Surface behaviour of long-chain lipolytic products (a 1-to-1 mixture of oleic acid and diolein) spread as monomolecular films in the presence of long-chain triglycerides

Abstract

Surface pressure-molecular area curves of pure and mixed monolayers of lipolytic products (a mixture of oleic acid and 1,2-dioleoyl- sn-glycerol (OA-DO) at a 1:1 molar ratio), oleic acid (OA) and purified soybean oil (TG) spread at the argon-water interface were obtained. The results reveal that OA-TG and (OA-DO)-TG mixtures behave ideally when spread over a subphase at pH 8.0. We also determined the surface pressure-molecular area curves of lipolytic products (OA-DO) at the argon-water interface in the absence or presence of an excess of triglycerides. In the presence of an excess of TG, the films of OA-DO can be compressed up to surface pressures identical to the collapse pressure of the OA-DO when present alone. Furthermore, the fact that at the collapse pressure, the area occupied by the OA-DO mixture was the same in both the absence and presence of TG showed that under the experimental conditions used, negligible amounts of lipolytic products were dissolved in the oil and aqueous phases at both pH 5 and pH 8. The fraction of the surface occupied by OA-DO molecules varied from 80 to 100% at surface pressures ranging from 18 to 30 mN m −1.