Encapsulation of protein nanoparticles within alginate microparticles: Impact of pH and ionic strength on functional performance

• Core–shell protein nanoparticles were prepared by antisolvent precipitation.
• Protein nanoparticles were encapsulated within biopolymer microgels.
• The microgels were fabricated by electrostatic complexation of casein and alginate.
• Encapsulated protein nanoparticles had a wider range of pH and salt stability than free ones.

Incorporation of bioactive proteins into functional foods is often challenging due to their instability to aggregation, sedimentation, or hydrolysis. In this study, core–shell protein nanoparticles, consisting of a zein core and a whey protein shell, were fabricated by antisolvent precipitation. The protein nanoparticles were then incorporated into biopolymer microgels fabricated by electrostatic complexation of casein and alginate. Protein nanoparticles were retained in microgels at low pH (3–5.5), but released at higher pH (6–7) due to microgel dissociation promoted by electrostatic repulsion between anionic casein and alginate. These microgels may be useful for retaining and protecting protein nanoparticles within acidic environments (e.g., stomach), but releasing them under neutral environments (e.g., small intestine). Protein nanoparticles were retained within microgels over a wide range of ionic strengths (0–2 M NaCl, pH 5). Protein nanoparticle encapsulation within microgels may improve their pH and salt stability in functional foods.