Evaluation of quality changes in big‐eye tuna (Thunnus obesus) based on near‐infrared reflectance spectroscopy (NIRS) and low field nuclear magnetic resonance (LF‐NMR)

Abstract The purpose of this study was to investigate the effect of temperature fluctuations on quality of big‐eye tuna ( Thunnus obesus ). In this work, different logistical processes, including cold chain (CK) and cold chain breaks (L1, L2), were simulated. Near‐infrared spectroscopy (NIRS) and low‐field nuclear magnetic resonance (LF‐NMR) were used for determination the quality changes. Meanwhile, water holding capacity (WHC), water activity ( a w ), sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE), and scanning electron microscope (SEM) were measured. The results indicated that WHC dropped more than 20% in L2 group and the degradation rate of protein was accelerated with the increase of temperature for 216 hr. The curve of NIRS was showed the certain changing trends and its absorbance value showed a downward tendency, which had a decrease from 0.7 at 192 hr to CK > 0.4, L1 ≈ 0.4, L2 < 0.4 at 216 hr. The NIRS further exhibited the changing trend of freshness, which consistent with the results of WHC, SDS‐PAGE and SEM. LF‐NMR showed that immobilized water ( T 22 ) decreased while free water ( T 23 ) increased during processes. The results were coincidence with other indexes. Therefore, NIRS combined with LF‐NMR could effectively reflect the quality changes of big‐eye tuna during circulation. Practical applications Near‐infrared spectroscopy (NIRS) and Low‐field nuclear magnetic resonance (LF‐NMR) can be used to estimate the protein change and water migration of fish. This study indicated that NIRS and LF‐NMR could better characterize the quality change of big‐eye tuna during logistical processes. Moreover, this study provided a theory foundation for the application of NIRS and LF‐NMR on aquatic products.