Microstructure-driven oxidative stability and gut microbiota modulation of flaxseed oil Nano-capsules: A freeze-drying versus vacuum-drying comparative study.

This study compared freeze-drying (FD) and vacuum-drying (VD) for preparing flaxseed oil nano-capsules (FO NC). Structurally, FD formed a porous matrix, while VD caused flattening and aggregation. Although both methods achieved effective encapsulation, FD-FO NC better preserved heat-sensitive components, exhibited lower moisture content (1.39%) and hygroscopicity (1.89%). During 28-day storage, FD-FO NC showed superior stability: controlled reduction in psize (669.03 to 322.28 nm), higher retention of encapsulation efficiency (90.44% to 65.61% in 3 weeks), and lower peroxide values (<0.7 g/100 g). In vitro fermentation indicated FD-FO NC more effectively modulated gut microbiota, enriching beneficial bacteria and increasing SCFAs production (acetate: 20.07 mmol/L; butyrate: 1.90 mmol/L). The novelty of this work lies in its systematic comparative evaluation of FD and VD for nano-capsules, linking their microstructure and oxidative stability to in vitro gut microbiota modulation and SCFAs production, thereby providing new insights for the design of functionally enhanced delivery systems.