Ethanol-induced whey protein gels as carriers for lutein droplets

Lutein-in-safflower oil was dispersed in ethanol-water mixtures to form droplets of nano- and micron scale size. Such dispersions were stabilized by stirring them in a whey protein isolate (WPI) solution, which gelled immediately upon coming in contact with ethanol, entrapping the lutein droplets. Gels were dried in a vacuum oven before storage. The mean droplet size of ethanolic emulsions was in the range of 54.1-1300.2 nm in 30-80% (v/v) ethanol as determined by dynamic light scattering (DLS). Transmission electron microscopy (TEM) images of lutein droplets entrapped in protein gels revealed that their initial droplet size was kept through the gelation and drying processes. Raman spectra of dried gels showed the characteristic peaks of lutein (1008, 1160 and 1529 cm^-1) confirming the chemical stability of lutein through the process. X-ray diffraction data showed no evidence of lutein crystallization, suggesting that lutein remained dispersed within the oil droplets. The residual ethanol content of dried gels was found to be lower than the United States Pharmacopeia (USP) limit. The study indicated that lutein-in-safflower oil readily dispersed in ethanol-water mixtures, forming fine emulsions without the aid of surfactants. Whey protein gels intended for the entrapment of lutein-in-safflower oil droplets were formed by ethanol-induced gelation at room temperature. Ethanol-induced protein gelation is a promising technique for the stabilization of nanoscale to micron scale oil droplets containing heat sensitive compounds.