Chemical interactions and protein conformations changes during the formation of silver carp surimi gel were studied by textural analysis, chemical methods, laser Raman spectroscopy, and circular dichrosim. The optimum setting time at 40 • C was 60 min. During surimi gel formation, ionic bonds and hydrogen bonds decreased significantly (P ≤ 0.05), while hydrophobic interactions, disulfide bonds, and non-disulfide covalent bonds increased significantly (P ≤ 0.05). Hydrophobic interactions, disulfide bonds, and non-disulfide covalent bonds were the main chemical interactions maintaining the stable structure of surimi gel. Secondary structural analysis of surimi protein showed that 94.11% α-helix existed in native myosin and it partly changed into β-turn and random coil during heating. Myosin gel was made up of 33.70% α-helix, 12.40% β-turn and 53.90% random coil. These three kinds of secondary structures were the main protein conformations in surimi gel.

Proanthocyanidins with different polymerisation degrees were extracted from Chinese quince fruits by subcritical ethanol/water into four fractions (F1-F4), which were then analysed using UPLC-MS/MS, GPC and thiolysis combined with RP-HPLC MS and MALDI-TOF MS (matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry). The inhibitory effects of these proanthocyanidins on the formation of heterocyclic aromatic amines (HCAs), such as norharman, harman and PhIP, in chemical model systems were determined. The results reflected that the mean degree of polymerisation (DP) of proanthocyanidins in fractions F1, F2, F3 and F4 were 8.0, 12.7, 27.5 and 64.9, respectively. All four fractions prominently and dose-dependently reduced the formation of HCAs at concentrations of 0.5, 1 and 2 mg mL −1 in chemical models. F1, the fraction richest in oligomers, had the most effective inhibition of harman, norharman and PhIP, with the levels reduced by 65.71%, 37.15% and 72.99%, respectively, when used at a concentration of 2 mg mL −1 . The mean DP of proanthocyanidins showed negative correlation with the inhibition of HCA formation (R 2 = −0.697 for norharman, −0.799 for PhIP and −0.758 for harman). These findings suggest that proanthocyanidins from Chinese quince fruit have the potential to be used as additives to reduce the levels of heterocyclic amines in foods.

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