Microemulsions (ME) are stable nano-sized emulsions that constitute one of the most effective ways to incorporate lipophilic active compounds into water-based food matrices. Great stability, ...colloidal domain droplets, and optical isotropy are some of the advantages of ME. The present work analyzed the influence of rheological behavior and microstructural characteristics of food microemulsions on the release rate of lipophilic vitamins E and D. A fluid ME was compared to a ME with a higher dispersed phase content and a bicontinuous structure (gel-ME). Additionally, carboxymethyl cellulose (CMC) was added to fluid ME (3.5 and 10 g/100 g), obtaining systems with different apparent viscosities and microstructure. The percentage of released vitamins was determined by HPLC, and mathematically modeled. All ME were characterized using TEM microscopy FTIR, rheological and viscoelastic analysis. Fluid and gel-ME reached higher percentages of vitamin release in a very fast manner, while systems containing CMC showed a matrix-driven nature of the release. Those systems with similar zero-shear viscosity and different microstructure exhibited significantly different viscoelastic behavior. Microemulsions with CMC exhibited a viscoelastic solid type behavior with G’ > G’’. Mechanical spectra were satisfactorily fitted with the Generalized Maxwell model and relaxation time spectra were determined. In the quiescent state, gel-ME exhibited a higher plateau modulus than those containing large amount of thickener in the continuous phase. The relaxation time behavior of the structure could explain the kinetic release of liposoluble vitamins from the inner lipid phase of the microemulsions.
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•Fluid and gel microemulsions (ME) were compared with ME including a thickener.•Rheology, TEM microscopy, and FTIR were used to fully describe the analyzed systems.•Mathematical modeling of vitamins E and D release kinetics, determined by HPLC.•Vitamins release rate depends not only on ME rheology but mainly on microstructure.•Viscoelastic relaxation time spectra modeling explains differences in release rate.
Microemulsions are thermodynamically stable systems that have attracted considerable attention in the food industry as delivery systems for many hydrophobic nutrients. These spontaneous systems are ...highly dependent on ingredients and composition. In this work phase diagrams were constructed using two surfactants (Kolliphor RH40 and ELP), water, sunflower oil, and ethanol as cosurfactant, evaluating their physicochemical properties. Stability of the systems was studied at 25 and 60 °C, monitoring turbidity at 550 nm for over a month to identify the microemulsion region. Conductivity was measured to classify between water-in-oil and oil-in-water microemulsions. The phase diagram constructed with Kolliphor RH40 exhibited a larger microemulsion area than that formulated with Kolliphor ELP.
All formulations showed a monomodal droplet size distribution with low polydispersity index (<0.30) and a mean droplet size below 20 nm. Systems with higher water content presented a Newtonian behavior; increasing the dispersed phase content produced a weak gel-like structure with pseudoplastic behavior under flow conditions that was satisfactorily modeled to obtain structural parameters.
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•Food microemulsions (ME) were prepared with emulsifiers derived from castor oil.•Storage and thermal stability was studied and no changes were detected in a month.•Type and content of emulsifier affected droplet size, but all were below 20 nm.•Viscoelastic behavior and flow behavior were modeled finding structural parameters.•Rheology and conductivity detected transition between ME/bicontinuous structure.
Enrichment of food and beverages with bioactive lipids is an important initiative to improve consumer's health. Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids present in fish oil have been ...reported as those with the greatest bioactivity. Emulsions are an interesting alternative to incorporate functional oil; however, there are few studies on food microemulsions as a way to include this kind of compounds. The present work is intended to deepen the analysis of the Kolliphor RH40 emulsifier with potential application in food microemulsions, characterizing its micellar size and thermo-rheological properties, as well as analyzing the effect of environmental stress on physical and oxidative stability of a microemulsion containing fish oil. No significant changes in droplets size (<15 nm) or in their distribution was observed in a wide range of pH (3–9), ionic strength (0.1–10% CaCl2), centrifuging and different thermal treatments. During freezing, a slight increase in size (<21 nm) was detected, maintaining its optically transparent appearance. The high surface area of the microemulsion droplets led to the decrease in oxidative stability compared to fish oil in bulk. However, when microemulsions were stored at 4 °C, the EPA and DHA contents did not change during storage for 60 days.
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•Emulsifiers derived from castor oil presented micelles size lower than 14 nm.•Thermo-rheological and flow behavior of emulsifiers was modeled.•Microemulsions were stable in a wide range of pH, ionic strength, and temperature.•Oxidation of microemulsions with fish oil increased with the storage temperature.•Refrigerated storage of microemulsions did not alter the content of EPA and DHA.
