Pickering emulsions stabilized by aminated gelatin nanoparticles: Are gelatin nanoparticles acting as genuine Pickering stabilizers or structuring agents?

Abstract

Herein, gelatin was modified with ethylenediamine and processed into nanoparticles, named aminated gelatin nanoparticles (AGNPs). They had higher surface charge and were more hydrophobic compared with native gelatin nanoparticles (GNPs). The freely extending outer polymer layer of AGNPs is easy to be protonated or deprotonated at various pH conditions, giving AGNPs a remarkable size change of 63.23 nm and highly deformable property. AGNPs were then used as stabilizers to fabricate stable oil-in-water (O/W) Pickering emulsions using different edible oils (MCT oil and corn oil) as internal phase with volume fraction up to 85%. Most of AGNPs tended to irreversibly adsorb at oil−water interface to form independent droplets, whereas GNPs favored accumulating in aqueous phase, trapping oil droplets to form three-dimensional networks. The droplet size of AGNPs-stabilized emulsions could outstrip 150 μm and the emulsions still exerted stability against 10 months, centrifugation up to 10000 g, and pH changes. Increasing oil fraction led to form compact packing of oil droplets and in turn improve creaming stability, centrifugation stability, rheology, oxidation stability, as well as retention of encapsulated β-carotene of the emulsions. AGNPs-stabilized emulsions were generally more stable than GNPs-stabilized emulsions and could provide stronger protective features for lipid oxidation or entrapped β-carotene, especially for the cases in corn oil emulsions. Owing to the viscoelastic absorbed AGNPs layers, the surface-active long-chain fatty acids in corn oil and the incorporated β-carotene displayed very limited effect on the stability and microstructure of the emulsions. The findings in this work provided a perspective about ultra-stable Pickering emulsions with independent droplets merely stabilized by protein nanoparticle adsorbed layers, which had potential in encapsulating and protecting easily-oxidized functional ingredients in food and pharmaceutical applications.