Fabrication of nanoemulsion-filled alginate hydrogel to control the digestion behavior of hydrophobic nobiletin

Precipitation of hydrophobic bioactive compounds during gastrointestinal (GI) tract usually causes their low absorption and bioaccessibility. In the present work, alginate hydrogel was utilized to encapsulate nobiletin-loaded nanoemulsion droplets, aiming to control the crystallization and release rate of nobiletin. Images by Scanning Electronic Microscopy displayed that nanoemulsion droplets were entrapped in the network of alginate hydrogel matrix. X-ray diffraction results demonstrated that crystallinity of nobiletin in the hydrogel matrix was partially retarded, where nobiletin crystals were softer than those in nanoemulsions. In vitro release rate of nobiletin from hydrogel was much higher at pH 7.4 (>80%) than that at pH 1.2 (<27%). In vitro digestion experimental results revealed that the lipolysis rate of nanoemulsions in the hydrogel was lower than that of bulk nanoemulsions. No nobiletin crystal was formed as hydrogel passed through GI tract. In comparison, many nobiletin crystals were observed in the nanoemulsion systems. The bioaccessibility of nobiletin was determined to be lower in alginate hydrogel (i.e. 44.7± 0.4% at 4.5 mg/mL) than that in nanoemulsions (i.e. 67.2± 0.4% at 4.5 mg/mL). It concluded that nanoemulsion-filled hydrogel could achieve the sustained release and absorption of nobiletin and prevent its precipitation in the GI tract.