Nanocelluloses are nanosized materials of crystalline or fibrillar form that exhibit interesting intrinsic properties such as high surface area, crystallinity, wettability, and mechanical strength. Owing to their nanoscale size and good wettability, nanocelluloses can also be applied as solid interface-stabilizing agents known as Pickering particles. Green chemistry-inspired solvents such as deep eutectic solvents (DES) have gained considerable attention compared to organic solvents, as they are inexpensive, have low vapor pressure, are non-flammable, chemically stable, recyclable, biodegradable, and toxicologically well-characterized. Our previous studies have shown that combining DES with ultra-high-pressure homogenization (UHPH) can efficiently transform microcrystalline cellulose (MCC) into cellulose nanofibrils (CNF) with excellent emulsion stabilization capability. The aim of this study was to investigate the Pickering o/w emulsion stabilizing capacity of DES–UHPH-modified CNF at different concentrations and environmental conditions (i.e., temperature, pH, and ionic strength). In addition, the potential of the CNF Pickering emulsions as templates for the delivery of β-carotene was assessed under controlled storage and semi dynamic in vitro digestion conditions.

DES systems composed of choline chloride and urea or malic acid were used for the pretreatment of MCC, following ultra-high-pressure homogenization at 2500 bar. The resulting CNF suspensions were mixed with MCT oil (80/20 w/w) using a sonicator. The obtained emulsions were then stored under different temperature, pH, and salt conditions. The same sonication setup was used for the encapsulation of β-carotene, which was first dissolved in MCT oil. Emulsion storage trials were conducted at 4, 20, 37, 50, and 80 °C, and β-carotene retention was monitored over 30 days. To investigate the in vitro digestion behavior of the β-carotene-encapsulated Pickering emulsion, we applied a novel semi-dynamic digestion system designed to allow gradual gastric/intestinal fluid injection and pH reduction, better simulating human digestion kinetics. Individual pumps with adjustable input rates for different digestive fluids, pH control liquids, and gases were connected to a bioreactor.

Results have shown that the nanocellulose exhibited excellent emulsion-stabilizing capacity across 25–50 °C, pH 4.5–10, and ionic strengths up to 200 mM, demonstrating the effectiveness of DES–UHPH treatments for tuning stabilization mechanisms in Pickering emulsions. Furthermore, the Pickering stabilization effectiveness of nanocellulose particles strongly depends on their morphology, structure, and surface charge density. β-Carotene storage trials showed significantly lower degradation rates in the encapsulated samples compared to β-carotene in bulk oil, especially at high temperatures. In addition, CNF-based Pickering particles efficiently protected β-carotene under UV light. Finally, the implementation of semi-dynamic gastrointestinal digestion, which remains rarely explored due to experimental limitations, offers a more physiologically relevant model than traditional static approaches. The development of nanocellulose-based Pickering systems for encapsulation and delivery of bioactive compounds under such realistic digestion conditions presents substantial potential for advancing understanding and innovation in this field.