Screening of ß-galactosidase activity of Argentinian lactic acid bacteria for synthesis of prebiotic oligosaccharides from lactose (GOS) and lactulose (OsLu)

Resumen del trabajo presentado al V International Symposium on Lactic Acid Bacteria: "Benefitting from Lactic Acid Bacteria. Progress in Health and Food", celebrado en San Miguel de Tucumán (Argentina) del 19 al 21 de octubre de 2016.The development of functional foods has received great attention from industry due to the high demand of healthy foods by consumers around the world. Among functional ingredients probiotic microorganisms and prebiotic compounds have gained increasing interest by researchers. In this respect, ß-D-galactosidase enzyme possesses a relevant technological value allowing hydrolysis of lactase in dairy products for intolerant population. Also, ß-D- galactosidases are used to synthesize prebiotic galactooligosacharides (GOS) by transgalacto reactions. GOS are non-digestible carbohydrates that modulate the colonic micro in a healthy manner and also have application as functional ingredients. However, depending on the origin of the enzyme and reaction conditions different amounts of GOS and between D-galactose units may be formed which in turn could affect their properties prebiotic potential. Then, in the present work we screened the ß-D-galactosidase activity strains of potential probiotic lactic acid bacteria (LAB) isolated from Argentinean foods order to select the most appropriate strains for GOS and oligosaccharides derived from lactulose (Oslu) synthesis. As a first step, strains were grown in media with lactase as sole source in order to determine the presence or inductionn of the enzyme in different microorganisms. Then, suspensions of LAB that showed growth were mechanically disrupted cell free extracts were assayed for specific enzyme activity by a colorimetric method with as substrate. Synthesized GOS and OsLu were determined by GC-FID and HPLC-RID. According to the results obtained, 28 strains (78%) were able to grow on lactase medium were assayed for their ß-D-galactosidase activity which ranged from 0.01 to 2.55 U/mg. Three Lactobacillus strains (L. delbrueckii subsp. bulgaricus CRL 450, L. paracasei CRL and L. plantarum GS30) with the highest activities were selected to assess their ability synthesize the oligosaccharides from 30% (w/v) lactose or lactulose solutions at pH 6.5, for 48 h of incubation. All microorganisms were able to produce GOS and OsLu (di-, and tetrasaccharides) in the range of 23-38% from lactase and 16-24% from lactulose in to the total sugars present in reaction mixtures. L. delbrueckii subsp. bulgaricus CRL and L. paracasei CRL 200 were the most efficient strains praducing 38% of GOS and 24% of OsLu, respectively, showing higher ß-D-galactosidase activity than Lactozym (commercial enzyme of Kluyveromyces lactis) used as control. Our results show by the first time ptoduction of GOS and OsLu by L. delbrueckii subsp. bulgaricus and L paracasei and encourage further studies on the optimization of synthesis and structure characterization of the oligosaccharides obtained.Peer Reviewe