Extraction optimization and screening of antioxidant peptides from grass carp meat and synergistic-antagonistic effect.

Grass carp (Ctenopharyngodon idellus) is one of the three most cultivated freshwater fish around the world, but it is mainly consumed afresh, so only a small part of them are processed into salted fish or snack food. This research was performed to prepare and screen antioxidant peptides from grass carp muscle to promote its high-value utilization. The parameters of double-enzyme two-step hydrolysis were optimized, the peptides with the highest ABTS.+ scavenging ability were enriched and identified by Sephadex G-25 and LC-Q-Orbitrap-MS/MS. The synergistic-antagonistic effect among identified peptides was also investigated. The optimized conditions were hydrolyzed with protamex (10,000 U/g) at pH 8.0, 50°C for 3 h, followed by hydrolysis with alcalase (6,000 U/g) at pH 9.0, 50 °C for 2 h, and the protein-liquid ratio was 4%. The hydrolysates were further fractionated to obtain five fractions, in which fraction 3 (F3) exhibited the strongest ABTS.+ and O 2 · - scavenging ability with the IC50 values of 0.11 and 0.47 mg/ml, respectively. Twelve novel antioxidant peptides were identified, in which VAGW possessed the highest activity (139.77 µmol GSH/g). Significantly synergistic effects were observed on the two and three peptides' combination among VAGW, APPAMW, LFGY, FYYGK, and LLLYK, while the C-terminal tryptophan (Trp) played an important role in the synergism. This study found that grass carp muscle hydrolysates can be potential natural antioxidants in functional products. The synergistic effects among peptides may provide a perspective for the combined application of peptides.

Mitigation of isoquercitrin on ß-lactoglobulin glycation: Insight into the mechanisms by mass spectrometry and interaction analysis.

Formation of advanced glycation end products (AGEs) on foods imposes threats to human health after intaking. This research firstly evaluated the inhibition of isoquercitrin on ß-lactoglobulin (ß-Lg) glycation, the mechanisms were elucidated by fluorescence spectroscopy, Orbitrap MSn and molecular docking. Fluorescence spectra indicated that isoquercitrin effectively alleviated the formation of AGEs, it could stabilize the conformation structure of glycated ß-Lg (G-ß-Lg), change the micro-environment in the vicinity of chromophores. SDS-PAGE analysis revealed the suppressed cross-linking of G-ß-Lg induced by isoquercitrin. The number of glycation site detected on G-ß-Lg was reduced from ten to eight after the addition of isoquercitrin, and the relative glycation degree of substitution of per site (RGDSP) of most glycation sites were also greatly decreased. As indicated by intermolecular interaction, isoquercitrin quenched the fluorescence of ß-Lg via a static mechanism, and their combination is an endothermic processing mainly derived by hydrophobic interaction, hydrogen bonds, and van der Waals forces. Isoquercitrin interacted with ß-Lg to form an equimolar complex, and one hydrogen bond was formed between isoquercitrin and Lys69 (4.96 Å). Above results proved that isoquercitrin can be a promising anti-glycation agent used in food system to prevent the formation of harmful glycation products.

Mechanisms of isoquercitrin attenuates ovalbumin glycation: Investigation by spectroscopy, spectrometry and molecular docking.

This research firstly investigated the inhibitory effect of isoquercitrin (ISQ) on Ovalbumin (OVA) glycation. The mechanism was elucidated through the interaction between OVA and ISQ, and changes in glycation sites and degree of each site as deduced by spectroscopy, spectrometry and molecular docking. ISQ significantly inhibited OVA glycation by attenuating the conformational change induced by glycation. It quenched the fluorescence of Trp via static mechanism, and exposed Trp residues to a more hydrophobic surroundings. Formation of OVA-ISQ complex was a endothermic processing driven by hydrophobic interactions, van der Waals forces and hydrogen bonds. LC-Orbitrap-MS/MS revealed that ISQ altered the location of glycation and alleviated the glycation degree of most sites. Molecular docking results indicated that ISQ inserted into the hydrophobic pocket of OVA with six hydrogen bonds and one π-π stacking formed between ISQ and the amino acid residues of OVA, leading to the altered glycation activity of some sites.