Structural analysis of the alpha-D-glucan produced by the sourdough isolate Lactobacillus brevis E25

Authors: DERTLI, ENES - Bayburt University; COLQUHOUN, IAN - Institute Of Food Research - United Kingdom; Cote, Gregory; LE GALL, GWENAELLE - Institute Of Food Research - United Kingdom; NARBAD, ARJAN - Institute Of Food Research - United Kingdom

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2017
Publication Date: 9/7/2017
Citation: Dertli, E., Colquhoun, I.J., Cote, G.L., Le Gall, G., Narbad, A. 2018. Structural analysis of the alpha-D-glucan produced by the sourdough isolate Lactobacillus brevis E25. Food Chemistry. 242:45-52. doi: 10.1016/j.foodchem.2017.09.017.
DOI: https://doi.org/10.1016/j.foodchem.2017.09.017

Interpretive Summary: Lactic acid bacteria are commonly found in fermented foods, where they not only produce the acid they are known for, but also produce gums that modify and thicken the texture of the foods. This paper describes work on some bacteria found in sourdough bread, and methods used to characterize the gums. The research provides new methods and new insights useful for the study of fermented food products, and gives food scientists new tools for the study of food components.

Technical Abstract: Cereal associated Lactic Acid Bacteria (LAB) are well known for homopolymeric exopolysaccharide (EPS) production. Herein, the structure of an EPS isolated from sourdough isolate Lactobacillus brevis E25 was determined. A modified BHI medium was used for production of EPS-E25 in order to eliminate potential contaminants. Analysis of sugar monomers in EPS revealed that glucose was the only sugar present. Structural characterisation of EPS by NMR and methylation analysis revealed that E25 produced a highly branched a-glucan with (a1 '3) and (a1 '6) glycosidic linkages, and was similar in structure to a previously reported EPS from Lactobacillus reuteri 180. The 1H and 13C NMR data were contrasted with newly recorded data for known polysaccharides (alternan, commercial dextran) which also contain a-(1,3,6)Glc branch points. It was found in both the E25 EPS and alternan that the NMR parameters could be used to distinguish glucose residues that had the same substitution pattern but occupied different positions in the structure.