The modern cosmetic industry is driven by a growing demand for natural, bioactive ingredients and sustainable formulation development. However, the extensive use of natural materials often contributes to significant solid waste, with the processing of fruits and vegetables alone accounting for 25–30% of total solid waste. While solid particles (both inorganic and organic) are increasingly used to form stable Pickering emulsions, the complicated synthesis processes of many cosmetic-grade organic particles limit their practical application. Consequently, there is a clear need to develop natural raw materials, particularly those derived from agricultural byproducts, that can stabilize emulsions sustainably.
To address this, the research explored the valorization of discarded agricultural waste—specifically, the raw Prinsepia utilis Royle seed residue powder (RPURSRP) remaining after oil pressing. This plant residue is known to contain valuable bioactive compounds like polyphenols and gamma-hydroxynitrile glucosides. By upcycling this residue and applying micronization technology, the resulting product, micronized Prinsepia utilis Royle seed powder (MPURSRP), offers a promising, eco-friendly solution. This purely mechanical treatment reduces particle size and optimizes interfacial activity while retaining the powder’s inherent natural antioxidant capacity, thus establishing a green strategy for sustainable colloid systems.
Methods
The discarded raw Prinsepia utilis Royle seed residue powder (RPURSRP) was washed, dried, and then subjected to ball milling at 960 rpm and -15 ± 0.5 °C to yield the micronized powder (MPURSRP). Comprehensive characterization of MPURSRP included image analysis-based particle size measurement, scanning electron microscopy (SEM), three-phase contact angle determination to assess wettability, and interfacial tension assessments. Emulsions were prepared using various oils (1:1 oil–water ratio) and different MPURSRP concentrations, and their stability was systematically evaluated via Emulsification Index (EI) and centrifugal testing. Finally, the antioxidant activity of the stabilized emulsions was determined using the DPPH radical scavenging assay.
Key Findings
• Effective Micronization: The micronization process significantly reduced the average particle size (D50) from approximately 61.49 ± 2.28 µm (RPURSRP) to a smaller, spherical size of 20.28 ± 0.00 µm (MPURSRP).
• Emulsifying Capability: MPURSRP, possessing amphiphilic surface properties and an average sphericity of 0.89, demonstrated strong potential as a Pickering emulsifier. It showed a better emulsifying performance for non-polar oils (like Squalane and Mineral Oil), forming oil-in-water (O/W) emulsions.
• Stabilization Mechanism: The stability of the emulsion is achieved through a combination of the mechanical barrier provided by MPURSRP adsorbed at the oil–water interface and the formation of a three-dimensional viscoelastic particle network structure in the continuous phase.
• Dose-Dependent Stability and Antioxidant Activity: Increasing the MPURSRP concentration improved the density of particles at the interface, thereby enhancing emulsion stability. Furthermore, the emulsion exhibited a dose-dependent increase in antioxidant activity, attributed to the inherent polyphenols within the Prinsepia utilis Royle seed.
• High Antioxidant Efficacy: The DPPH radical scavenging rate of the emulsion increased significantly as the MPURSRP concentration rose, reaching up to 91.71 ± 4.22% at 3.0 wt%, compared to 9.99 ± 0.63% at 0% concentration.
Conclusion: Novelty and Future Implication
The novelty of this research lies in the successful upcycling of an agricultural byproduct, post-oil-extraction Prinsepia utilis Royle seed residue, into a micronized, bio-based functional ingredient (MPURSRP) with dual functionality as both a robust Pickering emulsifier and a natural antioxidant. This work establishes a green strategy for stabilizing colloidal systems using amphiphilic particles derived from agricultural waste, which simultaneously imparts endogenous antioxidant functionality to the product.
The future implications of this work are significant, providing meaningful guidance for sustainable colloid systems and meeting the demand for natural, bioactive ingredients in green cosmetic formulations. Researchers plan to continue studying MPURSRP’s impact on formulation stability and efficacy within complete cosmetic products (including various polyols, oils, and preservatives). Crucially, future efforts will explore combining MPURSRP with chemically synthesized emulsifiers to develop sensitive-skin products, aiming to reduce the overall usage of synthetic components. This approach represents a transformative path for converting plant residues into value-added ingredients for bioactive cosmetics.
Link to the study: https://www.mdpi.com/2079-9284/12/6/281
