Microbial a-amylases: a biotechnological perspective
Rani Gupta *,1, Paresh Gigras, Harapriya Mohapatra, Vineet Kumar Goswami, Bhavna Chauhan
Department of Microbiology, University of Delhi South Campus, Benito Juarez Marg, New Delhi 110 021, India Received 3 July 2002; accepted 30 January 2003
Abstract Amylasesare one of the most important and oldest industrial enzymes. These comprise hydrolases, which hydrolyse starch molecules to fine diverse products as dextrins, and progressively smaller polymers composed of glucose units. Large arrays of amylases are involved in the complete breakdown of starch. However, a-amylases which are the most in demand hydrolyse a-1,4 glycosidic bond in the interior of themolecule. a-Amylase holds the maximum market share of enzyme sales with its major application in the starch industry as well as its well-known usage in bakery. With the advent of new frontiers in biotechnology, the spectrum of a-amylase application has also expanded to medicinal and analytical chemistry as well as in automatic dishwashing detergents, textile desizing and the pulp and paper industry.Amylases are of ubiquitous occurrence, produced by plants, animals and microorganisms. However, microbial sources are the most preferred one for large scale production. Today a large number of microbial a-amylases are marketed with applications in different industrial sectors. This review focuses on the microbial amylases and their application with a biotechnological perspective. # 2003 ElsevierScience Ltd. All rights reserved.
Keywords: a-Amylase; Baking; Antistaling; Dextrinising activity; Starch liquefaction
1. Introduction Amylases are enzymes which hydrolyse starch molecules to give diverse products including dextrins and progressively smaller polymers composed of glucose units . These enzymes are of great significance in present day biotechnology with applications rangingfrom food, fermentation, textile to paper industries . Although amylases can be derived from several sources, including plants, animals and microorganisms, microbial enzymes generally meet industrial demands. Today a large number of microbial amylases are available commercially and they have almost completely replaced chemical hydrolysis of starch in starch processing industry . The history ofamylases began in 1811 when the first starch degrading enzyme was discovered by Kirchhoff.
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This was followed by several reports of digestive amylases and malt amylases. It was much later in 1930, that Ohlsson suggested theclassification of starch digestive enzymes in malt as a- and b-amylases according to the anomeric type of sugars produced by the enzyme reaction. a-Amylase (1,4-a-D-glucan-glucanhydrolase, EC. 18.104.22.168) is a widely distributed secretary enzyme. a-Amylases of different origin have been extensively studied. Amylases can be divided into two categories, endoamylases and exoamylases. Endoamylases catalysehydrolysis in a random manner in the interior of the starch molecule. This action causes the formation of linear and branched oligosaccharides of various chain lengths. Exoamylases hydrolyse from the non-reducing end, successively resulting in short end products. Today a large number of enzymes are known which hydrolyse starch molecule into different products and a combined action of various enzymes isrequired to hydrolyse starch completely. A number of reviews exist on amylases and their applications, however, none specifically covers a-amy-
0032-9592/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0032-9592(03)00053-0
R. Gupta et al. / Process Biochemistry 38 (2003) 1599 Á/1616
lases at length. a-Amylases are one of the most popular...