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 CuSO 4 inhibited the enzyme with a 42% loss in activity at 312 m m salt concentration. Copyright © 2012 The Institute of Brewing & Distilling