Design and characterization of whey protein nanocarriers for thyme essential oil encapsulation obtained by freeze-drying.

Innovative coating powders, based on whey protein concentrate (10-15 wt%) as native (WPC) or denatured protein (d-WPC), solely or in combination with alginate (0.75 wt%, AL), containing thyme essential oil, were produced using the freeze-drying technique. The impact of individual components (protein, alginate and oil) as well as the effect of heat-induced protein denaturation, was resolved regarding physicochemical, thermal and morphological properties of powders. High product yield (∼100%), particle size (223-257 nm), low moisture content (0.10-0.13%) and zeta potential (-19 to -25.6 mV) were determined for all samples. Strong antimicrobial activity of thyme oil nanocarriers against foodborne pathogens was demonstrated. Thermogravimetric analysis (TGA) indicated enhanced thermal stability of encapsulated oil. The most specific bands of structural compounds were identified in Raman spectra of the tested formulations, but principal component analysis (PCA) on recorded spectra was necessary to show the differences between carriers of different wall materials.