α-Amylase production by thermophilic Bacillus sp strain SMIA-2 cultivated in liquid cultures containing soluble starch as a carbon source and supplemented with 0.05% whey protein and 0.2% peptone reached a maximum activity at 32 h, with levels of 37 U/mL. Studies on the amylase characterization revealed that the optimum temperature of this enzyme was 90ºC. The enzyme was stable for 1 h at temperatures ranging from 40-50ºC while at 90ºC, 66% of its maximum activity was lost. However, in the presence of 5 mM CaCl2, the enzyme was stable at 90ºC for 30 min and retained about 58% residual activity after 1 h. The optimum pH of the enzyme was found to be 8.5. After incubation of enzyme for 2 h at pH 9.5 and 11.0 was observed a decrease of about 6.3% and 16.5% of its original activity. At pH 6.0 the enzyme lost about 36% of its original activity. . In the presence of 2.0 M NaCl, 63% of amylase activity was retained after 2 h incubation at 45ºC. The amylase exhibited more than 70% activity when incubated for 1 h at 50ºC with sodium dodecyl sulphate. However, very little residual activity was obtained with sodium hypochlorite and with hydrogen peroxide the enzyme was completely inhibited. The compatibility of Bacillus sp SMIA-2 amylase with certain commercial detergents was shown to be good as the enzyme retained 86%, 85% and 75% of its activity after 20 min incubation at 50ºC in the presence of the detergent brands Omo ® , Campeiro ® and Tide ® , respectively.

As amilases constituem um dos mais importantes grupos de enzimas industriais com aplicações em diferentes indústrias como de alimentos, têxtil, química, farmacêutica e de detergentes (DEMIRKAN et al., 2005;GUPTA et al., 2003;BORCHERT, 2000;PANDEY et al., 2005;SOCCOL, 2005;SURMELY, 2003).As enzimas amilolíticas são responsáveis por 25 a 33% da produção mundial de enzimas, ocupando segundo lugar logo após as proteases (NGUYEN et al., 2002). Dentre estas, a mais importante é a α-amilase, pois desempenha um papel fundamental na conversão do amido em produtos de baixo peso molecular, que podem ser utilizados por outras enzimas do AbstractThe optimization of culture conditions for the production of α-amylase by the thermophilic Bacillus sp strain SMIA-2 was carried out. In addition, the enzymatic hydrolysis of starch from several sources, such as potato, cassava and corn was investigated. Alpha-amylase production by Bacillus sp SMIA-2 cultivated in liquid cultures containing starch as carbon source and supplemented with 0.5 g.L -1 whey protein and 2.0 g.L -1 peptone reached a maximum of 37 U.mL -1 at 32 hours. The microorganism was capable of utilizing several carbon sources, but amylase activity varied with each source. Starch was the best carbon source for amylase secretion, while lactose, maltose, sucrose, galactose, and glucose were not very effective. Decreasing starch concentration in the medium to 2.5 g.L -1 improved organism growth and enzyme activity. At higher starch concentrations, enzyme production was comparatively lower. Among the various organic and inorganic nitrogen sources, peptone (2.0 g.L -1 ) was found to be the best. Regarding the amount of whey protein in the medium, the concentration of 0.25 g.L -1 was considered the most effective for amylase secretion by the organism. Maximum amylase activity was observed at 50 °C and pH 8.5. The enzyme was able to degrade all the starches tested. Potato starch hydrolysis resulted in a higher yield of reducing sugars in comparison to the other starches. Soluble and cassava starch were, respectively, in second and third positions regarding the liberation of reducing sugars, while the amylase studied showed a slightly lower affinity for corn starch. Increasing the reaction temperature to 70 °C resulted in higher levels of reducing sugars after the hydrolysis of the substrates, except for soluble starch. Keywords: amylase; Bacillus; starch; hydrolysis; thermophilic bacterium. ResumoA otimização das condições de cultivo para a produção de α-amilase por um termofílico Bacillus sp. cepa SMIA-2 foi realizada. Além disso, a hidrólise enzimática do amido, proveniente de várias fontes tais como batata, mandioca e milho, foi também investigada. A produção de α-amilase por Bacillus sp. SMIA-2, cultivado em meio líquido contendo amido (5 g.L -1 ) como fonte de carbono e suplementado com 0,5 g.L -1 de proteínas do soro de leite e 2 g.L -1 de peptona, alcançou o máximo em 32 horas com níveis de 37 U.mL -1 . O microrganismo foi capaz de utilizar diversas fontes de carbono, p...