Thermostable α-galactosidase from Bacillus stearothermophilus (NCIM 5146) and its application in the removal of flatulence causing factors from soymilk

Thermostable, neutral, extracellular alpha-galactosidase with wide pH stability was produced by a newly isolated strain of Bacillus stearothermophilus (NCIM 5146) grown on cheap agricultural residues at 60 degreesC, under submerged fermentation conditions. The maximum alpha-galactosidase activity (2.0 U/ml) was found when soybean meal was used as a carbon source along with yeast extract and ammonium sulphate as a nitrogen source. The pH optimum of alpha-galactosidase was 6.5-7.0 and the enzyme was stable in the pH range of 3-10. The enzyme exhibited an optimum temperature of 65 degreesC. The half-life of the enzyme at 70 degreesC was 80 min. The enzyme was active against synthetic as well as natural substrates. The K-m values determined for pNPG, stachyose, raffinose and melibiose were 0.625, 3.33, 6.66 and 13.33 mM, respectively. The V-max values were 4.3 x 10(7), 18.03, 12.65 and 6.3 x 10(3) mumol/min mg, respectively, for the above substrates. Enzyme activity was strongly inhibited by Ag+, Hg2+ and Cu2+ metal salts. No significant inhibition was found in the presence of different sugars. The enzyme hydrolyzes flatulence causing galacto-oligosaccharides, viz. raffinose and stachyose present in the soymilk at 65 degreesC within 2 h of treatment, suggesting its potential application in soymilk and related food industry. (C) 2003 Elsevier Ltd. All rights reserved.