The functional behavior at the O/W interface of WPI, ex- pressed as the particle-surface coverage (mg/m2), was studied to elucidate its possible impact on system stability and B-carotene protection. As shown in Figure 2, the surface coverage increased with increasing protein concentration. This inplied that WPI are progressively adsorbed at the O/W interface forming a sort of multilayer structure. WPI were partially denatured at the O/W in- terface (molten-globule state) (Dickinson 1998) allowing protein molecules in the water phase (partially denatured during produc- tion at 50 oC) to "stratify" and form multiple layers via nonpolar, thiol, and disulfide groups. These groups are normally buried in the interior of the native structures of WPI, but, when exposed, at the interface, they could increase the hydrophobic interactions and favor intermolecular disulfide bonding of protein molecules through a thiol disulfide exchange reaction or oxidation, lead- ing to protein cross-linking at the interface