THESIS

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