Structure characterization of a pyruvated exopolysaccharide from Lactobacillus plantarum AR307

A pyruvated exopolysaccharide designated as LPE-1 was isolated and purified from the fermentation broth of Lactobacillus plantarum AR307 and characterized for its chemical structure. The results indicated that LPE-1 contained galactopyranose (Galp) and glucopyranose (Glcp) at a molar ratio of 2: 1. The weight-averaged molecular weight (M-w) of LPE-1 was 605 kDa, with a polydispersity index (PDI) of 1.57, intrinsic viscosity ([eta]) of 3.28 dL/g, Mark-Houwink-Sakurada exponent alpha of 0.65 and gyration of radius (R-g) of 36.10 nm. The results of GC-MS and NMR revealed that pyruvate (Pyr) was found to form cyclic ketals at O-4 and O-6 position of terminal galactopyranose (T-Galp). The backbone of LPE-1 was identified to be consisted of 1,4-beta-D-Glcp (23.19%), 1,4-alpha-D-Glcp (11.38%) and 1,4,6-beta-D-Galp (12.05%), branched by 1,6-beta-D-Galp (38.88%) at O-6 position of 1,4,6-beta-D-Galp residue and terminated by T-beta-D-Galp (5.60%) or T-beta-D-(4,6-Pyr)-Galp (8.90%). A possible structural unit was proposed for LPE-1 as follows: GalP*-(1 -> 6)-beta-D-GalP-(1 -> 6)-beta-D-GalP 3-(->)-6 1 1 6 -> 4)-alpha-D-GlcP-(1 -> 4)-beta-D-GlcP-(1 -> 4)-beta-D-GalP-(-> 4)-beta-D-GlcP-(1 -> where Galp* is either T-S-D-(4,6-Pyr)-Galp or T-S-D-Galp. The presence of pyruvate group in LPE-1 would play an important role in improving the viscosity and plasticity of dairy products. (c) 2021 Elsevier B.V. All rights reserved.