Characterization of an<i>α</i>-amylase from sorghum (<i>Sorghum bicolor</i>) obtained under optimized conditions

Abstract

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 Km and Vmax 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