environments. We also would like to stimulate the community to step out research in biotechnology applicable to chemical and pharmaceutical industries, trying to achieve what we believe to be the ideal layout: integrating chemical transformations, enzymatic conversions and fermentation processes.
- The enzymatic treatment of hides in tannery processes is a promising technology. However, the reaction kinetics of commercial enzymes available to the leather industry are not fully understood and their activities have been mainly determined with model proteins such as casein as substrate, which are not of direct relevance for cattle hides. Therefore, it is important to determine their activities on collagen and keratin, the main proteins of skin, in order to use these enzymes in leather processing. This work describes the study of five proteases, used commercially in tanneries, to assess their ability to act upon collagen and keratin and to determine their unhairing. Results showed that all commercial enzymes tested had more activity on collagen than on keratin. Unhairing was also tested and four out of the five enzymes tested showed some unhairing activity. Optima of the temperature and pH of the enzymes were very similar for all five enzymes, with maximal activities around 55ºC and pH 9 to 12, respectively.
- One of the numerous possible solutions to the problem of chrome-tanned wastes is their enzymatic dechromation, which has been dealt with in detail in a number of publications1-10. When seeking ways of processing chrome-tanned wastes in the Czech Republic we decided to employ the enzymatic dechromation technology worked out at the USDA in Philadelphia11. To fit conditions in the factory manufacturing auxiliary tanning agents where the technology was applied, we modified the American process by using organic volatile bases such as isopropylamine, diisopropylamine, cyclohexylamine, ammonia and others
- Décorin is a minor proteoglycan (part protein and part carbohydrate) of the skin that is among the key components that undergo changes and removal during conversion of hides to leather. The majority of décorin removal takes place during the dehairing of hides, either traditionally with sodium sulfide or by an alternative oxidative dehairing procedure. The oxidative dehairing method using sodium hydroxide and percarbonate, developed by Marmer and Dudley, was utilized. Further removal of décorin by exposure to proteolytic enzymes during pretanning was explored to study the effects on the quality of leather. Additional removal of décorin was observed when an alkaline protease was added during the reliming stage and pepsin was added during the pickling stage in the pretanning treatments of the hides. More pronounced improvement in leather quality, due to more décorin removed, was observed in oxidatively dehaired hides than those dehaired traditionally with sulfides. As the décorin content decreased, the leather product became softer, more stretchable, and tougher than the control leather tanned without adding proteolytic enzymes. Employing the alternative oxidative dehairing process can solve the problem of sulfide toxicity to the environment while at the same time improving the quality of leather if co-treated with proteolytic enzymes.
- The laboratory trials of a process to treat untanned leather waste to isolate valuable protein products are presented. In this comparative study, both thermal and enzymatic treatments of leather waste were performed. The enzymatic method utilizes commercially available alkaline protease at moderate temperatures and for short periods of time. The concentration of the enzyme was 500 units per gram of leather waste which makes the method cost-effective. Amino acid composition in the hydrolysate obtained by the enzyme hydrolysis of untanned leather waste is determined. Chemical and physical properties of protein powder products from untanned leather waste were evaluated by spectrophotometric and chromatographic methods and by use of electron microscope. The results of microbiological assays confirm that these products agree to food safety standards. This relatively simple treatment of untanned leather waste may provide a practical and economical solution to the disposal of potentially dangerous waste.
- The article presents the final research into the system containing NaOH, Na2S, and a salt such as NaCl. Na2SO4 or Na2HPO4 and their influence on the properties of pelt and leather, Here are two main points of the investigations: the establishment of dermatan sulphate changes during unhairing and the microscopy investigation. It was established that the unhairing method influences the amount of dermatan sulphate in pelt. The method for dermatan sulphate determination was developed and used in this research. The results show that a strongly alkaline action does not increase the removal of dermatan sulphate. As collagen's chemical and physical changes could be reflected in its structure, optical and scanning electron microscopy analyses of pelt and leather grain and corium were carried out. The micrographs show that the structure of pelt and leather depends on the unhairing method and it differs - differences in opening-up level are observed, These differences are clearly visible and depend on the method of unhairing. The microscopy images confirm the importance of the role of salts. which are added to the unhairing system NaOH + Na2S.
- The effects of the combination of immobilized lipases from Thermomyces lanuginosus (TLL) and Rhizomucor miehei (RML) on the transesterification (ethanolysis) and hydrolysis of soybean oil, a heterogeneous substrate composed of different fatty acids, were investigated. The influences on the yields of conversion of the substrate molar ratio, enzyme content, and the ratio of TLL and RML in the mixture of the biocatalyst were analyzed using the central composite design and the response surface methodology. The optimal conditions for transesterification obtained were: substrate molar ratio of 7.5:1 ethanol:soybean oil; enzyme content of 25% (weight of oil); and 80% of TLL in the mixture of biocatalysts. For hydrolysis, the optimal conditions were: substrate molar ratio of 3:1 water:soybean oil; enzyme content of 25% (weight of oil); and 65% of TLL in the mixture of biocatalysts. Under the optimal conditions, the yields of conversion were 90% for transesterification and 95% for hydrolysis. Time courses of the reactions showed that when using the optimal mixture of lipases, the yields were higher than those obtained using only one of the enzymes, approximately 15% higher than using only TLL and more than twice than using only RML. Enzyme activities remained unaltered for both transesterification and hydrolysis, even after ten reaction cycles in which the immobilized enzymes were washed with n-hexane at the end of each batch. The use of a mixture of immobilized lipases seems to be a promising technology in order to improve the enzymatic synthesis of biodiesel and hydrolysis of oils.
- Alkaline proteases are of considerable interest in view of their activity and stability at alkaline pH. This review describes the proteases that can resist extreme alkaline environments produced by a wide range of alkalophilic microorganisms. Different isolation methods are discussed which enable the screening and selection of promising organisms for industrial production. Further, strain improvement using mutagenesis and/or recombinant DNA technology can be applied to augment the efficiency of the producer strain to a commercial status. The various nutritional and environmental parameters affecting the production of alkaline proteases are delineated. The purification and properties of these proteases is discussed, and the use of alkaline proteases in diverse industrial applications is highlighted.
- A bacterium which secreted natural leather powder-degrading protease was obtained by successive screening using media containing white meal, gelatin, and leather powder. The selected and isolated strain (PN-13) belongs to the family of Bacillus. A protease (PN-13 protease) secreted by the Bacillus sp. PN-13 was purified from culture supernatant. The protease was homogeneously purified and the molecular mass was estimated as 30kDa. The protease hydrolyzed casein, gelatin, and especially leather powder effectively under alkaline conditions.
- Leather processing has been an important light industry in China, which has contributed a lot to economy. The recent environmental challenges caused tremendous pressure to leather manufacture. The conventional beam house processes employ a wide range of chemicals which result in more than 60% of the total pollution in leather processing (mainly based on COD, BOD, TS, SS, NH3–N). In this study, cleaner beam house processes were tested on cattle sofa leather to provide a clean environment. A control experiment was run parallel using conventional beam house processes. The results show that the de-hairing is complete through pelt histological microstructure, the extent of opening up of fibre bundles is very good, which is substantiated through chrome distribution analysis, scanning electron microscopic pictures of wet blue leathers and the analysis of contents of total proteins, polysaccharide and hydroxyproline in composite liquor, and the performance of the leathers is shown to be satisfied with the quality standard of sofa leather. The results from composite water analysis show that the cleaner processes enjoy in the reduction of emission water, chemical oxygen demand, total solids and ammonia-nitrogen loads by 46%, 93%, 58% and 54%, respectively, compared to the conventional processes. The total dry sludge from the clean processes is almost eliminated, and the composite cost is decreased by 10%.
- The use of enzyme based products for many areas in leather making has found its way into commercial practice. Proteolysis and α-amylase enzymes have found use in hair removal and fiber opening, producing comparable results to the conventional practice of lime and sulfide based dehairing and fiber opening. However, this process is a two step sequence in which dehairing is performed by the proteolysis enzyme followed by fiber opening through α-amylase. This study aims at transforming the two-step method into a single-step process, while maintaining environmental sustainability. Experiments were carried out using various percentages of dehairing enzyme and α-amylase following successive, simultaneous addition. The order of addition of the enzymes is also varied. Standardization experiments at bulk level were carried out to obtain best results. The leathers obtained from simultaneous addition of enzymes (1% protease and 0.75% α-amylase) were comparable to that of the conventionally produced leathers in terms of physical properties and appearance. The input-output analysis shows complete dehairing and fiber opening, which is also confirmed through scanning electron micrographs. There is reasonable reduction in water consumption, wastewater discharge, COD and TS loads when compared to the conventional leather processing.
- Growing global concern on environmental health is forcing all the processing industries to adopt greener and cleaner manufacturing practices. Thus, the leather industry is being pressurized to look for cleaner leather processing. The conventional method of leather making involves do–undo logic. This results in the emission of a huge amount of pollution load such as biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total solids (TS). Currently tanners are looking for design and utilization of cleaner and safer technologies. In this approach, a process has been designed to limit the pH range in leather processing from 13.5–2.8 to 8.0–3.8. An experimental process has been developed by combining enzymatic unhairing, enzyme based fibre opening and pickle and basification free chrome tanning. The experimental tanning process provides comparable leather quality with reduced environmental impact and effluent treatment costs. The process explored also appears to be economically viable.
- Currently, 80–90% of leather production uses chromium tanning; thus, the trimmings and shavings resulting from the manufacturing of leather goods create a waste with a high pollution potential. One alternative for handling this scrap-leather waste is thermal treatment (gasification and combustion). The ashes generated during this process are rich in chromium, containing between 50% and 60% chromium oxide (Cr2O3) by mass, and the ashes can thus potentially be utilized as a source of chromium for the synthesis of sodium chromate (Na2CrO4). With the aim of improving on the results of previous attempts made to recover chromium from these ashes, in this work, the use of sodium nitrate to oxidize the trivalent chromium to the hexavalent form was studied. The resulting conversion of chromium (III) to chromium (VI) achieved was over 94%, and the sodium chromate obtained from the ashes showed physical properties similar to the commercial product.
- One of the methods to decrease the pollution of tanneries' wastewater is hair saving unhairing of hides. An investigation of proteolytic activity of enzymatic preparation (EP) has shown that some EPs have high stability in strong alkaline solutions and can be used for the hair saving process.Based on this investigation, a new hair saving unhairing method using a system containing EP, sodium hydroxide, sodium sulphide, and disodium hydrophosphate was developed. The method results in a high quality pelt suitable for leather manufacturing, decreases the pollution caused by sodium sulphide and the other products of hair degradation and avoids the pollution caused by calcium compounds.
- The leather industry is a heavy pollution industry and looking for clean technology. The utilization of enzyme and ultrasound in the industry are potential eco-friendly technologies.Enzymes can degrade the untanned solid leather waste. According to our investigation, ultrasound (40 kHz, 0.64 W/cm2) has little effect on the activity of one alkaline protease from Bacillus licheniformis. It is the first time to use ultrasound to accelerate the enzymatic hydrolysis of the untanned solid leather waste. With the application of ultrasound, the value of kA for the enzymatic hydrolysis of the untanned solid leather waste increases 18% and KM is almost unchanged, compared with that obtained without ultrasound. Ultrasound improves the ultimate conversion ratio from 57.6% to 84.1%. The reason is that ultrasound can facilitate the protease through the pores of skin and impair the integrity of collagen. Amino acid analysis indicated that ultrasound can promote the breakdown of helical regions of collagen which are difficult to attack by proteases.In view of environment protection, the use of enzyme and ultrasound in combination is a promising clean technology for the disposal of the untanned solid leather waste.
- In leather industry, unhairing is a heavy pollution operation. The conventional lime–sulfide process produces a large amount of sulfide which is toxic to health and difficult to dispose. Moreover, conventional lime–sulfide process leads to the destruction of the hair causing increased COD, BOD and TDS loads in the effluent. As an alternative method, enzymatic unhairing is a promising clean technology. The main utilized enzyme preparations are proteases.There are many reports about enzymatic unhairing, most of which are qualitative. The kinetics of enzymatic unhairing by protease was discussed in this article. It will provide useful information to enzymatic unhairing. In our research, by analysis of the concentrations of released total protein in enzyme bath during protease unhairing, the good linearity between released total protein and square root of time (min1/2) was obtained at the initial stage. The good linearity suggests that enzymatic unhairing by protease is a diffusion-controlled process at the initial stage. The analysis of kinetics of released saccharides also confirms the same conclusion. On the other hand, the same characteristics between the kinetics of released saccharides and that of released total protein further confirms that it is the hydrolysis of core protein by protease that leads to the degradation of proteoglycans and the release of protein and saccharides. However, in our tests, the kinetics of released collagen indicates that the injury to skin took place in 3–6 h. Therefore, it’s necessary to control the time of protease unhairing within an appropriate limit.
- Leather processing has been an important industrial activity, which has gained significant economic relevance in India. The recent practices of leather manufacture cause difficulties with regard to environmental challenges. The conventional method for making the skins ready for tanning and the tanning by itself employs a wide variety of chemicals which result in an increase in chemical oxygen demand (COD), total dissolved solids (TDS), chlorides, sulfates and chromium in the tannery effluent. In this study, an integrated chemo-enzymatic methodology has been explored which would minimize or to some extent eradicate the unsafe chemicals involved in the process to provide a clean environment. The sequence involves an enzymatic dehairing, NaOH based fibre opening and a pickle-less chrome tanning. The modified process results in decrease in COD and TS (total solids) loads by 67 and 78%, respectively, as compared with control process. The process explored appears to be economically viable.
- The heterogeneous complexity of sludges and wastewaters has created gross uncertainty and deviations in predictions of suitable models for their measurement. At the same time, it is becoming increasingly obvious that the current paradigms and ideologies are wrought with problems and limitations suggesting the need to move to a more consolidated analytical objective evaluation. Rapid developments in understanding activated sludge processes and wastewater remediation warrants exploitation of different strategies for studying their degradation. It is time to replace subjective terms like sludge volume index (SVI), zone settling velocity (ZSV), filament index (F I), fractal dimension (D), flocculating ability, surface charge (ζ), degree of hydrophobicity, chemical oxygen demand (COD) with a mathematical one that can provide an absolute quantitative relationship for the properties of wastewater and/or a sludge floc. There are no current objective values that can be introduced to represent the plethora of biological remediation terminologies such as bioleaching, biosorption, bioaugmentation, biostimulation, biopulping, biodeterioration, biobleaching, bioaccumulation, biotransformation and bioattenuation. Enzyme technology has been receiving increased attention and this review focuses on the latest developments on the enzymology of biological remediation. It discusses the present pitfalls with current strategies and suggests that sludge–floc parameters, such as internal structure and composition, sludge retention time, microbial ecology, nutrient concentration, dissolved oxygen and type of industrial wastewater, whether from an aerobic or anaerobic system, are replaced by quantitative kinetic terms (K m , V max , K cat) associated with the enzymology of the sludge floc and/or wastewater.
- Three keratinolytic Bacillus spp. isolated from the Brazilian Amazon basin were characterized. The strains P6, P7 and P11 were identified based on morphological and biochemical characteristics and 16S rDNA sequences. P6, P7 and P11 sequences shared more than 99% similarity with B. subtilis, B. amyloliquefaciens and B. velesensis. The keratinases produced by these bacteria were active on azokeratin and degradation of feather barbules was observed. The enzymes were inhibited by the serine protease inhibitor PMSF, and showed maximum activity at pH 9.0. Proteins like albumin, casein and gelatin were hydrolysed by these keratinases. Depilatory studies on bovine pelts revealed that all three strains were efficient in promoting de-hairing. Microscopic analysis showed that the epidermis was completely removed and the absence of hair in follicles was observed.
- Defatted raw and roasted peanut flour were hydrolyzed with alcalase or sequentially with pepsin and pancreatin, and then the hydrolyzates were fractionated by RP-HPLC and tested for hypotensive potential. This research revealed that proteolytic peanut digests have an inhibitory effect on the activity of angiotensin converting enzyme (ACE). Three fractions from the hydrophobic end of the chromatogram of each hydrolyzate were the most potent for inhibiting ACE activity in comparison to seven other fractions. These potentially potent fractions were then assayed for IC50. Fractions from the alcalase digestion of raw peanut exhibited IC50 values of 8.7–122 μg/ml, and those from roasted flour exhibited values of 12–235 μg/ml. IC50 values of 7.9–65.9 μg/ml, and 11–36 μg/ml for raw and roasted peanut, respectively, from the pepsin–pancreatin system were observed. These values compare to the IC50 value of 0.36 μg/ml of a known commercial ACE inhibitor (pGlu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro).
- Enzymes have provided a focus for the chemist to design a range of prodrugs to release cytotoxic agents already in use in the cancer clinic and those which had been candidates in the past, based on their efficacy in preclinical studies, but discarded because of their toxicity to normal tissues. The specificity of enzyme reactions provides the means to limit prodrug activation to the tumour site, through enzyme targeting by chemical conjugation or genetic fusion to tumour associated antibodies (ADEPT), or via enzyme gene delivery systems into tumour cells (GDEPT). The substrate tolerance of many of the enzymes used has also meant that a variety of prodrug/drug combinations can be assessed using the same enzyme reaction. It is the flexibility provided by the choice of enzyme, the range of tumour antigen targets and the prodrug chemistry that makes ADEPT such an exciting prospect for the future of cancer treatment and the more recent extension of the enzyme/prodrug concept to a gene therapy approach provides a second avenue for success.
- Cultural conditions for the production of lipase by Aspergillus niger strain MTCC 2594 by solid-state fermentation using gingelly oil cake were standardized. A lipase activity of 363·6 U/g of dry substrate was obtained at 72 h under optimum conditions. Addition of various nitrogen sources, carbohydrates and inducers to the substrate was found to be ineffective. The enzyme was optimally active at pH 7·0 and 37°C, and was found to be stable between pH 4·0–10·0 and 4–50°C. The enzyme also showed remarkable stability in the presence of detergents and it could be effectively used for the removal of triglyceride soils in laundry.
- In tanneries, the phases of conditioning and preparing the hide for tanning, as well as the transportation and fixation of tanning substances, are all carried out in aqueous media. Most of the steps of these processes are carried out with fresh water, which is used as a vehicle for the diffusion of chemical products and the extraction of undesirable materials from the hide. The objective of this study is to provide the minimization of water consumption at tanneries by applying the reuse of water at some stages of the process. Alternatives for water reuse were evaluated through analysis of the process wastewater to determine the concentration of some contaminant parameters. In tests with half-hides, the possibility of reusing the liquors from the 2nd bating washing in the 1st bating washing, and of reusing the liquors from the pre-deliming washing in the pre-deliming operation, was verified. In industrial scale the water reuse from a mixture of bating washings in the deliming and deliming bating was tested successfully. The quality of wet-blue leather analyzed in the systems with and without water reuse did not show any considerable differences and satisfies the tannery specifications. Finally, a mathematical program for mass integration was applied to solve the problem of water reuse in the beamhouse steps.
- A novel protease produced by Bacillus cereus grown on wool as carbon and nitrogen source was purified. B. cereus protease is a neutral metalloprotease with a molecular mass of 45.6 kDa. The optimum activity was at 45 °C and pH 7.0. The substrate specificity was assessed using oxidized insulin B-chain and synthetic peptide substrates. The cleavage of the insulin B-chain was determined to be Asn3, Leu6, His10-Leu11, Ala14, Glu21, after 12 h incubation. Among the peptide substrates, the enzyme did not exhibit activity towards ester substrates; with p-nitroanilide, the kinetic data indicate that aliphatic and aromatic amino acids were the preferred residues at the P1 position. For furylacryloyl peptides substrates, which are typical substrates for thermolysin, the enzyme exhibited high hydrolytic activity with a Km values of 0.858 and 2.363 mM for N-(3-[2-Furyl]acryloyl)-Ala-Phe amide and N-(3-[2-Furyl]acryloyl)-Gly-Leu amide, respectively. The purified protease hydrolysed proteins substrates such as azocasein, azocoll, keratin azure and wool.
- Proteolytic enzyme isolated from Aspergillus tamarii prepared by solid state fermentation was studied for dehairing of goat skins in the tannery. The stability of the enzyme for dehairing was optimized at different environmental parameters. Unhairing of goat skins could be obtained at pH 9–11 and temperatures 30–37°C with enzyme concentration of 1% w/v and incubation periods of 18–24 h. The physical properties of the experimental leathers in comparison with the control sets gave better results with respect to tensile strength and elongation at break.
- Concern about pollution related problems in the global scenario are persuading all the processing industries to adopt cleaner manufacturing practices. Thus, the leather industry is also under pressure to look for effective alternative tanning materials for chromium. Natural products like vegetable tannins are regaining importance. However, there are limitations in the use of vegetable tanning materials because of its high organic load in the effluent, which are difficult to degrade leading to high chemical oxygen demand (COD). Moreover, conventional vegetable tanning process requires partial pickling that involves the use of sodium chloride, to suppress osmotic swelling. This results in very high amount of total dissolved solid (TDS) content in wastewaters. In this investigation, an attempt has been made to design an eco-friendly vegetable tanning process combining pickle-free tanning and application of proteolytic enzymes to improve the exhaustion of vegetable tannins. Such an approach has resulted in more than 95% tannin exhaustion in the case of the experimental process, an increase of 10% compared with the conventional vegetable tanning process. The tanned leathers showed slight improvement in hydrothermal stability. Physical and tactile evaluation of experimental leathers has been better than conventionally tanned leathers. Surface colour values illustrated negligible variation in colour and shade between control and experimental leathers. The resultant leather showed opened up, split compact fibre structure that has been well coated, indicating that the enzyme assisted tanning process did not bring about any major change or destruction on the fibre structure of the leathers. The optimized system has been field tested in a commercial tannery. The results showed that the enzyme assisted tanning process is efficient in terms of improved quality of leather and also led to reduction in total solids (TS), chlorides and COD loads. The enzyme assisted tanning system presented appears to be a viable option for combating pollution arising from the conventional vegetable tanning system.
- In this work is described the isolation of a new proteases-producing strain of Bacillus subtilis, screened from aerobic tannery sludge, to be applied in leather production. The optimization of culture conditions to enhance the proteolytic activity was carried out using central composite design. The enzymatic extract was characterized and the hide unhairing and the inter-fibrillary removal capabilities of the enzymatic extract were evaluated by scanning electron microscopy and by the determination of proteoglycans and glycosaminoglycans. The leather quality obtained with this enzymatic preparation was assessed for possible damages to hide collagen by measuring the amount of hydroxyproline released into the reaction medium. Temperature was the most significant factor for culture conditions optimization. The crude enzymatic extract showed the best values for proteolytic activities at pH 9 and 10, temperature between 37 and 55 °C, and showed good thermal stability up to 45 °C. The treated hides presented few remaining hairs; for the enzymatic process, the removal of inter-fibrillary proteins was approximately fourfold for glycosaminoglycans and sixfold for proteoglycans, when compared with the conventional unhairing process. The enzyme application was successful for hide treatment, suggesting that this enzymatic preparation can be used in an environment-friendly leather production to replace the conventional chemical process.
- Leather wastes tanned with chromium are generated during the production process of leather, hence the wastes from hand crafted goods and footwear industries are a serious environmental problem. The thermal treatment of leather wastes can be one of the treatment options because the wastes are rich in chromium and can be used as a raw material for sodium chromate production and further to obtain several chromium compounds. The objective of this study was to utilize the chromium from leather wastes via basic chromium sulfate production to be subsequently applied in a hide tanning. The obtained results have shown that this is the first successful attempt to achieve desired base properties of the product. The result was achieved when the following conditions were applied: a molar ratio between sodium sulfite and sodium dichromate equal to 6; reaction time equal to 5 min before addition of sulfuric acid; pH of sodium dichromate solution equal to 2. Summarizing, there is an opportunity to utilize the dangerous wastes and reused them in the production scheme by minimizing or annulling the environmental impact and to attend a sustainable process development concept.
- An extremely alkaliphilic bacterial strain, Bacillus sp. PPKS-2, was isolated from rice mill effluents and screened for the production of extracellular keratinase. The maximum production of keratinase occurred after 48 h in shaking culture at pH 11.0 and 37 degrees C in a medium containing 0.5% soybean flour. The strain grew and produced alkaline keratinase using chicken feather and horn meal as the sole source of carbon and nitrogen. An addition of 0.1% soybean flour or feather hydrolysate and sodium sulfite to feather medium increased the production and complete solubilization of feather took place within 5 days under solid-state fermentation conditions. The partially purified enzyme displayed maximum activity at pH 11.0 and 60 degrees C in a broad range of NaCl, 0-16%, and was not inhibited by sodium dodecyl sulfate (10%), ethylenediaminetetraacetic acid (10 mM), H2O2 (15%), and other commercial detergents. Immobilization of the whole cells proved to be useful for continuous production of keratinase and feather degradation. The enzyme was effectively used to remove hair from goat hide. The strain PPKS-2 can be effectively used for solid waste management of poultry feather in submerged as well as solid-state fermentation.
- To characterize the secretion of proteolytic activities against keratin, collagen and elastin in liquid cultures of Bacillus cereus IZ-06b and IZ-06r isolated from wool. Growth of B. cereus IZ-06b and IZ-06r were characterized in batch culture. Both strains needed an organic nitrogen source, were able to grow on wool or peptone as sole carbon and nitrogen sources, and metabolized glucose, maltose and other simple sugars. Proteolytic activities were investigated in batch cultures grown in peptide-restricted, carbon-sufficient medium. Secretion of proteases was induced by peptide limitation while different proteolytic activities appeared sequentially in the growth medium. When the most available components of the peptone were depleted, collagenolytic and elastolytic proteases were produced. These were later replaced by the production of keratinolytic protease. B. cereus can adjust its proteolytic affinity profile in response to the supply of organic nitrogen and sequentially secrete proteases with activities targeted against increasingly inaccessible proteinous substrates as the nutritional availability in the environment deteriorates. Peptide-limited, carbon-sufficient growth media containing no proteinous substrates are well suited for protease production in B. cereus while growth conditions can be adjusted to optimize the proteolytic affinity profiles.
