SYNTHESIS OF LACTITOL-DERIVED OLIGOSACCHARIDES BY DIFFERENT MICROBIAL β-GALACTOSIDASES.

ZÁRATE G.; FARA, A.; MONTILLA, A.

Mendoza

Congreso; LVI SAIB Meeting ? XV SAMIGE Meeting; 2020

SAIB-SAMIGE

Galactooligosaccharies (GOS) are non-digestible prebiotic compounds that can be synthesized by β-galactosidase (β-gal) enzyme from different microbial sources. Lactic acid bacteria (LAB) and propionibacteria (PAB) have been extensively studied because of their safe status (GRAS of FDA and QPS of EFSA) that allow the use of their enzymes without extensive purification in food-related applications. β-gal catalyzes transgalactosylation reactions from lactose or its derivatives. Lactitol is a polyol generally used as sweetener that is not found in nature. It is chemically produced by the catalytic hydrogenation of lactose. In this work, the synthesis of oligosaccharides derived from lactitol by cell-free extracts (CFE) of Lactobacillus bulgaricus CRL 450 and Propionibacterium acidipropionici LET 120 was assessed and compared with commercial enzymes such us Lactozym (Kluyveromyces lactis β -gal), Biolactasa (Bacillus circulans β -gal) and Aspergillus oryzae β -gal. Transglycosylation reactions were carried out with 10 U/mg of β-gal in 0.05M sodium phosphate buffer, pH 7, containing 0.005M MgCl2 and lactitol at a concentration of 250 mg/ mL incubated in a thermomixer at 50 °C, 1400 rpm, in order to favor the transgalactosylation reaction instead of substrate hydrolysis. Samples were taken at 3 and 24 h and analyzed by gas chromatography with a flame ionization detector (GC-FID). The enzyme with the highest capacity to synthesize lactitol-GOS was P. acidipropinici LET 120-β-gal which was able to produce 53% of total GOS at 24 h of reaction, with a high production of DI-GOS (30.5%) and no TETRA-GOS detected. B. cirulans was able to synthesize 43% of total GOS with a major production of TRI-GOS (23%) at 24 h whereas K. lactis and A. oryzae were able to produce 28% and 39% of total GOS, respectively. On the other side, L. bulgaricus CRL 450, only synthesized 10 to 13% GOS and displayed higher tendency to hydrolysis. The results obtained show that the production of lactitol-derived oligosaccharides varies depending on the species and could be a strain dependent property. Recently, we reported, for the first time, the production of GOS from lactose by propionibacteria. Although more tests are necessary to determine the structure of lactitol DI-GOS obtained, our results demonstrate the potential of P. acidipropinici LET 120 to synthesize oligosaccharides from lactitol more effectively than recognized commercial enzymes.