From molecular interactions to functional enhancement: unraveling the non-covalent binding between Perilla seed protein fibrils and structurally diverse polyphenols.

Plant protein fibrils have gained increasing attention as promising delivery carriers for hydrophobic bioactive compounds. In this study, perilla seed protein fibrils (PSPF) prepared via acid-heat induced self-assembly were used to systematically investigate the non-covalent interactions with four structurally different polyphenols (quercetin, luteolin, naringenin, and curcumin) at pH 3.5. The functional properties and delivery potential of the non-covalent complexes were also evaluated. Thermodynamic analysis and molecular docking demonstrated that hydrogen bonds, van der Waals forces, and hydrophobic interactions dominated the non-covalent binding of PSPF toward polyphenols. Particle size and transmission electron microscopy demonstrated polyphenol complexation mediated PSPF assembly and facilitated the formation of network structures, and the PSPF-quercetin complex (PSPF-Q) possessed the maximum particle size of 690.53 nm. Fourier transform infrared spectroscopy suggested that non-covalent binding of polyphenols strengthened structural ordering of PSPF and promoted the transition from intermolecular (decreased from 72.07% to 54.77%-70.18%) to intramolecular hydrogen bonds (increased from 27.93% to 29.82%-45.23%). Furthermore, quercetin exhibited strong binding affinity toward PSPF (-7.645 kcal/mol) owing to its abundant phenolic hydroxyl groups. For PSPF-Q, the emulsifying activity index and emulsifying stability index increased by 28.91% and 33.60%, respectively; foaming capacity and foaming stability were elevated by 18.23% and 208.68%; and DPPH, ABTS and FRAP antioxidant capacities were enhanced by 296.97%, 267.26% and 170.20%. In vitro digestion results revealed that PSPF effectively achieved sustained intestinal controlled release of encapsulated polyphenols. These findings offer theoretical and experimental support for the design and application of protein fibrils in polyphenol delivery systems.

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