Micronized Prinsepia utilis Royle Seed Powder as a Natural, Antioxidant-Enriched Pickering Stabilizer for Green Cosmetic Emulsions

The valorization of agricultural byproducts into functional cosmetic ingredients is a promising strategy for sustainable formulation development. In this work, raw Prinsepia utilis Royle seed residue powder (RPURSRP) which was discarded after oil pressing was upcycled and micronized Prinsepia utilis Royle seed powder (MPURSRP) was obtained by micronization as an eco-friendly Pickering stabilizer. The physicochemical properties of MPURSRP have been studied comprehensively. The results have shown that the MPURSRP (20.28 ± 0.00 μm) exhibited a spherical shape, which is significantly smaller than the RPURSRP (61.49 ± 2.28 μm). The MPURSRP particles tend to reside at the interface between oil and water, allowing them to function as emulsifiers that promote the formation of Pickering emulsions. The emulsifying properties of MPURSRP were investigated systematically. The results revealed that the MPURSRP displayed a better emulsifying performance for non-polar oils. Meanwhile, the existence of polyphenols—an endogenous substance of the Prinsepia utilis Royle seed, endows the prepared Pickering emulsion with good antioxidant activity. As the MPURSRP concentration increased from 0% to 3.0 wt%, more MPURSRP adsorbed at the oil–water interface, and the DPPH radical scavenging rate of the emulsion increased from 9.99 ± 0.63% to 91.71 ± 4.22% (p < 0.001). By upcycling agricultural waste into amphiphilic particles with interfacial properties, we establish a green strategy for stabilizing Pickering emulsions with endogenous antioxidant functionality, offering meaningful guidance toward sustainable colloid systems. This work aligns with the growing demand for natural, bioactive ingredients in green cosmetic formulations.