초록
<P>This work describes an efficient enzymatic synthesis and NMR structural characterization of the trisaccharide β-<SMALL>d</SMALL>-galactopyranosyl-(1→4)-β-<SMALL>d</SMALL>-fructofuranosyl-(2→1)-α-<SMALL>d</SMALL>-glucopyranoside, also termed as lactulosucrose. This oligosaccharide was formed by the <I>Leuconostoc mesenteroides</I> B-512F dextransucrase-catalyzed transfer of the glucosyl residue from sucrose to the 2-hydroxyl group of the reducing unit of lactulose. The enzymatic reaction was carried out under optimal conditions, i.e., at 30 °C in 20 mM sodium acetate buffer with 0.34 mM CaCl<SUB>2</SUB> at pH 5.2, and the effect of factors such as reaction time (0–48 h), enzyme charge (0.8, 1.6, and 2.4 U mL<SUP>–1</SUP>), and sucrose:lactulose concentration ratios (20:40, 30:30, and 40:20, expressed in g/100 mL) on the formation of transfer products were studied. The highest formation in lactulosucrose was attained at 8 and 24–32 h by using 20%:40% and 30%:30% sucrose:lactulose mixtures, respectively, with 1.6 or 2.4 U mL<SUP>–1</SUP> dextransucrase, leading to lactulosucrose yields of 27–35% in weight respect to the initial amount of lactulose. Furthermore, minor tetra- and pentasaccharide, both probably derived from lactulose, were also detected and quantified. Likewise, the capacity of lactulosucrose to act as <SMALL>d</SMALL>-glucosyl donor once the sucrose was consumed, could explain its decrease from 16 to 24 h when the highest charge of dextransucrase was used. Considering the chemical structure of the synthesized oligosaccharides, lactulosucrose and its derivatives could potentially be excellent candidates for an emerging prebiotic ingredient.</P><P><B>Graphic Abstract</B><BR><IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jafcau/2012/jafcau.2012.60.issue-42/jf303335m/production/images/medium/jf-2012-03335m_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jf303335m'>ACS Electronic Supporting Info</A></P>