Comparative studies on α-amylases from malted maize (Zea mays), millet (Eleusine coracana) and Sorghum (Sorghum bicolor)

Starch-digesting enzymes were extracted from unmalted, malted, malted and kilned samples of maize (Zea mays), millet (Eleusine coracana) and sorghum (Sorghum bicolor) and the specific activities were determined with soluble starch as substrate. The extract of malted and kilned samples was partially purified by using ammonium sulphate fractionation and the kinetic parameters of the α-amylases were determined using starch as substrate. The heat stability of the enzymes at different temperatures was also established. The results showed that all the malted grains expressed α-amylases in appreciable quantity. Sorghum had the lowest drop in α-amylases activity after kilning. Sorghum α-amylases also had the lowest Km for starch, and maize, the highest. Amylases from maize were least stable to heat denaturation at all temperatures investigated, while sorghum and millet α-amylases had similar sensitivity to heat inactivation, although sorghum amylases were slightly more resistant. The overall summary showed that α-amylases from maize were least stable to heat denaturation, and also had the lowest affinity for soluble starch. A combination of these factors might have influenced the choice of sorghum grains over maize and millet for commercial malt production.