الفهرس 
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Abstract
During the last 10 years, galacto-oligosaccharides (GOS) were reported to be beneficial for human health, and they are now recognized as prebiotics. GOS, nondigestible oligosaccharides, are not hydrolyzed or absorbed in the upper intestinal tract; they pass on the colon where they are fermented selectively by beneficial intestinal bacteria. Besides the prebiotic effects, these GOS have low cariogenecity, low caloric values and low sweetness (Maischberger et al., 2008; Sako et al., 1999). β-Galactosidase based medical and industrial applications include cleavage of blood types A and B, biosensor for specific lactose determination in milk and disease diagnosis, treatment of lactose malabsorption, production of lactose hydrolyzed milk (Asraf and Gunasekaran, 2010). These enzymes catalyze the hydrolysis of lactose into glucose and galactose and transgalactosylation reactions with lactose as acceptor of galactose units giving rise to galacto-oligosaccharides of different glycosidic linkages and molecular weights (Otieno, 2010; Hernández-Hernández et al., 2011).
The enzyme β-galactosidase occurs widely in nature and has been isolated from animal and plant sources as well as microorganism. However, compared with animal and plant sources, the microbial is produced at higher yield and is more technologically important (Grosova et al., 2008).
The aim of the present study is to investigate the effect of components of fermentation medium on the production of β-galactosidase produced by some organisms. Fungal cells were immobilized and different medium composition also investigated.The β-galactosidase was partially purified and characterized to determine their molecular mass using SDS-PAGE techniques. The β-galactosidase of the crude and pure enzyme was also investigated.