The relevance of exopolysaccharides to the rheological properties in milk fermented with ropy strains of lactic acid bacteria

The subunit structures from a number of different species of lactic acid bacteria are now known, with many of the structures being published only in the last five years. The nuclear magnetic resonance spectra to date show around twenty different subunits and molecular mass determinations suggest that these exopolysaccharides occur as very large molecules, frequently greater than 1×106 Da. The physical properties of these molecules will be influenced by their mass and also by the subunit structure. Milk however is a complex medium and studies concerned with effects on rheology of milk as a result of in situ production of exopolysaccharides from these bacteria have to consider many factors. Studies have found that it is not only the nature of the exopolysaccharide, but that the amount produced, the acidity of the milk, the composition of the milk and the length of fermentation, also influence final texture.