Sunday, 27 January 2013
Proteases in leather Industry
Proteases belong to a group of proteolytic enzymes. They are obtained by microbial fermentations and are meant to use in leather industry for Dehairing, bating and soaking purposes. Their major use is in detergent industry too where they are used for breaking proteinaceous matter caused by body secretions, food stuffs and blood stains. These enzymes are obtained from plants, animals and microbial sources. Animal and Microbial Proteases from Fungi and bacteria re used in the pretanning processes of leather manufacture.
Animal Proteases are mixture of Trypsin, Chymotrypsin and various Peptidases which may contain amylase or lipase as secondary enzymes.
Proteases differ in their pH range as follows:
Acid Proteases: pH 2.5 – 6.0 derived from A. satoi
Alkaline Proteases: belong to group of serine proteases. More heat sensitive and heat
deactivate at 600 C
Neutral Proteases: Obtained from Aspergillus and Penicillium spp.
Enzymes in Dehairing
Dehairing involves the digestion of basal cells of hair bulb and cells of malphigian layer. This is followed by loosening of hair with an attack on outermost sheath and breakdown of inner root sheath and parts of hair that are not keratinized.
Various Enzymes used in dehairing process are:
CLARIZYME: has been developed especially for dehairing of skins and hides. It is an alkaline protease derived from A. Flavus. It grows rapidly on wheat bran and produce large amount of protease.
Enzymes from bacteria have gained much importance because of commercial interest , easy production, high yield and easy recovery of enzyme. Examples are, Bacillus and Streptomyces spp.
Keratinases: hydrolyse Keratins are obtained from S. fradiae.
Enzymes in Soaking:
Soaking is the first operation where in hides and skins are cleaned and softened with water. Soaking is necessary for solubilisation and elimination of salts and globulin proteins contained within fibrous structures of hides and skins. It is carried out at alkaline conditions at temperature of 10-200C.
Advantages of soaking are production of leather with less wrinkled skin.
Alkaline Proteases of Bacterial & Fungal origin has been used for soaking which reduces the need of chemicals.
Enzymes in Bating:
Bating is a process in which hides are softened by treating them in warm infusion of animal dung and product used for such purposes is called as BATE. Main objective of bating is to remove proteinaceous materials like albumin, globulins, mucoids from hides and skin and allow splitting up of collagen fibres to facilitate penetration of tanning materials and other chemicals, thereby giving finished leather with desired properties like feel, softness and pliability etc. Principal materials which a bate contains are proteolytic enzyme, a carrier for enzyme, wood flour and deliming agent like Ammonium chloride.
Enzymes from Aspergillus spp. are used in bating.
A combination of both mold and pancreatic enzymes are ideal bates.
Enzymes in Degreasing:
Degreasing is an essential step for production of glove and clothing leather. This process involves removal of excess natural fats from greasy skin. This grease results in defects like uneven dyeing, finishing and staining. Degreasing helps to obtain soft and pliable;e leather for garment manufacture.
It is carried out using aqueous emulsification with detergents or by solvent extraction since solvents are hazardous. So Lipase is used as an alternative for various solvents.
Acid Lipase from Rhizopus has been very effective in degreasing of sheep skins.
Fungal Lipase from A. Niger is also a good degreasing agent.
Alkaline Bacterial Lipase at pH of 9-9.4 is good for degreasing pig skin.
Saturday, 26 January 2013
Cellulase term is referred to all enzymes which cleave beta, 1-4 glycosidic linkages in cellulose. Many bacteria and fungi are celluloytic but preparations marketed for industrial applications are derived from Aspegillus niger, Neurospora and Trichoderma viridae. Aspergillus enzyme exerts good activity on CMC (carboxy methyl cellulose) but fails to attack on solid cellulose because it lacks a important component i.e. C1 Cellulase. Cellulase is multienzyme complex with 2 important components called C1 and Cx. Both have important functions.
C1 can attack upon native cellulose of higher crystallinity while Cx cannot attack such kind of cellulose but can split in turn the cellulose fragments which have been derived by action of C1.
Trichoderma produces an enzyme complex with high levels of C1 cellulase which extensively degrades insoluble cellulose.
Cultivation & Purification
In large scale fermentation A. niger is mostly cultured by wheat bran tray method. This process yields high levels of enzyme. Extraction of cellulose from solid substrate cultures is performed by percolation of dried mold bran with 0.02 to 0.1 M lactic acid.
Neurospora and Trichoderma are grown by submerged culture. For continuous culture it is advantageous that T. Viride produces a suspension of short mycelia threads, rarely forming pellets. For submerged cultivations bran and wheat straw pre-treated with alkali can be used as a source of cellulose. Ammonium ions can be used a suitable nitrogen source. A correct pH profile is necessary to give optimum enzyme yields in batch culture concentration and purification of enzyme is carried out by precipitation, adsorption and gel filtration techniques.
Ammonium sulphate is used for precipitation followed by centrifugation at 10,000 g for 10 minutes. After separating the sediment supernatant is subjected to re centrifugation for 10,000 g for 10 minutes. Precipitates are suspended in 0.5 M acetate buffer with pH 5 and crystallisation procedures are followed.
Ø Cellulase is currently used to improve texture and palatability of poor quality vegetables.
Ø It also accelerates drying of vegetables.
Ø A potential use of cellulose is conversion of cellulosic material to glucose and other sugars which in turn can be used as microbial substrates in variety of fermentations e.g. Alcohol.