Structure-property relations of \textgreekb-lactoglobulin/\textgreekk-carrageenan mixtures in aqueous foam

There is a great interest in mixed protein/polysaccharide layers at air-water interfaces due to their ability to stabilize aqueous foams. Properties of \textgreekb-lactoglobulin (BLG)/\textgreekk-carrageenan mixtures at different \textgreekk-carrageenan concentrations were studied using foam analysis and molecular-level characterizations at the air-water interface. Because air-water interfaces are a major element in aqueous foams, they were investigated with a combination of interface-sensitive methods such as sum-frequency generation (SFG) as well as surface tensiometry. Using SFG spectroscopy we provide new information on the changes in the interfacial charging state and composition when the BLG/\textgreekk-carrageenan mixing ratio changes. \textgreekk-carrageenan is only weakly surface active as it does not lower the surface tension to a large extend. However, BLG/\textgreekk-carrageenan mixtures showed a synergistic effect because the formation of complexes at the air-water interface and in the bulk solution can favorably influence foam stability. BLG (7.5 µM) was mixed with different \textgreekk-carrageenan concentrations from 0 to 1 mM while the bulk pH was adjusted to pH values which are below (4.5), slightly above (5.6) and well above (7.0) the isoelectric point of BLG. At pH 4.5, the positive \textgreekz-potential of BLG was drastically reduced to negative values and large aggregates in the bulk formed that showed a reduced surface activity and caused also a reduced net charging state at the airwater interface. The interfacial and bulk properties at pH 4.5, resulted in a poor stability of foams that were likely only stabilized by the weak electrostatic disjoining forces in the foam lamella. At pH 5.6 and 7, cooperative     «

There is a great interest in mixed protein/polysaccharide layers at air-water interfaces due to their ability to stabilize aqueous foams. Properties of \textgreekb-lactoglobulin (BLG)/\textgreekk-carrageenan mixtures at different \textgreekk-carrageenan concentrations were studied using foam analysis and molecular-level characterizations at the air-water interface. Because air-water interfaces are a major element in aqueous foams, they were investigated with a combination of interface-sensitive...     »