期刊
PROCESS BIOCHEMISTRY
卷 39, 期 11, 页码 1723-1729出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.procbio.2003.07.008
关键词
thermostable alpha-galactosidase; Bacillus stearothermophilus; soybeans; soymilk hydrolysis; oligo-saccharides; flatulence
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.
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