Alpha Amylases

 Amylase are enzymes that breakdown starch or glycogen. Amylases are produced by a variety of living organisms, ranging from bacteria to plants and humans. Microbial amylases are enzymes produced by microorganisms to hydrolyze starch. Bacteria and fungi secrete amylases to the outside of their cells to carryout extra cellular digestion. They were first produced in 1894 by the Japanese scientist Jokichi Takamine at Peoria, Illinois (USA) from a fungal source and was used as a pharmaceutical aid- Takadiastase (from A. oryzae) for the treatment of digestive disorders- a pharmaceutical digestive aid.

Starch is a polymer made of linear amylose D-glucose units joined by α -1,4-glycosidic bonds and branched amylopectin with α 1,6 -linkages at branching points. Amylases are important enzymes employed in processing industries for the hydrolysis of starch into simple sugars. 

 There are three types of amylases, namely: 

α amylase (endo-1,4-α-D glucohydrolase), β amylase (β-1,4-glucan maltohydrolase), and glucoamylase (amyloglucosidase). Each of the three types of amylases has a unique way of acting on starch substrate. 

Starch <α-amylase>  dextrins + maltose (liquefying amylase) 

Starch <β-amylase > maltose (saccharifying amylase) 

Dextrins <dextrinase> maltose 

Starch or dextrins glucose 

 α amylase (being an endoamylase) cleaves or breaks the α-1,4-glucosidic linkages in starch internally to give glucose, maltose, or dextrins.

β amylase, an exoamylase, cleaves the glycolytic bonds removing two glucose units at a time thus producing maltose. Glucoamylase, on the other hand, cleaves both the α-1,4 and α-1,6-glucosidic linkages to yield glucose, maltose, and limit dextrins. β-Amylase, is a saccharifying enzyme, forming maltose directly from starch by cleaving disaccharide units from the open ends of chains. The a-amylases have good liquefying ability. 

Amyloglucosidase is a saccharifying enzyme unique in that it attacks starch and 1,4-linked glucose oligosaccharides with direct formation of glucose. A range of amylases, suitable for almost any kind or extent of starch conversion, is now available from microbial sources. Microbial amylases can be produced by bacteria and fungi (which include molds and yeast). Fungi among many microbes are good sources of amylolytic enzymes. Amongst the bacteria genera, the genus Bacillus (especially Bacillus subtilis, Bacillus licheniformis, and Bacillus amyloliquefaciens) are greatly used for amylase production. However, amongst the fungi, Aspergillus spp and Rhizopus spp are the preferred strains for amylase production. 

 Although amylases can be produced by plants, animals, and microorganisms, microbial amylases are important because of their greater thermal stability, different sugar profiles, and a long history of safe use. 

Application of Microbial Amylases

Microbial amylases (especially thermostable alpha amylase) have various industrial applications because of their greater thermal stability, different sugar profiles, and a long history of safe use. 

 They can be exploited for high fructose corn preparation, for the production of alcohol and brewing, for paper coating, for the preparation of detergents. Industries requiring microbial amylases include: clinical, medicinal, analytical chemistry, textile, food, and distilling industries. 

Microbial amylases are used for modifying starch in vegetable purees, and in treating vegetables for canning. Other applications of microbial amylases where both fungal and bacterial enzymes are utilized are in processing cereal products for food dextrin and sugar mixtures and for breakfast foods, for preparation of chocolate and licorice syrups to keep them from congealing, and for recovering sugars from scrap candy of high starch content. Fungal amylases are also used for starch removal for flavoring extracts and for fruit extracts and juices, and in preparing clear, starch-free pectin. By proper control of the type and proportion of enzymes used (α -amylase, amyloglucosidase, maltase), syrups of any desired proportions of glucose, maltose, and dextrins may be produced.