Characterisation and modification of the exopolysaccharide produced by Lactococcus lactis subsp. cremoris B40

The chemical structure of an exopolysaccharide produced by Lactococcus lactis subsp. cremoris B40 is studied, explaining earlier reported analytical discrepancies. The EPS was found to have a molecular mass of 6.8 x 10(5) g mol(-1) and a molar ratio of rhamnose:galactose: glucose:phosphorus of 1:1.3:2:1.1. P-31 NMR indicated that a single phosphate group is present as a phosphodiester. EPS B40 was chemically modified using 0.6 M H2SO4, 28 M HF or 2 M NaOH. From these modifications it could be concluded that galactose I-phosphate was linked at the 3-position of 1,2,3,4-linked galactose in the backbone of the EPS. Furthermore, it appeared that during the hydrolysis step of the sugar composition analysis the galactose 3-phosphate linkages were only partially split and that, as a result, the amount of galactose was underestimated in presence of phosphate. Finally, it was demonstrated that a crude cellulase preparation was able to degrade dephosphorylated and partially de-rhamnosylated EPS. (C) 1998 Elsevier Science Ltd. All rights reserved.