The optimal transglutaminase concentrations to improve the delivery efficiency and cholesterol-lowering ability of novel resveratrol-loaded soybean protein- or soybean peptide-based nanogels

This study aimed to determine the optimal transglutaminase (TGase) concentrations of resveratrol (Res)-loaded soy protein isolate nanogels (SPI-NGs) and soy protein peptide nanogels (SPP-NGs). The encapsulation efficiency (EE), intestinal release efficiency (IRE), and release kinetics models of Res were measured. The structural changes of NGs were observed by DLS, AFM, TEM, SEM, CD, and FT-IR, etc. The composition and activity of digestive products of NGs were evaluated by LC-MS/MS. Results showed that the optimal TGase concentrations for SPIand SPP-NGs were 90 and 900 U/g protein, respectively. The optimal NGs exhibited the appropriate particle size (411.62 nm and 258.85 nm), EE (81.37% and 81.62%), IRE (58.55% and 68.36%), and cholesteryl esterase inhibition rate (16.67% and 44.55%). The gastrointestinal digestion of NGs fitted well with the logistic model (R2 = 0.97-0.99). The optimal NGs showed the slowest digestion rates and exhibited a compact network due to stronger isopeptide and hydrogen bonds, which enhanced the encapsulation effect and decreased the digestion rate. Subsequently, the altered secondary and tertiary structure induced by crosslinking exposed more hydrophobic groups, which led the optimal NGs to release more amino acids and peptides that reduce cholesterol following digestion. The optimal TGase amount for SPP was higher than that for SPI due to more exposed TGase crosslinking sites and free lysine and glutamine released via hydrolysis. Overall, the novel resveratrol-loaded SPI/SPP-NGs were successfully fabricated under the optimal TGase concentration, ensuring the efficient delivery of Res and cholesterol-lowering effect.