Liquid foams with a lifetime of several days co-stabilized by monodisperse protein nanoparticles and mechanically stable starch nanocrystals

Abstract

Liquid foams stabilized by protein nanoparticles generally have a lifetime less than several hours because of poor interface and unavoidable coalescence, which strictly limits their applications in, e.g., coffee toppings and milk shakes. In this study, stable foams with a lifetime of several days were prepared by protein nanoparticle-starch nanocrystal (SNC) complexes. The nanoparticles of rice proteins (RPs) or rice bran proteins (RBPs) were prepared by neutralization of their alkaline solutions by cationic exchange resins (CERs) that displace Na+ by releasing H+, leading to the formation of monodisperse, 20-nm nanoparticles facilitating diffusion to the water-air interface. The complexes were assembled by simply mixing proteins with SNCs, affording the formation of quite dispersed network structures (RP@SNCs or RBP@SNCs). During whipping, the protein nanoparticles performed as the diffusion initiators from the continuous phase to the biphasic interface, whereas the SNCs stabilized the interface and functioned as the spacers preventing the approaching of adjacent bubbles in the continuous phase. Moreover, RPs and RBPs had different affinities to SNCs, resulting in foams of varied stabilities. Our study represented a compelling example of structuring stable foams taking joint advantages of diffusion behaviors of protein nanoparticles and biphasic stabilization of SNCs.