Nano-sized self-assemblies of nonionic surfactants as solubilization reservoirs and microreactors for food systems

Abstract

In recent studies we have found unique mixtures of food-grade oils, two or more food-grade nonionic hydrophilic emulsifiers, cosolvent (polyol), and coemulsifiers that self-assemble to form mixed reverse micelles (“the concentrate”) and can be diluted with an aqueous phase, progressively and continuously, without phase separation, and are transformed into bicontinuous structures and finally, upon further dilution, can be inverted into oil-in-water nanodroplets. The “concentrate” is capable of solubilizing nutraceuticals, drugs, antioxidants, and other compounds that are poorly soluble in water or in the oil phase, with 10–20 times more solubility capacity than that of any food-grade oils or water phase. For example, phytosterols were solubilized up to 12 times more than the dissolution capacity of the oil (R-(+)-limonene) for the same compounds. Similarly, the solubilization of lycopene in the concentrate was found to be ca. ten times more than in the corresponding oil. The effects of the guest molecule and microemulsions ingredients on the microstructure transitions and their interfacial reactivity were studied, and the correlation between the surface activity of the guest molecule and its effect on the phase transitions was determined. The advantages of these systems in protecting the solubilizates from environmental reactivity (oxidation), was demonstrated. Lycopene did not oxidize—even after 75 days in an open vessel—if solubilized in the microemulsion medium, while if left unformulated, it was totally oxidized. The systems are unique since they demonstrate significant interfacial reactivity. Maillard reactions between sugars and amino acids, carried out at the O/W interface, can be kinetically controlled better than reactions carried out in the aqueous phase; the products are more regioselective and can form Maillard compounds that are not found in aqueous phase processes. Advanced analytical techniques such as SAXS, PGSE-NMR, and viscosity measurements have been used to evaluate the microstructures of the reverse and direct swollen micelles in both the absence and presence of the guest molecules.