Abstract
Some lactic acid bacteria are able to produce exopolysaccharides that, based on localization, can be distinguished in free and capsular or cell-bound exopolysaccharides (CPS). Up to now, the former were the focus of current research, mainly because of the technofunctional benefits they exhibit on fermented dairy products. On the other hand, CPS affect the surface properties of bacteria cells and thus also the textural properties of fermented foods, but data are very scarce. As the cell surface properties are strongly strain dependent, we present a new approach to investigate the impact of CPS on cell surface hydrophobicity and moisture load. CPS positive and negative Streptococcus thermophilus and Weissella cibaria were subjected to ultrasonication suitable to detach CPS without cell damage. The success of the method was verified by scanning electron and light microscopy as well as by cultivation experiments. Before applying ultrasonication cells with CPS exhibiting an increased hydrophilic character, enhanced moisture load, and faster water adsorption compared to the cells after CPS removal, emphasizing the importance of CPS on the textural properties of fermented products. The ultrasonic treatment did not alter the cell surface properties of the CPS negative strains.
Highlights
The formation of exopolysaccharides is a widespread ability amongst lactic acid bacteria and is closely associated with texture-enhancing effects in fermented dairy products [1,2]
The aim of this study was to evaluate the influence of cell-bound exopolysaccharides (CPS) on the surface properties of lactic acid bacteria cells
With CPS negative strains, we confirmed that the applied ultrasonication treatment did not affect growth kinetics, cell surface properties, and morphology of the ultrasonicated cells
Summary
The formation of exopolysaccharides is a widespread ability amongst lactic acid bacteria and is closely associated with texture-enhancing effects in fermented dairy products [1,2]. Gram-positive bacteria such as Streptococcus (hetero-fermentative) or Weissella (homo-fermentative) are able to produce exopolysaccharides that are freely present in the fermentation medium. Hetero-polysaccharides exhibit a large variety in structure due to differences in monosaccharide composition (mainly glucose, galactose, rhamnose) and in their anomeric configuration, and in regard to functional groups, linkage type, branching, and side chain length [6]. Homo-polysaccharides mainly differ in their glycosidic linkages and degree of branching [7]. Viscosity enhancement, and reduced syneresis of fermented products are only a few factors that have raised interest in microbial, in situ produced free exopolysaccharides and their possible ex situ application such as thickening agents or stabilizers in non-fermented foods [8,9,10,11]
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