β-galactosidase from <em>Lactobacillus delbrueckii </em>and <em>Lactobacillus </em><em>reuteri</em>: Optimization, characterization and formation of galactooligosaccharides

Abstract

Beta-galactosidase (β-gal) is one of the important commercial enzymes having several applications in food, pharmaceutical industry and in the synthesis of galactooligosaccharides known for their prebiotic properties. The production of β-gal from <em>Lactobacillus delbrueckii </em>and <em>Lactobacillus reuteri</em> was studied. The highest yield of β-gal was achieved using wheat flour as carbon source. Beef extract gave the highest value of enzymatic production by <em>L. delbrueckii</em> reached 24.25 U/ml, while <em>L. reuteri</em> produced the highest β-gal (20.20 U/ml) in the presence of peptone. The optimum β-gal activity was recorded on 15 mM O-nitrophenyl β-D-galactopyranoside (ONPG) at 40^oC and pH 7. Further enzyme activity was enhanced in the presence of Mg²⁺, Mn²⁺and Fe²⁺, while it was decreased by Ag⁺ and Ni⁺ for both strains. The production of galactooligosaccharides (GalOS) from lactose using the produced β-gal was investigated. The maximum yield of 40 and 35% (w/w) GalOS could be achieved with β-gal of <em>L. delbrueckii </em>and <em>L. </em><em>reuteri</em>, respectively from 40% lactose solution at 40°C and pH 7. These characteristics of produced β-gal showed that it could be a promising candidate for various industrial as well as biotechnological applications.