A new strain of Bacillus sp. I-5 isolated from natural soil samples, showed a high digesting activity towards different types of raw starches including potato, wheat, maize, and rice. Upon optimization of various environmental and cultural conditions employing solid state fermentation of wheat bran, the a-amylase yield of 825 mg^-1 dry substrate was achieved. The kinetic characterization of the enzyme exhibited the maximum activity at 65 ^oC and revealed a high thermostability in the presence of 10 mM CaCl₂.2H₂O where it could retain more than 80% residual activity at 80 ^oC after 2½ h. At 90 ^oC and 100 ^oC, the enzyme retained 48% and 52% of its maximum activity after 1 and ½ h respectively. The enzyme preparation had a strong affinity towards various raw starch granules and was almost completely adsorbed. It also hydrolyzed these starches at a concentration of 12.5% significantly with highest digestion of potato starch followed by wheat starch.

Raw starch is the most abundant storage polysaccharide of glucose in the world (Shiau et al., 2003) and is the basic source of chemical energy for life sustenance, whose worldwide production, rated at 2×10¹⁰ tons year^-1 corresponds to a large fraction of total food production (Sarikaya et al., 2000). Thus, it constitutes an inexpensive source for production of syrups containing glucose, fructose or maltose, which are widely used in food industries (Roy and Gupta, 2004). In addition to that, the sugars produced can be fermented to produce bioethanol (Giordano et al., 2000). The main sources of starch are rice, wheat and maize among the grain crops and potato, yam, and cassava among the tuber crops. Most of the starch is used for beverage preparation after hydrolysis with amylase and other amylolytic enzymes (Pacheco Chavez et al., 2004).

An Efficient Hydrolysis of Raw Starches by a Thermostable Bacterial a-amylase from Solid-state Cultures of Bacillus sp. I-5, activity, starch, potato, production, enzyme, glucose, bioethanol, CaClHO, characterization, Chavez, chemical, concentration, corresponds, digestion, environmental, energy, enzymes, fermented, fructose, hydrolyzed, kinetic, isolated, optimization, Pacheco, polysaccharide