Saturday, 26 January 2013
Enzyme (Cellulase ) Production
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.