PURIFICATION AND PARTIAL CHARACTERIZATION OF A RAW STARCH- DIGESTING AMYLASE FROM ASPERGILLUS TAMARII

AUTHOR: ONU CLEMENT OKAFOR

DEPARTMENT: APPLIED MICROBIOLOGY AND BREWING

AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA

A raw starch-digesting amylase (RSDA) and a glucoamylase from Aspergillus tamarii were produced in submerged culture with soluble starch as carbon source. The enzymes were purified from culture supernatant fluid by 4M sucrose concentration, ion exchange chromatography on S–andQ-Sepharose (Fast flow), respectively and hydrophobic interaction chromatography. The overall yield of the purified amylase was 25.47% with a specific activity of 3.63μmg-1 while that of the glucoamylase was 25.75% with a specific activity of 3.47umg-1 . Optimum temperature for both enzymes was 600C and both enzymes tolerated wide temperature range (300C – 800C) for 20 minutes at pH 6.0 – 8.0 in 0.1M citrate phosphate buffer. However, the RSDA activity appears to be stable over a relatively broad pH range (5.0 – 9.0) suggesting acid and alkali tolerance when acting on raw starch. Same for the glucoamylase. The activities of both enzymes were enhanced by Mn2+ , Co2+ , and Fe2+ while Ba2+ , Ag2+ and, Hg2+ had strong inhibitory effects on the activity of both enzymes. The RSDA hydrolyzed amylose more substantially relative to pullulan, amylopectin, soluble starch, inulin and dextran. Glucose was the end product of RSDA hydrolysis while maltose, maltotetraose and glucose were the end products of glucoamylase hydrolysis.

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