Amylases sources

Immobilized cellulase and amylase are able to hydrolyze cellulose and starch. However, the immobilized enzymes possess only about 1-6% of the activity of the soluble forms. In addition, immobilization clearly enhanced the thermal stability of amylase. Immobilized amylase retained more than half of its activity, even after incubation at 125°C. By comparison, soluble amylase was almost completely inactivated under these conditions. Furthermore, kinetics modeling indicates that the susceptibility to product inhibition is dependent on the amylase source. Finally, immobilization can reduce the susceptibility to product inhibition fQ was less for each of the immobilized forms, compared with their soluble counterparts. 

Diastase or amylase is formed when malt is produced by the germination of barley grains. Malt is therefore a good source of the enzyme. Diastase is also secreted by the salivary glands (when it is known as ptyalin), and also by the pancreas. Its function is to hydrolysef starch to a mixture of maltose and dextrin ... 

After 30 hours, the maximum and critical fermentation is underway and the pH must remain above 4.0 for optimal fermentation. However, accompanying bacterial contamination from various sources such as yeast contamination, improper cleaning procedures, slow yeast growth, or excessive temperatures can result in a pH below 4.0. The remaining amylase enzymes, referred to as secondary conversion agents, are inactivated and can no longer convert the dextrins to maltose. Under these circumstances, the fermentor pH continues to drop because of acid production of the bacteria, and the pH can drop to as low as 3.0. The obvious result is a low ethanol yield and quaUty deterioration. 

The mode of action of a-amylases depends on the source from which the enzyme was isolated and on the substrate, and the data available present a bewildering array of facts difficult to correlate. 

Malt Flour. Malt flour is the traditional source of extra a-amylase to add to flour. Now that British bread flour is substantially home grown there is little need of this supplementation. Some bakers would claim that malt flour improves the flavour of the bread. Malt flour is a food and not an additive. 

The second source of biochemicals is molecules excreted from cells such as extracellular enzymes and other organic matter. A typical example is cellulase, which is excreted by fungi such as Penicillium in order to break down wood and woody material into sugars that can be used by the organisms. Other common extracellular enzymes found in soil are ureases and amylases. Often enzymes are associated with clay particles, and in such associations, their activity may be increased, decreased, unchanged, or completely destroyed [15],... 

If amylases are to be used as tools for the detailed study of the breakdown and structure of their substrates it is obviously important to separate them from other enzymes and from other naturally associated constituents which may influence the results. It is then equally important to study the properties of the purified amylase and to supply it with the chemical environment necessary to protect it from inactivation and to enable it to act efficiently. With beta amylases this ideal has often been approached. Beta amylases from several sources have been prepared by selective inactivation of other enzymes that accompany them in nature23 and highly active products have been obtained by extensive purification.20 24-26 Balls and his associates have recently reported the crystallization of beta amylase from sweet potato.27... 

While alpha amylases from many sources are known, the present discussion will deal mainly with the alpha amylase of malted barley, pancreatic amylase and the amylase of Aspergillus oryzae. These... 

Although the mechanism of the hydrolysis of starch by beta amylase has been well established, the hydrolysis of starch by the alpha amylases has proven much more complicated. The data already available show that alpha amylases from different sources hydrolyze starches very differently and that these differences are more marked in the early than in the late stages of the hydrolysis of starch. Unfortunately, sufficient strictly comparable data are not available at present to make possible clear cut statements as to the similarities and differences in the mode of action of the three amylases discussed here. However, it is evident that further work with these and other amylases will be amply repaid as it adds to our exact information and increases our understanding of these important catalysts and of the substrates upon which they act. 

Enzymes that perform the same catalytic function are known as homologous enzymes and fall into two classes. Heteroenzymes are derived from different sources and although they catalyse the same reaction they show different physical and kinetic characteristics. The hydrolytic enzyme a-amylase (EC 3.2.1.1) is found in the pancreatic secretion in man and is different from the enzymes of the same name which are derived from bacteria or malt. Iso-enzymes, sometimes referred to as isozymes, are different molecular forms of the same enzyme and are found in the same animal or organism although they often show a pattern of distribution between tissues. 

The greatest variety of industrial enzymes are presently derived from microbial sources, with a lesser diversity coming from plant and animal sources 34), Enzymes derived from plant sources and which are used extensively in the food industry include papain, bromelain, ficin, and amylases. Animal enzymes of economic importance include trypsins, lipases, and gastric proteases. 

The production of ethanol from cooked rice starch (Moebus and Teuber, 1985) differs from the normal process of spraying the carbon source into the bed since all of the carbon source is made available at the start of the run, subject only to the breakdown of starch to glucose (and maltose) by amylases. The starch (0.3 mm particles), amylases and yeast pellets were mixed in the bed and water sprayed in to maintain the fermentative activity of the yeast. The fermentation was carried out at 31.5°C. 

Starch derived from maize, potatoes, barley, cassava or other somces must be pretreated with hydrolytic enzymes (amylases, amyloglucosidase, proteases), which carry out liquefaction, saccharification and protein hydrolysis, respectively, before it can be fermented by yeasts and other microorganisms into potable or non-potable alcohol. Enzymes can be added in the form of malt (germinated barley) or koji (germinated rice), but this is expensive. Therefore, industrial enzymes have nearly totally replaced malt and koji as enzyme sources, thereby not only improving the economics but also the predictability of the process. 

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