Protective, controlled-release and embedding mechanism of porcine plasma protein cold-set gel on quercetin: An effective carrier of hydrophobic compounds

Protection and embedding of hydrophobic bioactive compounds using protein hydrogels are emerging focus during the latest decade. In present study, we fabricated the porcine plasma protein (PPP) cold-set gel by microbial transglutaminase (MTGase) and glucono-δ-lactone (GDL) as coupling precursors. As a result, the embedding, protection and controlled-release effect of the gel on vulnerable hydrophobic bioactive components (quercetin (Que) as representative) with proposed molecular mechanisms were investigated in detail. The results showed that high concentration of Que (5 mmol/L) could be loaded with PPP cold-set gel and embedding efficiency (EE) was over 98%. Compared with free Que, the embedded one exhibited significantly higher thermostability, photochemical stability and storage stability (P < 0.05). In addition, the gel loaded with 5 mmol L−1 of Que had higher swelling potency under gastric (low pH) media and controlled release performance following simulated intestinal digestive pathway. Water holding capacity (WHC) implied that free water molecules played less role in the retention ability of Que in fabricated gel network. Spectral-assisted structural characterization proved that Que was efficiently embedded mainly by generating PPP-Que complex through hydrogen bond and van der Waals force, and the binding site was mainly near Trp residue. This work gave novel insight into the potential use of PPP cold-set gel as an excellent carrier towards protection and selective delivery of vulnerable small hydrophobic nutraceutical compounds.