The original idea of using enzyme as detergents was described in 1913 by Dr Otto Rohm, who patented the use of crude pancreatic extracts in laundry pre-soak compositions to improve the removal of biological stains. In the same year, the first enzymatic detergent named Burnus was launched, but was not popular because of its own limitations. Subsequently, Bio- 40 - a detergent containing a bacterial protease was produced in Switzerland and launched in the market in 1959 and it gradually became popular. In the period from 1965 to 1970, use and sale of detergent enzymes grew very fast. In 1970, the use was distorted due to dust production by formulations leading to allergies to some workers. This problem was overcome in 1975 by encapsulating the granules of enzyme. From 1980s to the 1990s, several changes took place in the detergent industry like development of softening through the wash, development of concentrated heavy-duty power detergents, development of concentrated or structured or non- aqueous liquid detergent (Ee et al, 1997).
Presently, detergent enzyme has become an integral part of detergent formulation. A look at the market share of detergent enzyme indicates it to be very high in comparison with other enzyme applications. Enzymes that have to be used as detergent composite must possess the following characters:
·Stability at temperature over a broad range of 20C to 50C and even above
·The optimum pH should be in alkaline or higher alkaline range
·It should be detergent compatible
· It should have specificity towards different proteins
Major detergent enzymes include proteases, amylases, lipases, cellulases, miscellaneous enzymes such as peroxidases and pullulanase. A recent trend is to reduce this phosphate content for environmental reasons. It may be replaced by sodium carbonate plus extra protease.
Proteases were introduced in the market in 1959 in the detergent Bio-40, produced by Schnyder Ltd in Switzerland. Most powder and liquid laundry detergents in the market, today, contain proteases. Proteases are of two types:
· Alkaline protease from Bacillus licheniformis, having optimum pH 8, for eg, liquid laundry product, (pH 7- 8.5), commercially known as Alcalase -Novonordisk Optimase- Genencor Inter
· High alkaline protease from Bacillus alkalophilus and Bacillus lentus, having an optimum pH 10. For eg, powder laundry products, automatic dish washing formulations, known by trade names of Savinase-Novo Nordisk, Purafet- Genencor Inter. Proteases enhance the cleaning of protein-based soils, such as grass and blood by catalyzing the breakdown of the constituent proteins in these soils through hydrolysis of the amide bonds between individual amino acids. In the case of serine endopeptidase, it contains a catalytic triad of amino acids at the active site;
· An aspartyl residue containing ß-COO¯
· A histidine containing the imidazole group
· A serine residue with p-OH as the functional group
The serine hydroxyl group functions as a potential nucleophile, where as both the aspartyl and histidine functional groups behave as general base catalysts facilitating the hydrolysis process.
The serine group initiates the nucleophilic attack on the peptide bond to form a tetrahedral intermediate, which undergoes an active hydrogen transfer, facilitated by both the histidine and aspartyl residues. The net effect of the addition of water across the bond generates the original protein. The protease hydrolysis involves the transfer of electrons between the amino acids at the active site and substrate. For proteases the three-dimensional arrangement of the catalytic triad is required for the enzyme to be active. Disturbances in the confirmation are likely to affect enzyme efficacy and therefore cleaning performance.
Limitations of proteases
· These were susceptible to oxygen bleaches and calcium sequestrates. But now, stable protease can be obtained
· Oxidative attack by peroxides or per acids on the methionine residue adjacent to the catalytic serine results in nearly 90% loss of enzyme activity. However, replacing methionine with oxidatively stable amino acids like alanine improves stability of enzyme towards oxygen bleach (Boguslawski et al, 1992)
· Protease substilisin requires at least one calcium ion, which maintains three- dimensional structure of enzyme. However, calcium- sequestering agents used in many laundry procedures to control water hardness can remove this calcium resulting in the decreased thermal and autolytic stability. This can be corrected by the introduction of negatively charged residues near the calcium-binding site, which increases the binding affinity of enzyme for calcium and results in improved stability towards calcium sequestrants (Krawczyk et at, 1997)
· Protease has limited applications towards the detergency of wool and Constituent silk, because of the proteinaceous nature of these fibres
· Proteases are added in an encapsulated or granulated form, which protects them from other detergent ingredient and eliminates the problem of autolysis or proteolysis of other enzymes. In aqueous detergent formulations, protease inhibitors show a preventive effect of avoiding contact of the protease molecules with each other as well as other enzyme molecules. This effect gets nullified on dilution and enzyme molecules are free to act on stains (Krawczyk et al, 1997)
Amylases facilitate the removal of starch-based food soils, by catalyzing the hydrolysis of glycosidic linkages in starch polymers. Generally, starch-containing stains are of chocolate, gravy, spaghetti, cocoa, pudding, etc. Amylases can be classified as:
a-amylases: These enzymes catalyze the hydrolysis of the amylose fractions of the starch under hydrolysis of the glycosidic bonds in the interior of the starch chain. The first step in the reaction is called as endoreaction & leads to oligosaccharides, where short chain water- soluble dextrins are produced.
ß-amylases: These enzymes acts on dextrins from reducing end and forms maltose units.
Amyloglycosidases: These enzymes act on the dextrin or maltose units and forms glucose units.
Pullulanases or isoamylases: These degrade starch directly into linear dextrins for they also attack ci-1, 6 glycosidic bonds.
a-amylases are mostly used for detergents, although recently other carbohydrate cleaving enzymes such as pullulanases or isoamylases have also been described for this application. a-amylases bring about the primary hydrolysis of starch into the oligosaccharides and dextrins. Currently, these enzymes are produced from bacteria. Bacillus subtilis. Bacillus amyloliquefaciens, and Bacillus licheniformis. These are available under the trade names Maxamyl- Genencor Int or Termamyl -Novo Nordisk.
Tomato-based sauces, butter, edible oils, chocolate and cosmetic stains are very difficult to remove as they form due to greasy food stains. Body soils, sebum and sweat on collars, cuffs and underarms, are generally composed of a mixture of proteins starch pigments and lipids. Lipases hydrolyze the water insoluble triglycerides components into the more water-soluble products as monoglycerides, diglycerides, free fatty acids and glycerol. The Novo Nordisk launched the first lipase product in 1987. They transferred the lipolase gene into the fungus Asper6yillus oryzae for industrial production, Genencor followed in 1993 with lumafast (Pseudomonas menocina) and Gist-Brocades in 1995 with Lupomax (Pseudomonas alcaligenes).
Currently, the known sources of lipases include mammalian lipases (human pancreases/colipases), fungal (Rhizomucor mehei, Humicola lanuginose, etc), yeast (Candida rugosa, Candida antartica), bacterial lipase (Pseudomonas glumae, Pseudomonas aeroginosa, Chrobacterium viscosum) (Ishida et al, 1995).
Lipases possess a catalytic triad that is similar to the serine proteases of trypsin and subtilisin type. Hence, these are also called as serine hydrolysate lysate. Lipases can decompose a fatty stain up to 25%, which then can be removed very easily because of the hydrophilic character (Dorrit et al, 1991). It is generally thought that lipases get adsorbed on to the hydrophobic stain during the washing period. And, during the drying cycle when the water content is decreased, the enzyme is activated and can hydrolyze triglycerides in the stain. This facilitates the removal of stain in the next wash cycle (Dorrit et al 1991). The enzyme also has stability over a broad range of temperature 30C to 60C. These novel alkaline lipases also retained 100% activity in the presence of strong oxidants.