Effect of pre‐frying on distribution of protons and physicochemical qualities of mackerel

Abstract BACKGROUND In this work, low‐field nuclear magnetic resonance (LF‐NMR) and magnetic resonance imaging were used to investigate the changes in protons (from water and oil) distribution of mackerel during the frying process. The relationship between proton migration and some physicochemical indexes was established by partial least squares regression (PLSR). The changing mechanism of the quality characteristics and physicochemical properties of fish meat under different frying conditions was analysed by LF‐NMR combined with PLSR, which provided theoretical support for the development of canned mackerel food. RESULTS LF‐NMR results showed that three kinds of T 2 protons assigned to protein–water interaction ( T 21 ), multilayer bound water ( T 22 ), oil and free water ( T 23 ), respectively. As the frying temperature increased, protons from the T 22 peak significantly decreased, while protons from the T 23 peak remarkably increased. The microstructure of fried mackerel was destroyed; cooking loss, oil content, a * value, b * value, hardness and chewiness increased; and the protein content and L * value decreased. Furthermore, PLSR analysis revealed that significant correlation was observed between the cooking loss, TPA parameter (chewiness), colour parameter ( L *) and LF‐NMR parameters. CONCLUSION Different frying temperatures and times had a strong effect on the physicochemical properties of mackerel. Good prediction models could be established by proton migration using the LF‐NMR technique and PLSR for fried mackerel. Quality control of fried fish could be realized by monitoring the change in LF‐NMR data. © 2021 Society of Chemical Industry