Hydrolysis of maize starch using amylolytic enzymes extracted from sorghum malt
Amylases, a-amylase (EC 126.96.36.199, α-1, 4-glucan-4-glucanohydrolase) and glucoamylase (EC 188.8.131.52, α-1, 4; α-1, 6-glucan glucohydrolase; amyloglucosidase), extracted and partially purified from sorghum malt
were used to hydrolyze maize starch. The process and products of the enzymatic hydrolysis were also compared with that of acid hydrolysis using hydrochloric acid. Maize grains were dry milled into flour as starch used for the hydrolytic procedures. Green (for glucoamylase) and dry (for a-amylase) sorghum malts were homogenized and the amylases were extracted in appropriate buffer solutions, precipitated by ammonium sulphate and desalted by column chromatography. Acid hydrolysis was investigated under various temperature, acid concentrations and starch concentrations. The combination of acid–enzyme hydrolyses involved the use of 0.1 M HCl followed by the addition of the extracted a-amylase and glucoamylase and enzyme-enzyme (a- amylase and glucoamylase) hydrolyses were also investigated. The results of the acid hydrolysis showed that the concentration of reducing sugar produced increased with temperature of hydrolysis and the concentrations of the acid. However, the products decreased with increasing starch granule concentration. The overall study showed that enzyme–enzyme hydrolysis has the highest dextrose equivalent of 47.0% followed by acid– enzyme with 43.0% and the acid hydrolysis with 27.0%.
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Keywords: a-amylase, glucoamylase, maize (Zea may), Sorghum bicolor (Sorghum).