Bacterial Cellulose Nanocrystal-Stabilized Water-in-Water Pickering Emulsions: Stability, Amylopectin Partitioning, and In Vitro Digestion Behavior

Water-in-water (W/W) Pickering emulsions based on aqueous two-phase systems (ATPS) are promising for food applications, but their stabilization is challenged by the ultra-low interfacial tension inherent to ATPSs. This study developed food-grade W/W Pickering emulsions stabilized by bacterial cellulose nanocrystals (BCNCs) and evaluated their ability to regulate starch digestibility. The effects of dextran (Dex) concentration, maltodextrin (MD) concentration, and BCNC content on the microstructure, rheological properties, and stability of the emulsions were systematically investigated. The partitioning behavior of amylopectin (AMP) between the two phases and the in vitro digestion behavior of AMP-loaded W/W Pickering emulsions in the presence of α-amylase were further examined. Fourier-transform infrared spectroscopy confirmed the successful preparation of BCNCs. The optimal formulation (24 wt% Dex, 14 wt% MD, and 0.24 wt% BCNCs) exhibited a uniform droplet distribution and enhanced storage stability. Contact angle analysis indicated preferential wettability of BCNCs toward the continuous Dex-rich phase, promoting interfacial adsorption and droplet stabilization. The emulsions remained stable at pH 3.0-7.0 but were sensitive to ionic strength above 7 mM sodium chloride. Importantly, in vitro digestion showed that BCNC-stabilized emulsions significantly inhibited α-amylase-mediated hydrolysis of AMP, with the hydrolysis extent reducing from ~54% to 14%. These results indicate that BCNCs act as effective natural stabilizers for W/W Pickering emulsions, forming a physical barrier that retards starch digestion. This work provides a sustainable strategy for designing slow-digestible, low-glycemic-index food systems with potential applications in functional foods and pharmaceuticals.