Effect of peptide–phenolic interaction on the antioxidant capacity of walnut protein hydrolysates

Abstract

Summary Walnut antioxidant peptides and phenolic compounds (POHs) commonly coexist in walnut protein hydrolysates (WPHs). However, the peptide–phenolic interaction and its effects on antioxidant activities of WPHs remain unknown. Fluorescence and dynamic light scattering were used to study the peptide–phenolic interaction in WPH‐POH mixtures (W‐P) with different POH/WPH ratios; antioxidant abilities of POH only solution, WPH only solution and W‐P were measured with three assays: DPPH radical scavenging, Fe2+ chelation and linoleic acid peroxidation inhibition. Results showed that initially POHs bonded to hydrophobic sites of peptides; subsequently, when POH/WPH ratio exceeded 1:120 (w/w), POHs changed the conformation and average particle size of peptides. Their interaction could at most increase WPHs’ capability in scavenging DPPH radical (44.9%), chelating Fe2+ (36.1%) and inhibiting linoleic acid oxidation (87.5%) at the POH/WPH ratio (w/w) point of 1:12. This research offered a guidance in the production of WPHs with high functionality.

Interaction of Soy Protein Isolate Hydrolysates with Cyanidin-3-O-Glucoside and Its Effect on the In Vitro Antioxidant Capacity of the Complexes under Neutral Condition

“…The λ max of SPI/SPIHs had a slight red shift from 333.5 to 336 nm (SPI), 344.5 to 346.5 nm (SPIH1), 344 to 346 nm (SPIH2), and 345.5 to 347 nm (SPIH3) after interacting with C3G, indicating that tryptophan and tyrosine residues were in a more hydrophilic environment. These results are similar to those obtained in some related studies [ 16 , 24 ]. The K SV , K q values of SPI/SPIHs with C3G are presented in Table 2 to illustrate the fluorescence quenching mechanism.…”

“…In addition, the binding sites between ANS and the hydrophobic groups on the protein surface decreased due to the binding of hydrophobic groups to C3G through hydrophobic interactions [ 5 , 21 ]. Su et al [ 16 ] also observed that as the phenolic compounds/walnut protein hydrolysates ratio ( w / w ) increased from 1:600 to 1:120, the fluorescence intensity of ANS almost decreased linearly, indicating a surface hydrophobicity reduction in their complexes.…”

“…As observed in Figure 5 B–E, the particle size of SPI/SPIHs–C3G complexes became smaller in comparison with SPI/SPIHs alone, and the large particles of the complexes disappeared, mainly due to the strengthened interactions between SPI/SPIHs and C3G [ 5 ]. Related research also found that the addition of a high proportion of walnut phenolic compounds may form compact peptide–phenolic complexes, with a decrease in their average particle size [ 16 ]. The particle size reduction was beneficial to the stability of the beverages [ 3 ].…”

“…However, unlike ABTS, there was no clear correlation between the interaction strength and the antagonistic effect on the DPPH scavenging activity of SPI/SPIHs–C3G complexes, which could be attributed to the fact that the ABTS was more sensitive toward the amino acids and peptides with antioxidant capacities than DPPH. On the other hand, it might be due to the mass ratio of SPI/SPIHs and C3G, and Su et al [ 16 ] observed that when the phenolic compounds/walnut protein hydrolysates ratio ( w / w ) was over 1:12, the DPPH radical scavenging activity of the compounds showed no significant change.…”

“…In one study, Milea et al [ 14 ] improved the functional properties of flavonoids extracted from yellow onion skins through freeze-drying microencapsulation that was obtained with whey protein hydrolysates and different polymer-based coating materials. Moreover, some studies revealed that the number, average peptide length, and amino acid composition of the protein hydrolysate impacted its interaction with polyphenols, thereby changing the antioxidant capacity of the protein–polyphenol complex [ 11 , 15 , 16 ].…”