Abstract: Objective: To explore the characteristics of the cell structure of walnut kernels and its changes during oxidation for the purpose of obtaining an in-depth understanding of the oxidation mechanism of walnut kernels. Methods: Optical and transmission electron microscopy were used to observe the cell structure of walnut kernels, and its changes during ambient storage and accelerated storage at 60 ℃ were comparatively analyzed as well as changes in peroxide value and the Raman spectral intensity of unsaturated double bonds. Moreover, the correlation of change in the cell structure with peroxide value and the Raman spectral intensity was evaluated. Results: The basic structure of walnut kernels consisted of endotesta, cortical layer and storage cell tissues. The storage cells were filled with protein and oil bodies. As the degree of oxidation increased, the surface of the protein bodies changed from smooth to rough, the oil body membrane gradually shrank until collapse, and the protein bodies became non-uniform in diameter with a tendency of migration and aggregation to one side of the cells. The gap between the cell wall and the oil body membrane increased, the cell wall shrank and became non-uniform in thickness with the mesohyl layer blurring. Conclusion: Changes in protein and oil body membrane structure have a good correlation with the peroxide value and Raman spectral intensity. Raman spectrum analysis can accurately reflect the oxidation characteristics of walnut oil at normal temperature.

Key words: walnut kernel; oxidation; cell structure; Raman spectral intensity; change