Characterization of an α‐amylase from sorghum (Sorghum bicolor) obtained under optimized conditions

Sorghum malt α‐amylase can compete with bacterial α‐amylase in industrial applications, if sufficiently stable and produced in a large enough quantity. Conditions for maximal α‐amylase production in sorghum malt and the physico‐chemical properties of the α‐amylase so produced are reported in this study. Sorghum grains were steeped in buffers with varying pH (4.0–8.0) for 24 h, at room temperature, and germinated for another 48 h to obtain the green malt. The buffer that induced the highest quantity of α‐amylase was chosen as the optimal pH and served as the medium for further steeping experiments conducted at different temperatures (10, 20, 30, 40, 50 and 60°C). The α‐amylase activity in the extract was determined in order to obtain the optimum temperature for α‐amylase induction at this particular pH. For the purpose of comparison, the α‐amylase produced at the optimum pH and temperature was purified to apparent homogeneity by a combination of ion‐exchange and size‐exclusion chromatography, and further characterized. Eight‐fold higher α‐amylase activity was induced in pH 6.5 buffer at 20°C compared with water, the traditional steeping medium. The K_m and V_max were estimated to be 1.092 ± 0.05 mg mL^?1 and 3516 ± 1.981 units min^?1, respectively. The activation energy of the purified amylase for starch hydrolysis was 6.2 kcal K^?1 mol^?1. Chlorides of calcium and manganese served as good activators, whereas CuSO₄ inhibited the enzyme with a 42% loss in activity at 312 mm salt concentration. Copyright © 2012 The Institute of Brewing & Distilling