Microbial amylases and their industrial applications
Amylases play a fundamental role in carbohydrate metabolism of microorganisms, plants and higher organisms. Microbial amylases are starch degrading enzymes derived from microorganism which catalyse the hydrolysis of polysaccharides into sugars and are grouped into three classes: alpha-amylases, beta-amylases and glucoamylases. Microbial amylases can be used for a wide range of purposes, however the most popular use of these enzymes are found in textile seizing, starch, brewing, distilling, and in the pulp and paper industry. Today a large number of microbial amylases are marketed with applications in different industrial sectors. Recent studies have been targeted towards the protein engineering of amylases in order to enhance production, thermostability, selectivity, optimum pH and improve catalytic activity.
Microbial amylases derived from fungal and bacterial sources are becoming popular in a number of industries. In terms of the baking industry, amylases isolated from Bacillus subtilis SUH 4-2, and Streptomyces albus KSM-35 have been shown to significantly reduce bread staling rate during 7 days of storage, showing great potential as an antistaling agent for bread. A recent trend has been to use intermediate temperature stable (ITS) alpha-amylases which become inactive much before the completion of the baking process, avoiding stickiness in bread. Studies contributing to the textile industry have shown that mixed amylases obtained from A.niger and A.flavus exhibit higher desizing efficiency of grey cotton fabrics and could serve as a better alternative for the existing range of desizing agents. In regards to the starch industry, microorganisms such as Bacillusstearothermophilus have been employed for liquefaction of starch into soluble, short-chain dextrins, which is then used for the production of high glucose syrups.
Despite the use of microbial amylases in a wide range of industries, there is an underlying need for production improvement. Natural bacterial and fungal strains are limited by their genetic and physiological properties and therefore have a maximum capacity for synthesis and secretion of extracellular enzymes. Therefore to combat this problem, genetic recombination can be used. Target-directed screening and genetic recombination has led to an improvement of alpha-amylase production and export in B.licheniformis.
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