| Microemulsions are thermodynamically stable, transparent isotropic solutions with a lot application in pharmaceutics, cosmetics and oil recovery. Due to a number of technical and practical reasons, the widespread application of microemulsions in many food products is currently limited. However, as a potential delivery system for bioactives, microemulsions recently caused great interest of food researchers. A fully-dilutable of food-grade microemulsion systems with glycerol monocaprylate (GMC) as oil had been fabricated and studied in this paper, the main findings are listed as follows:(1) The pseudotenary phase behavior of microemulsion systems were investigated for different surfactants (Tween20,60,80, glyceryl monostearate and ethylparaben), cosurfactants (ethanol, propylene glycol (PG) and butanol) and their mixing ratios at25℃. The microemulsions phase regions was dramatically increased in the presence of short-chain alcohols, while the solubility proprties of the oil and water phase was impaired by adding superfluous alcohols to surfactant phase. The capability of being diluted by water was determined by the mass ratio of oil and surfactant (Wo/Ws). Fully-dilutiable microemulsions would not be formed when Wo/Ws>1, no matter how much ethanol or propylene glycol was added to. The solubilization of microemulsions could only be enhanced by mixing with compatible surfactants. The fully dilutable food-grade microemulsions had been prepared using Tween80/Ethanol (2/1) as surfactant phase and GMC/PG (2/1) as oil phase.(2) The types of microemulsion were identified by conductivity measurement. Along dilution line T73and T82, water in oil microemulsions were formed with water contents below52wt.%and48%, respectively; oil in water microemulsions were formed with water contents above68wt.%and66%; and bio-continuous microemulsions were formed with water contents between52wt.%to68wt.%. and48%to66%, respectively. Bicontinuous phase could be expanded by increasing the proportion of surfactants.(3) The impacts of environmental stresses (ionic strength, pH, temperature) on the stability and properties of the GMC/Tween80/ethanol/PG/water system were examined by Dynamic Light Scattering (DLS), turbidity measuring, centrifuging and storage test. The results showed that partical size of microemulsions along dilution line T73increased during diluting. Environmental stresses had great influence on T73-100(the oil-based concentrate were diluted with100times mass of water phase) microemulsion. T82-100microemulsion was relatively stable at pH3～8, NaCl concentration of0.1～0.6mol/L, and temperature of0～40℃. After a30-day storage, the partical size of T82-100remained less than35nm.(4) The microemulsions prepared in this paper were exhibited shear thinning at low shear rates and found to be Newtonian up to high shear rates. Apparent viscosity varies as function of the water mass fraction. Bicontinuous microemulsion had high viscosity, while viscosity of O/W micro emulsions was low and could be decreased by adding water. The curves of viscosity-temperature showed that bicontinuous microemulsion recoverd fine, while viscosity of both W/O and O/W microemulsion were different during heating and cooling.(5) Concentrated micromulsions were more stable than T82-100microemulsions even storaged under-18℃-60℃. It’s beneficial to dilute concentrated microemulsions to O/W microemulsions after storage and transportation.(6) In this paper, The T82microemulsion had an effective antibacterial activity to the common food-borne bacteria(Staphylococcus aureus and Escherichia coli). And their minimum inhibitory concentration (MIC) were both165mL/L. The bactericidal activity of the microemulsion was due predominantly to the components. Microemulsion may reduce the antibacterial activity of glycerol monocaprylate. |
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