Pickering emulsions immobilized within hydrogel matrix with enhanced resistance against harsh processing conditions and sequential digestion

• Pickering emulsions were immobilized in sodium alginate hydrogel matrix.
• USAXS/SAXS analysis revealed the microstructure of emulsion hydrogels (EGs).
• EGs exhibited enhanced resistance towards harsh processing conditions.
• EGs were stable in gastric digestion and released lipid phase in intestinal fluid.
• Bioaccessibility of curcumin in lipid phase was affected by compositions of EGs.

Protein particles stabilized Pickering emulsions are unstable under harsh processing conditions and vulnerable to premature lipid phase release during gastric digestion. The objective of this study is to encapsulate kafirin nanoparticles-stabilized Pickering emulsions (KPE) within hydrogel matrix to develop orally administrated Pickering emulsions with enhanced storage and sequential release properties. By premixing KPE and sodium alginate with different volume ratios, emulsion hydrogels (EGs) with various emulsion fractions were immobilized within the calcium ions crosslinked sodium alginate hydrogel matrix thereafter. Ultra small-angle x-ray scattering (USAXS)/small-angle x-ray scattering (SAXS) analyses suggested that encapsulation of KPE resulted in shrinkage in hydrogel network mesh size, and the emulsion interface evolved from smooth to course one as volume ratio of sodium alginate to KPE increased. When incubated under alkaline (i.e., pH = 8.5) or high-temperature (i.e., 60 °C) conditions which were previously reported to cause severe structural collapse for KPE, the coalescence and lipid phase release in EGs were largely inhibited. EGs were also found to be less subjective to stimulated gastric digestion, while the collapse of EGs and thus the release of lipid phase took place in simulated intestinal fluid. The volume fraction of alginate in EGs did not affect the ultimate free fatty acid (FFA) release extent, but it had a negative correlation with the bioaccessibility of lipophilic nutraceutical. This study highlights the potential of designing hydrogel carrier for the oral administration of Pickering emulsion with ease of preparation, improved processing stability and controlled digestion profile.

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