Fabrication and\nOptimization of Pickering Emulsion\nStabilized by Lignin Nanoparticles for Curcumin Encapsulation

Abstract

To develop reversible pH-responsive emulsifiers of natural\norigin,\nalkali lignin (AL) was used to develop oil-in-water Pickering emulsions.\nAL was first modified to synthesize quaternized alkali lignin (QAL),\nwhich displayed pH-responsive properties and demonstrated solubility\nin both acidic and alkaline solutions. In contrast, QAL exhibited\ninsolubility and formed particles in neutral solutions, thereby making\nit a suitable candidate for utilization as an emulsifier in doubly\npH-responsive Pickering emulsions. At pH 5–9, the emulsions\nwere stable. Above or below this pH range, the system demulsifies,\nresulting in a reversible Pickering emulsifier with two pH-controlled\ntransitions. On the basis of this pH-dependent behavior, lignin-based\nPickering emulsions (LPE) could be subjected to several cycles of\nemulsification–demulsification by alternating the pH of the\naqueous phase between basic and acidic, while the droplet size and\nstorage stability were maintained. Curcumin was used as a drug model\nto study the loading/release behavior of LPE, finding that 50.08%\nof curcumin could be encapsulated in LPE. The <i>in vitro</i> release of curcumin was pH-dependent. In addition, LPE exhibited\nan outstanding protective effect against the ultraviolet-induced degradation\nof curcumin.