Dear Vincent, you may consider NMR as described in ''Characterisation and modification of the exopolysaccharide produced by Lactococcus lactis subsp. cremoris B40'' or FT-IR spectroscopy like in ''Antioxidant activity of phosphorylated exopolysaccharide produced by Lactococcus lactis subsp. lactis''. I am afraid that HPLC might be the most reliable method for the quantitative and qualitative determinations of the structure of exopolysaccharides.