A DTA technique for identifying the phase inversion temperature of O/W emulsions

Antibacterial action of lipid nanocapsules containing fatty acids or monoglycerides as co-surfactants

Lipid nanocapsules (LNCs) are a new generation of biomimetic nanocarriers obtained via a phase inversion temperature method and have an oily core of medium-chain triglycerides that is surrounded by a shelf containing a lipophilic surfactant (lecithin) and a hydrophilic surfactant macrogol 15-hydroxystearate. The aim of the present study was to produce LNCs with antibacterial activity by replacing lecithin with other lipophilic surface active compounds, namely medium-chain fatty acids and their 1-monoglycerides, which are known to have antimicrobial properties. Fatty acids and monoglycerides were found to affect the properties of LNCs, such as particle size and zeta potential. Incorporation of a co-surfactant decreased significantly particle size (p⩽0.0039). Furthermore, incorporation of either lecithin or fatty acids with at least 10 carbon atoms yielded LNCs with the zeta potential significantly more negative than that of LNCs composed solely of triglycerides and macrogol 15 hydroxystearate (p⩽0.0310). Moreover, they were capable of decreasing the phase inversion temperature. The activity of the LCNs against Gram-positive S. aureus, including a methicillin-resistant strain, increased with increases in the length of the hydrocarbon tail. Monoglyceride-LNCs were found to be more active than the corresponding fatty acids. The opposite behaviour was observed for Gram-negative bacteria, whereby only caproic acid- and caprylic acid-LNCs were found to be active against these organisms. The monoglyceride-LNCs were bactericidal, and they killed in a time-dependent manner. Fatty acid-LNCs killed in a concentration-dependent manner. A haemolysis assay was performed to obtain preliminary information on the safety of the tested LNCs. In the case of fatty acid-LNCs, the concentrations at which bacterial growth was inhibited were similar to the haemolytic concentrations. However, monoglyceride-LNCs showed antibacterial action at concentrations much lower than those at which haemolysis was observed. In conclusion, monoglyceride-LNCs are promising candidates as carriers for the encapsulation of antibacterial agents, particularly against S. aureus.

Properties and functions of stabilizing agents in food emulsions

This review outlines the state of knowledge concerning the basic processes which underlie the behavior of food stabilizers in practical applications. The stability of emulsions is discussed in terms of the forces acting between macroscopic colloidal particles. These forces include the van der Waals force of attraction, which is always present, and the electrostatic, steric, and hydration forces which may stabilize an emulsion since they can be repulsive. The adsorption behavior at the liquid/liquid interface of classes of typical food stabilizers and the influence of the absorbed layer on the droplet-droplet interactions in emulsions are discussed. Finally, the important effects of the surface-active properties of stabilizers on the mechanisms involved in emulsion formation are described.

The influence of formulation variables on phase inversion temperatures of emulsions as determined by a programmed viscometric technique

A programmed temperature rise viscometric technique has been used to examine the influence of formulation variables on the phase inversion temperatures (P.I.T.) of oil-in-water emulsions stabilized with mixed polyoxyethylene alcohol surfactants. Using a heating rate of 0·5° min−1, the P.I.T. was defined either by a sharp change in apparent viscosity when recording shear stress-rate of shear rheograms for successive emulsion samples, or by the change in shear stress with time for a single emulsion sample. With an overall concentration of 6·00% w/w surfactant mixture of Brij 92 and Brij 96, the P.I.T. was found to rise in an approximately linear fashion as the HLB increased towards the optimum value. When the surfactant concentration was related to the aqueous or oil phase and these phase ratios varied, the P.I.T. changed in a complex manner. Water-soluble additives caused marked changes in the P.I.T. For example, 5·0% w/w sodium chloride depressed the P.I.T. by 17° and 5·0% w/w calcium chloride caused an 11° fall, whereas 2·0% w/w propylene glycol produced a 6° rise. These results followed the same trend as the cloud point of 1·0% w/w aqueous solutions of Brij 96 containing these additives. Linear correlations were obtained between the cloud point and P.I.T. data from which the effect of additives upon emulsion stability may be monitored.