Helena Ljusberg-Wahren

Aqueous lipid phases of relevance to intestinal fat digestion and absorption.

The phase behavior of monoglyceride/water systems, with oleic and linoleic acid as the dominating fatty acid residues, was investigated. Increased solubilization of triglycerides (oil) or oleic acid in the cubic liquid-crystalline phase formed by monoglyceride and water resulted in the formation of a reversed hexagonal liquid-crystalline phase followed by an L2-phase. The liquid-crystalline phases have different dispersion properties compared to each other in dilute micellar bile salt solutions. The cubic phase is found to be easily dispersed. The relevance of aqueous lipid phases other thah micellar is discussed in relation to intestinal lipid digestion and absorption.

Acyl migration and hydrolysis in monoolein-based systems

The extent of acyl migration and hydrolysis phenomena in glycerol monooleate/water based systems and how they are affected by acetic acid and oleic acid has been examined. To facilitate analysis and interpretation of the data, samples with a low water content, 2–5 wt%, which form a liquid reverse micellar, L2, phase, were chosen. Acyl migration and hydrolysis were monitored versus time by 13C NMR analysis. In addition, the acid value to monitor hydrolysis has been also determined. The formation of small amounts of glycerol-2-monooleate as well as hydrolysis products was observed. These phenomena depend on the water content and storage conditions. The implications of these findings for the observed phase behaviour of the glycerol monooleate/water system are discussed.

A comparison of the phase behaviour of the monoolein isomers in excess water

Abstract Contrary to the 1-isomer, 2-monoolein (2-oleoylglycerol) forms a lamellar liquid crystalline phase with excess water. The difference in phase properties between the two isomers is discussed in relation to differences in the molecular geometry and is related to observations on variations in fat absorption related to positional isomers of triglycerides.

Phase properties and structure of a monoglyceride/sucrose/water system

Abstract The phase behaviour of a sunflower oil, monoglyceride/sucrose/water system was studied at 30°C. The different phases were identified by low-angle X-ray diffraction and polarization microscopy. The main feature of the phase diagram is the transition from a cubic phase to a reversed hexagonal phase (H II ) when sucrose is added to the monoglyceride/water mixture. A similar phase behaviour was also shown to occur for monoolein/sucrose/water, as well as in the corresponding systems when sucrose was replaced by trehalose, fructose and glucose, respectively. The phase transition from a cubic phase to a H II phase, when sugar is introduced to a monoglyceride/water system, corresponds to an increased average wedge shape of the lipid molecule. One explanation for this phenomenon is a structural change of the lipid caused by interaction between the sugar and the hydrated polar head group, thus reducing the interfacial area of the polar region at the contact zone with water.

A Raman spectroscopy study of mixed bile salt-monoglyceride micelles

Abstract A Raman spectroscopy study of sodium cholate/monoglyceride mixed micelles is reported, using perdeuterated 1-monostearin. The C-D stretching vibration region of this micellar solution has been compared with different states of the perdeuterated monostearin with known structures: crystals, an aqueous gel phase, aqueous liquid crystalline phases of lamellar and cubic type, the liquid state and an ethanol solution. Also other spectral regions sensitive for conformation of lipid molecules were examined. The results are consistent with the lamellar type of structure proposed by Mazer, Benedek and Carey for lecithin/bile salt mixed micelles.

Studies on the Interactions Between Mucin and Surfactant Aggregates Containing the Cationic Surfactant Dodecyl Betainate

The interactions of surfactant aggregates containing the cationic, cleavable surfactant dodecyl betainate (DB) with mucin are investigated. The aggregates were either mixed micelles of DB and the nonionic surfactant PS-80 in different ratios or a dispersion of the commercial self-emulsifying drug-delivery formulation Sandimmun Neoral “charged” with DB. It is found that for the surfactant aggregates to show any notable interactions with mucin these must have a high positive charge density. Also presented are results from Ussing chamber experiments, which suggest that DB has a limited impact on the integrity and the barrier function of the intestinal epithelium.

EFFECT OF BILE SALT ON THE THERMAL BEHAVIOR OF A MONOGLYCERIDE-WATER SYSTEM

ABSTRACT The thermal behavior of aqueous mixtures of monoglyceride and cholate has been examined by differential scanning calorimetry. The temperature of the maximum heat capacity for the a-gel to melt transition decreases monotonically with increasing cholate content. The existence of a large liquid region in the ternary phase diagram monoglyceride-cholate-water at 50°C is demonstrated.