 |
|
|
|
|
|
| Home > Articles > Golden wave in detergents |
|
|
Golden wave in detergents |
| ...Continued from page1 |
|
|
Efforts are on to manufacture enzymes that can work below the normal temperature range of 30C to 40C to save energy. It has been observed that energy consumption per wash in household washing machine (3 kg clothes) at low temperature (30C) is less than 1 % of the energy used at a higher temperature (60C) (Edvardetal, 1991).
Cellulases
These enzymes introduced in the late 1980s were described for the first time in a Japanese patent filed by Murata. These enzymes are used in UK and US since 1991. Cellulases remove microfibrils from cotton and cotton-blended fabrics. These microfibrils stick out from the main fibre of cotton and are formed during use and repeated washing condition of the tissue. This makes garments and household textiles unusable. The cellulases can be used as softening agents, to remove soil particles and to revive colours.
The overall cellulose structure has two types of region; one that has a higher order of crystallinity is called crystalline region. The other type has less structured order, and hence is called as amorphous regions. The activating but not hydrolytically acting enzyme was named as C i-activity. According to this concept, microorganisms that are able to degrade crystalline cellulose have C i-activity. This enzyme is not present in that microorganism that attack only substituted cellulose like carboxymethyl cellulose as they have Cx-activity.
According to a recent research, biodegradation of cellulose requires the interaction of three different hydrolytes or at least the first two enzymes to attack simultaneously. These include:
· Cellobiohydrolase is also called as exocellulase (C i-activity)
· Endoglucanases is also called as Endocellulases (C i-activity)
· ß-Glucosidase is also called as cellobiase
It was observed that sebum in the interior of cotton fibres cannot be removed by ordinary detergents satisfactorily, although they readily remove sebum on the exterior of the fibres. Alkaline cellulase interacts selectively with cellulose in interfiber spaces in the interior of fibre, and selectively removes the sebum soil. The removal of the soil is by the hydrolysis of amorphous regions (Murata et al, 1991).
Cellulases can be chemically modified to have greater stability and efficiency in alkaline medium. It can be done by treating the acid cellulases with reagents like maleic anhydride (Bund and Singhal et al, 2002).
Currently, the cellulases used in detergents are manufactured from bacteria and fungi. Bacterial cellulases have been in use since 1987, for example, Biotex. Some genetically engineered strains, which are widely used include Streptomyces sp. KSM-2, Bacillus KSM-635. The fungal cellulase from Humicola isolens DSM1800 is active under mild alkaline conditions.
Miscellaneous detergent enzymes
Peroxidases:
These are one of the newest classes of enzymes that have been included in detergent formulations. Peroxidases are subclass of general oxidoreductases and are very popular and commercially available for manufacturing detergents. Novo Nordisk produces this under the brand name Guardzyme obtained from mushroom Corprinus cinereus. It is a heme containing protein, which in the presence of H2O2 can mediate the oxidation of fugitive dyes in solution and inhibits the dye transfer.
Pullulanases:
In recent years, pullulanases (Pullulan 6- glucanohydrolase) a debranching enzyme has been gaining importance due to its efficiency of starch hydrolysis by cleaving a-1, 6 linkages. Pullulanases with other amylolytic enzymes are used in detergents for improved stain removal and enhanced overall cleaning performance. This enzyme was first isolated in Klebsiella pnuemoniae (Shaw et al, 1995).
Manufacturing and downstream processing
Nearly all-detergent enzymes, which are used and marketed today, are produced through large-scale fermentation of microorganisms. Most of enzymes "are obtained from the bacterial or fungal strains. As low cost enzymes are needed to support the requirements of the global detergents business, enzyme manufacturers should consider the following points to ensure lower costs:
· The enzyme-producing micro-organism must be capable of secreting the enzyme extra-cellularly in the bulk fermentation broth, as the cost in terms of both money and time to recover enzyme from the fermentation broth is very high
· The production organism should be able to produce highest possible yields. Strain optimisation can be accomplished either through classical mutagenesis and screening methods or using genetic engineering
· The number of steps in the downstream processing should be kept to a minimum to be economical and also to avoid yield losses
· The production organism should produce the desired enzyme in a highly pure state without any contaminating side activities or proteins. This can be done by deleting the genes, which codes for unwanted enzymes and proteins
Enzyme formulations
Enzymes are formulated mainly in two forms, as a liquid product or as a granular product.
Liquid product formulation
The highly concentrated liquids of the evaporator or the ultra filtration unit can be used for the manufacturing of the liquid formulations. The liquids, which are to be incorporated into the formulation, must be sterilized against microbial growth. Stabilizing agents like borax, organic boric acid derivatives, alkali salts, etc should be added along with preservatives like urea, propel glycol, diglycol, and sorbitol. The current trend is to formulate these liquid formulations as structured liquids with the help of salts and polymers, so that all surfactant remains in the structured liquid and enzymes remains in the aqueous phase. (Hermann et al, 1997).
Granular enzyme products
Highly ultrafiltered and dialysed enzyme solution is subjected to adjustment of pH, turbulences, and temperature in the suitable range, when the enzyme crystallises out. It can be precipitated at high salt concentrations. The following four types of granulation process are employed:
Enzyme pulling:
The enzyme (dry) is dispersed into a molten wax, non-ionic surfactant, or polymer matrix, and then sprayed in a cooling tower to form solid, spherical, molten water-soluble or water dispersible material with a melting point above 50C. This technique offers the advantages of high throughput and ability to recycle particles that fall outside the desired size range but has a drawback i.e., the particle has relatively poor physical strength, leading to break- up and high dust generation in subsequent processing. Polyethylene glycols can be used to improve physical strength and thus lesser dust formation, but as particle break-up cannot be completely ruled out, it is not used widely at present.
Granulation by extrusion process:
In this technique, all the ingredients like enzyme powder or liquid concentrate with binders, such as clay sugar, starch, some anti-clogging agents like cellulose fibres and solubility enhancers like sodium sulphate are mixed together and an extrudable dough is produced, which is then pressed through the perforated metal plate. The extruded noodles are cut into small cylinders and then given a round shape by an spheroniser. After sieving, the particles are coated with pigments such as titanium dioxide, and protective outer layers to achieve desired appearance and to improve granulate integrity. The drawback of this method is the high capital investment in a multi-step process and the sensitivity of the process variation in feedstock moisture and composition.
High shear granulation:
In this process the enzyme is mixed with controlled amounts of water, binders such as polyethylene glycol, ethoxylated fatty alcohols, fatty acids, bentonite, waxes having low melting temperature and other granulating agents so as to form a low-moisture agglomerate. This agglomerate is then passed on to the high-shear mixer in which it is broken up into smaller particles. The particles are then dried in a fluidised bed and coated with a final protective layer and pigments like titanium dioxide.
Fluid bed coating:
In this process, on the inert support or core material like sodium chloride, calcium alginate, urea, or saccharose beads, liquid enzyme is sprayed and the coating material is transferred to the drying zone with the help of heated air stream. Then once the enzyme layer has dried, additional coatings of stabilizers, chelating agents, antioxidants and pigments are applied. The outer coating consists of film forming polymer such as titanium dioxide. The volume of flow for proper fluidization is dependent on the surface area and the shape & density of the core material. The proper fluidization should flow sufficient core material through the spray zone to coat all the atomized liquids on to the core material to prevent spray drying.
Conclusion
As in the other sectors of the chemical process industry, where enzymes are increasingly playing a crucial role in making conventional processes more environment-friendly, the detergents industry has also benefited from the introduction of enzymes. The enzyme detergents are proving to be better than the traditional detergents with respect to washing performance, but there are still few constraints like the inability of the enzymes to withstand high alkalinity and variable temperatures. However, these hurdles are likely to be overcome in the near future with newer & better technologies, which would open up a wide array of opportunities for the detergent enzymes industry.
|
|
|
|
|
| Posted : 8/29/2005 |
|
|
|
| |
|
|
|