CHARGE-DEPENDENT INSERTION OF BETA-LACTOGLOBULIN INTO MONOGLYCERIDE MONOLAYERS

The interactions between beta-lactoglobulin and 1-monostearoyl-glycero l were studied in order to gain insight into protein-gel-phase monogly ceride interactions. Using a monomolecular layer at the air-water inte rface, we determined the insertion of beta-lactoglobulin into the mono glycerides under different conditions of protein and surface charge by varying the pH and/or incorporating charged amphiphiles into the mono layer, respectively, and using subphases with either a low or high ion ic strength. The interactions were quantified by determining the bindi ng of C-14-labeled beta-lactoglobulin to the monolayer. Our results sh ow the importance of electrostatics for binding of beta-lactoglobulin to condensed monoglycerides. Moreover, electrostatic interactions were found to be important for specific insertion of beta-lactoglobulin in to the monolayer. A negatively charged surface in particular allowed p ositively charged beta-lactoglobulin to insert in a surface charge den sity-dependent manner, even at surface pressures as high as 36 mN/m, w hereas under other conditions, the limiting insertion pressure was 32 mN/m. The rheological properties of the monolayer were not affected by the interactions with beta-lactoglobulin. (C) 1997 Elsevier Science B .V.