THESIS
THESIS
THESIS
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70 -80 o C for α-amylases of bacteria origin (Bacillus stearothermophilus, Bacillus<br />
subtilis, and B. licheniformis).<br />
Action pattern of the α-amylases: These endoenzymes<br />
hydrolyze α-(1,4) linkages on several chains and in several places along the same<br />
chain, releasing glucose and oligosaccharides of two to seven glucosyl units with an<br />
α-anomeric reducing end (Figure 11). Their action rapidly reduces the viscosity of<br />
starch solutions, hence the occasional use of the term liquefying amylases to describe<br />
them. The action pattern of α-amylases is a function of its origin and of the nature of<br />
the substrate (Buisson et al. 1987).<br />
For amylose, at the end products are essentially maltose and<br />
maltotriose. Hydrolysis of maltotriose into maltose and glucose occurs later, since this<br />
oligosaccharide is more resistant to hydrolysis. For an amylose chain in solution, it<br />
random coil conformation favors the breakage of internal bonds close to one of the<br />
ends. As a result, the attack, however repetitive, generates chains with a high degree<br />
of polymerization, leaving the analysis of experimental results much more complex.<br />
For amylopectin, persistent branched limit dextrins remain, along with the above-<br />
mentioned oligosaccharides, glucose, maltose and maltoriose. These limit α- dextrins<br />
contain all α-(1,6) linkages from the original macromolecule and adjacent α-(1,4)<br />
linkages with a heightened resistance to enzymatic hydrolysis. Depending on the<br />
origin of the α-amylase, the limit α-dextrins may contain three (B. subtilis), four<br />
(pancreas and A. oryzae), or five glucosy units (barley malt)( Hayashida et al. 1990).<br />
2) Exoenzymes<br />
The exoenzymes are chiefly represented by the β- amylase group<br />
(E.C. 3.2.1.2), although new microbial exoenzymes that produce one specific type of<br />
oligosaccharide have been recently discovered. These different enzymes are<br />
distinguished essentially by the type of hydrolysis product generated that is, maltose,<br />
maltotriose, maltoterose, maltopentose, or maltohexose (Abe et al.1988).<br />
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