Isolation of raw starch hydrolysing fungi and purification of α-amylase from Geotrichum candidum CMSS06

Three starch degrading fungal species were isolated by exposing raw cassava and potato substrates to air and soil solutions. These three fungi were identified as Aspergillus spp., Mucor spp. and Geotrichum candidum by slide culture method. The optimum culture conditions for the production of extra- cellular α-amylase from these three species were determined by measuring the α-amylase activity, protein content and the pH of the culture media at 12 h intervals.

The highest raw starch hydrolysing α-amylase activity (6540 mU/mL) was shown by the species G.candidum 72 h after incubation. The culture supernatant containing the enzyme activity was concentrated by 50% ammonium sulphate precipitation and two peaks were identified to contain the high α-amylase activity following Dowex-cation exchange column chromatography. The two fractions collected from these two activity peaks had the specific activity of 136.3 mU/mL and 394.7 mU/ml for hydrolysing raw starch (RSHI) and soluble starch (SSI) respectively. The purification fold and recovery of the enzyme were 3.5 and 2 in RSHI and 11.2 and 10.9 in SSI. Further the maximum activity of the enzyme in RSHI fraction was detected at 40 º C and pH 7.

Keywords: Cassava, fungi, Geotrichum candidum, raw starch, α-amylase

doi :10.4038/jnsfsr.v37i2.1064

J.Natn.Sci.Foundation Sri Lanka 2009 37 (2):93-98