CHITIN PICKERING NANOEMULSIONS WITH SPENT HOP EXTRACT: STABILITY AND BIOACTIVE POTENTIAL

The development of Pickering nanoemulsions has attracted significant interest due to their ability to stabilize systems using biodegradable and biocompatible solid particles, eliminating the need for synthetic surfactants. This work aimed to develop and characterize Pickering nanoemulsions stabilized by chitin nanofibers containing a bioactive extract from hop waste to preserve antioxidant activity. Chitin was extracted from shrimp shells (Penaeus brasiliensis), and the hop bioactive compounds were obtained via supercritical fluid extraction using CO₂ and ethanol as a co-solvent under conditions of 40 °C, 25 MPa, a co-solvent-to-matrix mass ratio of 4:1, 15 min of static extraction, and 60 min of dynamic extraction at a solvent flow rate of 5 mL/min. Chitin dispersions (1% and 3% w/v) in 1% (v/v) acetic acid were subjected to sonication (power of 360 W, tip diameter of 5 mm) for 2 h with intermittent cold-water baths to obtain chitin nanofiber suspensions. Subsequently, hop alcoholic extract (0.5% w/v) was added, followed by 5 min of sonication, producing the Pickering nanoemulsions P1% and P3%. Conventional emulsions (C1% and C3%) were prepared by adding Tween 80 surfactant (5% w/w based on chitin mass) along with the hop waste extract to the chitin suspension, applying the same ultrasonic emulsification procedure. The emulsions were characterized for viscosity-average molar mass of chitin, droplet size, polydispersity index (PDI), and zeta potential (ZP) by dynamic light scattering (DLS), antioxidant activity (ABTS), and morphology by transmission electron microscopy (TEM). Chitin exhibited a viscosity-average molar mass of 427.2 ± 4.0 kDa, a value characteristic of this biopolymer, demonstrating that the ultrasonic treatment preserved the integrity of the polymeric chains. Increasing the chitin concentration from 1% to 3% led to a pronounced reduction in mean droplet size, particularly in the P3% system. After 60 days of storage, P1% and P3% emulsions maintained droplet sizes < 500 nm and PDI < 0.5. Zeta potential remained predominantly above +30 mV over the 60-day period, reflecting the protonation of amine groups in acidic media and ensuring strong electrostatic repulsion and long-term colloidal stability. After 60 days of storage, the P1% and P3% emulsions exhibited the highest retention of antioxidant activity from the hop bioactive extract, achieving ABTS radical inhibition values of 47.6 ± 0.1% and 38.1 ± 0.3%, respectively. This work demonstrates the potential of developing these antioxidant biomaterials for food and pharmaceutical applications, highlighting that integrating green processes (supercritical extraction and ultrasound) actively contributes to sustainable practices.