In this study, we used cherry valley duck carcasses to simulate the production process of braised duck. Freshly prepared marinade was added with different levels (0.01%, 0.02% and 0.03%) of grape seed extract (GSE) and reused for up to 21 times. Samples were collected at different cycles to determine the contents of biogenic amines and nitrite in order to evaluate the inhibitory effect of GSE on the formation of nitrite and biogenic amines during the reboiling process. The results showed that the contents of nitrite, biogenic amines and free amino acids in the stewed soup changed significantly with increasing number of reboiling cycles. Addition of 0.02% and 0.03% GSE had a better inhibitory effect on nitrite in the brine. In addition, GSE also significantly inhibited the formation of putrescine (Put) and tyramine (Tyr), as well as the formation of phenethylamine (Phe) despite its great fluctuations. The content of total free amino acids increased first and then decreased, and the contents of phenethylamine, putrescine, and tyramine were significantly correlated with the contents of various free amino acids in the brine (P < 0.05, P < 0.01). In summary, GSE can effectively reduce the nitrite content and inhibit the accumulation of multiple biological amines (phenethylamine, putrescine and tyramine) during the reboiling of the brine soup.

In order to obtain peptide fractions, duck liver proteins were recovered by isoelectric precipitation, and then hydrolyzed simultaneously by alcalase and flavorzyme. The molecular mass distribution of the hydrolysate was determined by using a gel permeation chromatography (GPC) system followed by fractionation using a combination of gel filtration chromatography (GFC) and reversed phase-high performance liquid chromatography (RP-HPLC). Ten novel peptides with molecular mass less than 1300 Da were identified from the subfraction with high inhibitory effect on cytokine release from macrophages using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The anti-inflammatory activity of the synthetic peptides was tested in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophage cells. Peptides LVYPFPGPI and VIESPPEI inhibited the release of NO from inflammatory cells in a dose-dependent manner, with inhibition percentages of 48.24% and 56.32% at the concentration of 100 μg/mL, respectively. VIESPPEI at the concentration of 100 μg/mL inhibited TNF-α release by 42.48%. Notably, IDVSPDSPDHY showed the strongest ability to inhibit the release of IL-6, with an inhibition percentage of 27.04% at the concentration of 25 μg/mL. This study may provide new ideas for the high-valued comprehensive utilization of duck by-products and their application in safe treatment of inflammation.