Bitterness-masking assessment of luteolin encapsulated in whey protein isolate-coated liposomes

An unacceptable bitter taste limits the application of luteolin in healthier food systems. In this study, a bitterness-masking assessment was performed on whey protein isolate-coated liposomes loaded with luteolin (WPI-coated liposomes) using an electronic tongue and human sensory test. The physical properties of the WPI-coated colloidal nanocarrier were characterized by zeta potential, average diameter, distribution, and morphology analyses. The results indicated that WPI-coated nanocarrier systems exhibited a uniformly dispersed distribution and spherical morphology. After the comparison of the bitterness value, the bitterness-reducing effect of 5% WPI-coated liposomes was the most significant and reduced the bitterness of luteolin by 75%. Raman spectroscopy and X-ray diffraction analysis demonstrated that the decoration of WPI on the liposomes reduced the free motion of lipid molecules. This promoted the ordering at the polar headgroup area and hydrophobic core of the lipid bilayer, which explained why luteolin-loaded liposomes (uncoated liposomes) and WPI-coated liposomes could reduce the bitterness of luteolin from the perspective of bitter molecular groups. Combined with the Raman spectral data, the bilayer rigidity of 5% WPI-coated liposomes was positively responsive to the stabilization of uncoated liposomes against storage and resistance ability against surfactants. It was proven that the emergence of the surface modification of the WPI coating enhanced the stability of uncoated liposomes. These results may contribute to the use of WPI-coated liposomes as prospective candidates for effective delivery of the bioactive bitter substance in nutraceuticals and functional foods.