Research On Interaction Between Lactic Acid Bacteria Exopolysaccharides And Milk Proteins

During yogurt fermentation,exopolysaccharides produced influenced the construction of cubic netted structures in yogurt through its electrostatic interaction with proteins and steric hindrance formed by itself.Finally the interaction had remarkable influence on the gelation property,interface characteristics,stability,texture,flavour and quality of yogurt products.This work studied the influence of adding exopolysaccharides and whey protein on the rheology of yogurt,and analysed the interaction between exopolysaccharides and proteins and its influence on quality of yogurt apparently.Adding exopolysaccharides affects the forming and restructuring of steric net-based structure formed by proteins during fermentation,and the exopolysaccharides adding should be kept in 0.3g/L,otherwise it will reduce the viscosity and bring down the quality of yogurt.More exopolysaccharides addition before fermentation,greater change and earlier disassembling of exopolysaccharides.There are two viscosity peak during fermentation,denser and better structure was formed at first,fragile and discontinuous structure afterward.Strains began to grow when adding 4%whey proteins,dense structure of yogurt was formed when adding 8%whey proteins.When 4%whey protein was added,the viscosity was around 0.2 Pa·s,the viscosity of yogurt fermented with 12%skim milk under the same circumstances was around 1.3 Pa·s.It illustrated that casein is the main constituting part of yoghurt viscosity instead of whey protein.More Whey protein addition,higher viscosity of yogurt and more production of exopolysaccharides.The interaction between exopolysaccharides and proteins observing by SEM was that bacteria embedded in protein aggregate,and connected with proteins by exopolysaccharides chains.The preliminary attractive interaction occurs at the molecular scale where multiple proteins are complexed on a single polysaccharide chain.This onset of interaction is independent of the total macromolecular concentration and the protein to polysaccharide ratio.The pH when exopolysaccharides and casein start to interact is about 5.4 ±0.1,the pH when exopolysaccharides and whey protein start to interact is about 6.1 ±0.1,the pH when exopolysaccharides and milk proteins start to interact is about 5.5 ± 0.1.EPS addition limited the aggregation and precipitation of protein molecules and tended to increase the amount of soluble proteins assessed in supernatant.Exopolysaccharides' nature and charge mainly influenced the effect.In binary system,exopolysaccharides interact with casein mainly through iconic interaction.The reducing of temperature had little effect on the interaction.pH,temperature,ionic strength of the binary system had no significant influence on the interaction of whey protein and exopolysaccharides.