Protein-LMWE mixed monolayers

Surface Shear Characteristics of Protein-LMWE Mixed Monolayers.268... 

From a systematic study focused on fhe tt-A isofherm of protein-LMWE mixed monolayers (including fhe application of fhe additivity rule on miscibility and the quantification of inferacfions between monolayer components by excess free energy ( if has been concluded that, at a macroscopic level, these compounds form a pracfically immiscible monolayer at the air-water interface, af tt < Tlf At higher tt the collapsed protein is displaced from the interface by LMWE (monoglycerides, phospholipids, etc.). The existence of low profein interactions in disordered proteins ((3-casein and caseinate) facilitates the protein displacement by LMWE from fhe air-water interface. However, the lower surface acfivify of unsafurafed-LMWE explains the fact that this lipid has a lower capacity than saturated-LMWE for protein displacement. 

Long-Term Relaxation Phenomena in Protein and LMWE Monolayers.. 263 Spreading and Adsorption of Protein and LMWE Mixed Films at... 

The existence of protein-LMWE interactions depends on the interfacial composition and on the protein/LMWE ratio. In general, the surface activity of the mixed films is determined by the LMWE as the surface pressure of the mixed film is the same as the LMWE equilibrium spreading pressure, and the monolayer is not saturated by the protein. However, the protein determines the surface activity of mixed films as the protein saturates the monolayer. In the intermediate region there exists coexistence of protein and LMWE at the interface. 

Using a unique device that incorporates different interfacial techniques, such as surface film balance and Brewsfer angle microscopy (BAM), we have analyzed fhe sfrucfural characferisfics of profein-LMWE mixed films spread on fhe air-water interface (Pafino ef al., 2003 Lucero, in press). At surface pressures lower than that for profein collapse a mixed monolayer of LMWE and protein may exist. At surface pressures higher than that for protein collapse, collapsed protein residues may be displaced from the interface by LMWE molecules fhaf is, fhe mixed film is practically dominated by LMWE molecules the tt-A isotherms of fhe mixed film are parallel to that of the lipid. 

Surface dilatational rheology is a very sensitive technique to analyze the competitive adsorption/displacement of protein and LMWE emulsifier at the air-water interface (Patino et al., 2003). A common trend is that the surface dilatational modulus increases as the monolayer is compressed and is a maximum at the highest surface pressures, at the collapse point of the mixed film, and as the content of LMWE in the mixture increases. At higher TT, the collapsed protein residues displaced from the interface by LMWE molecules have important influence on the dilatational characteristics of the mixed films. The mechanical properties of the mixed films also demonstrate that, even at the highest tt, the LMWE is unable to displace completely protein molecules from the air-water interface. 

---