The structure of the extracellular polysaccharide (EPS) from Lactobacillus rhamnosus strain GG has been investigated. In combination with component analysis, NMR spectroscopy shows that the polysaccharide is composed of hexasaccharide repeating units. Sequential information was obtained by two-dimensional (1)H,(1)H-NOESY, and (1)H,(13)C-HMBC NMR techniques. The structure of the repeating unit of the EPS from Lactobacillus rhamnosus strain GG was determined as: [carbohydrate structure: see text]

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Thirteen Lactobacillus and five Pediococcus strains were shown to produce an antimicrobial agent, 2-pyrrolidone-5-carboxylic acid (PCA). PCA inhibited many spoilage bacteria, particularly Enterobacter cloacae 1575, Pseudomonas fluorescens KJLG, and P. putida 1560-2. The antimicrobial activity of PCA did not change at higher temperatures. However, the activity was destroyed rapidly by neutralization with ammonium hydroxide. PCA showed slightly lower antimicrobial activity than lactic acid.