Fabrication and Characterization of Cellulose Nanocrystals from the Shells of Juglans regia L. and One-Step Emulsification for Pickering Double Emulsions

The shells of Juglans regia L. are agricultural by-products rich in cellulose, yet they are typically discarded as waste. Conventional surfactant-stabilized double emulsions suffer from instability and potential toxicity, which necessitate the use of sustainable food-grade stabilizers. This study prepared cellulose nanocrystals from Juglans regia L. shells, evaluated their potential, and applied them, in combination with sodium caseinate (NaCaS), to stablize water-in-oil-in-water (W/O/W) Pickering double emulsions (PDEs) via a one-step emulsification. JR-CNCs were produced by sulfuric acid hydrolysis and characterized in terms of morphology, crystallinity, and surface properties. The resulting JR-CNCs exhibited a needle-like shape (average length 130.0 nm, diameter 5.3 nm), a high crystallinity index of 88.28%, and good thermal stability. PDEs were prepared using JR-CNCs together with NaCas at different oil-to-water ratios (8:2 to 5:5). Among them, PDEs with an 8:2 ratio showed a typical W/O/W core–shell structure, elastic-dominated rheological behavior (G′ > G″), and the smallest change in droplet size and zeta potential during 28-day storage, as well as superior centrifugal, thermal, and freeze–thaw stability. Additionally, this formulation exhibited lower levels of lipid oxidation products (lipid hydroperoxides: 38.47 μg/mL; TBARS: 4.07 μg/mL) after 14 days, compared with the other ratios. Simulated gastrointestinal digestion revealed structural changes consistent with gradual destabilization, which suggests potential for delayed release. These findings demonstrate that JR-CNCs are promising eco-friendly stabilizers for food-grade Pickering double emulsions. Future work should include quantitative encapsulation efficiency and release studies using a model bioactive compound, as well as comparison with other natural particles to establish relative performance.