Effects of emulsifier charge and concentration on pancreatic lipolysis: 2. Interplay of emulsifiers and biles

As a direct continuation of the first part of our in vitro study (Vinarov et al., Langmuir2012, 28, 8127), here we investigate the effects of emulsifier type and concentration on the degree of triglyceride lipolysis, in the presence of bile salts. Three types of surfactants are tested as emulsifiers: anionic, nonionic, and cationic. For all systems, we observe three regions in the dependence degree of fat lipolysis, α, versus emulsifier-to-bile ratio, f(s): α is around 0.5 in Region 1 (f(s) < 0.02); α passes through a maximum close to 1 in Region 2 (0.02 < f(s) < f(TR)); α is around zero in Region 3 (f(s) > f(TR)). The threshold ratio for complete inhibition of lipolysis, f(TR), is around 0.4 for the nonionic, 1.5 for the cationic, and 7.5 for the anionic surfactants. Measurements of interfacial tensions and optical observations revealed the following: In Region 1, the emulsifier molecules are solubilized in the bile micelles, and the adsorption layer is dominated by bile molecules. In Region 2, mixed surfactant-bile micelles are formed, with high solubilization capacity for the products of triglyceride lipolysis; rapid solubilization of these products leads to complete lipolysis. In Region 3, the emulsifier molecules prevail in the adsorption layer and completely block the lipolysis.     

Conversion of bile salts from inferior emulsifier to efficient smart emulsifier assisted by negatively charged nanoparticles at low concentrations

Bile salts (BS), one of the biological amphiphiles, are usually used as solubilizing/emulsifying agents of lipids or drugs. However, BS such as sodium deoxycholate (NaDC) can''t stabilize an oil-in-water (O/W) emulsion alone due to its unusual molecular structure. In this paper we report that these emulsifiers with poor emulsifying ability can be transformed to highly efficient emulsifiers by combining with negatively charged particles (silica or montmorillonite). Both together can synergistically co-stabilize oil-in-water emulsions at extremely low concentrations (minimum 0.01 mM NaDC plus 0.003 wt% particles). Moreover, the emulsions can be reversibly switched between stable and unstable triggered by CO₂/N₂ at room temperature. This strategy is universal for emulsions containing different oils (alkanes, aromatic hydrocarbons and triglycerides) and for different BS and offers a generic model for a variety of BS of different molecular structure, which will extend their applications in more technical fields such as emulsion polymerization, biphasic catalysis and emulsion extraction.

Bile salts can be converted to efficient emulsifiers assisted by a trace amount of similarly charged nanoparticles and the emulsions formed are CO₂/N₂ switchable at room temperature.     

A theoretical model for the critical micelle concentration of bile salts

Critical micelle concentration (CMC) is a fundamental parameter in the evaluation of the biological activity of natural and synthetic bile salts. The CMC is logarithmically related to the free energy of solute micellization in aqueous solution. Hydrophobic and hydrogen bonding interaction energies were identified as the primary contributors to this free energy and the logarithm of the CMC was modeled as a linear function of relevant chemical group contributions to the solvent accessible molecular surface area of the solute. The structures (three-dimensional atomic coordinates) of 23 mono-, di-, and tri-hydroxyl bile acids were generated and optimized by energy minimization. The accessible surface area for each structure was computed and partitioned according to calculated charge distribution and polar group orientation. Experimental CMC values were fitted to these computed quantities by least squares multiple linear regression. Two regression equations, based on slightly different surface area partition schemes, were derived and compared. Their significance in explaining the aggregation process and in predicting the CMC of new bile salts is discussed.     

Radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene. IV. Effects of emulsifier concentration and dose rate

Radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene was carried out by batch operation with an initial molar ratio of tetrafluoroethylene to propylene of 3.0 in the emulsifier concentration range of 0.1 to 3.0% and in the dose rate range of 2 × 10⁴ to 2 × 10⁵ R/hr. The effects of emulsifier concentration and dose rate on the polymerization rate and the number-average degree of polymerization are discussed in comparison with the Smith-Ewart theory. The polymerization rate is proportional to the 0.26 power of emulsifier concentration and to the 0.7 power of dose rate. The degree of polymerization is independent of the emulsifier concentration and the dose rate above the critical micelle concentration (CMC) of the emulsifier. These results are not in agreement with the Smith-Ewart theory. It is explained that the termination reaction is a degradative chain transfer of propagating radicals to propylene. On the other hand, the copolymerization in emulsion occurs either below the CMC or in the absence of emulsifier. Under these conditions, however, it is impossible to obtain a copolymer of high molecular weight at a high rate of polymerization because of the presence of a small number of polymer particles formed and the short interval of chain growth in the polymer particle.     

Effects of bile salts on percolation and size of AOT reversed micelles

The effects of two trihydroxy bile salts, sodium taurocholate (NaTC) and 3-[(3-cholamidylpropyl)dimethylammonio]-1-propane sulfonate (CHAPS), on the size, shape and percolation temperature of reversed micelles formed by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in isooctane were studied. The percolation temperature of the reversed micelles decreased upon inclusion of bile salts, indicating increased water uptake. Dynamic light scattering (DLS) measurements showed consistent enlargement of reversed micelles upon addition of the bile salts; the hydrodynamic radius increased sixfold in the presence of 10 mM CHAPS and doubled in the presence of 5 mM NaTC. Inclusion of the enzyme yeast alcohol dehydrogenase (YADH) increased the percolation temperature and distorted the spherical structure of the AOT reversed micelles. The spherical structure was restored upon addition of bile salt. These results may help to explain the increase in activity of YADH in AOT reversed micelles upon addition of bile salts.     

Determination of critical micelle concentration of bile acid salts by micro-calorimetric titration

Critical micelle concentrations (CMC) of sodium salts of cholic, deoxycholic and chenodeoxycholic acids in phosphate buffer (pH 7.92) have been determined from microcalorimetric titration curves. The obtained values of 18.4±0.6, 5.3±0.2 and 7.0±0.2 mM, respectively, for Na cholate, Na deoxycholate and Na chenodeoxycholate are close to literature values obtained by other methods. CMC values for secondary micelles were also obtained. This microcalorimetric titration method gives highly reproducible results and rapid determination of CMC values of bile acid salts.     

Microemulsion polymerization of butyl acrylate. IV. Effect of emulsifier concentration

The oil/water microemulsion polymerizations of butyl acrylate initiated by a water (ammonium peroxodisulfate, APS) or oil (dibenzoyl peroxide, DBP) soluble radical initiator at different emulsifier concentrations were investigated. The rate of polymerization vs. conversion curve shows two intervals. The rate of polymerization is found to decrease with the emulsifier concentration. This finding was discussed in terms of the decrease of both radical and monomer concentration, the chain transfer to emulsifier, desorption of chaintransferred radicals, and the contribution of solution polymerization. The polymerization is faster with APS. In the APS system the rate per particle or the number of radicals per particle increases exponentially with increasing particle size. The particle size and number increase during the whole polymerization. This behavior was discussed in terms of the nucleation of monomer-containing micelles and agglomeration of primary particles during the whole polymerization. © 1995 John Wiley & Sons, Inc.     

Study of the interaction between oxygen and bile salts

The interaction between molecular oxygen and bile salts, previously observed using chemiluminescence techniques, is studied in this paper by electrochemical techniques to further highlight the nature of the interaction. A shift of half-wave potential of the first polarographic wave for the reduction of molecular oxygen was observed in solutions in the presence of bile salts. The shift could be related to different phenomena, such as adsorption of bile salt molecules on the mercury electrode, irreversibility of the oxygen reduction reaction, pH of the solution. Experimental results suggest the exclusion of the above mentioned processes and outline the occurrence of a direct interaction between oxygen and bile salts, where the hydrophobic face of bile salt monomers and/or small aggregates are involved, enhancing so dismutation of superoxide ion produced at the electrode. The presence of bile salts in solutions containing triphenylphosphine oxide, a hydrophobic surfactant, increases also the wave of reduction of molecular oxygen. As a consequence bile salts, beside the well-assessed physiological roles, can behave as oxygen carrier and as antioxidant, preventing the oxidation of biological compounds by superoxide ion.     

Spectroscopic studies on the interaction between acridine orange and bile salts

The structure of sodium deoxycholate (NaDC) micellar aggregates has been previously reported to be helical, and two helical models have been proposed for the micellar aggregates of sodium taurodeoxycholate (NaTDC). Here we report NMR and UV-VIS studies on the interaction between acridine orange (AO) and NaDC or NaTDC aqueous micellar solutions. AO is known to aggregate in aqueous solutions. The addition of NaDC or NaTDC causes the breaking of the AO aggregates, although the binding geometry of the two bile salts with AO seems to be slightly different. The cationic dye interacts mainly with the C₁₈ and C,9 methyl groups of the bile salt molecules. This result agrees with one of the two NaTDC helical models and with some of its possible aggregates, and confirms again the helical structure attributed to the NaDC micellar aggregates within the limits of the experimental conditions tested by us.Devoted to Professor Giovannai Battista Marini Bettolo Marconi on the occasion of his 75th birthday.     

Effects of bile salt exposure on pancreatic duct barrier function and protein release determined by two-dimensional electrophoresis and lectin-affinoblotting.

We analyzed effects of a bile salt on pancreatic duct barrier function and protein release into pancreatic juice in cats, using two-dimensional-electrophoresis and lectin-affinoblotting. Preanalyzed pancreatic juice was perfused along the pancreatic duct following duct exposure to a bile salt. In this case, pancreatic duct mucosa showed a partial loss of barrier function to the leakage of exocrine pancreatic proteins dependent upon molecular weight and charge. The release of a sialic acid possessing protein into pancreatic juice was observed.     

Effect of bile salts on adsorption of cholesterol on silica adsorbent

The adsorption of cholesterol and several bile salts on the surface of modified hydrophobic silica adsorbent from individual and mixed solutions is studied at constant solution pH as a function of the concentration of bile salts. It is shown that, despite the solubilization of cholesterol by bile salts, cholesterol is adsorbed on the adsorbent as an individual compound, i.e. not as a complex with bile salts. The stronger the cholesterol is bound with bile salts, the smaller the value of adsorption. For the quantitative interpretation of adsorption data, a nonelectrostatic model of complexation on the surface is used.     

Effects of emulsifier type and environmental stress on the stability of curcumin emulsion

The objective of this study was to investigate the effects of environmental stress and emulsifier types on the stability of curcumin emulsions. Results showed that Lecithin and Tween 80 presented good emulsifying capacity. The Tween 80 emulsion was the most stable among the four emulsions.

The particle sizes of Tween 80 and whey protein emulsion were relatively smaller than gum arabic and lecithin. Extensive droplet aggregation appeared in whey protein-stabilized emulsions when the pH was approximately isoelectric point (pI) with salt concentration >200?mM. Lecithin emulsion was unstable when pH?≤?6 with salt concentration >100?mM. There was little impact of pH and ionic strength on gum arabic and Tween 80 emulsions. All of the emulsions were stable at temperatures from 30 to 90°C in the absence of salt. These results help characterize the emulsifying and stabilizing abilities of emulsifier types intended for applications in the food industry.