Study on a two‐dimensional correlation visible–near infrared spectroscopy kinetic model for the moisture content of fresh walnuts stored at room temperature

In order to implement the real‐time detection of moisture content in fresh walnuts during storage, a visible–near infrared spectroscopy (NIR) kinetic model of fresh walnuts at room temperature was established. Eight characteristic wavelengths were optimized by the two‐dimensional correlation spectroscopy technology, using the moisture content as the external perturbation. The average moisture content of fresh walnuts at different storage times was analyzed, and a first‐order reaction kinetic model was established (Rp2=.848,RMSEP = 0.119). The spectroscopy information and the moisture content index at the characteristic bands were coupled to establish a partial least square prediction model for the moisture content of fresh walnuts (Rp2=.825,RMSEP = 1.827).The multivariate linear regression analysis was performed with the reflectance at the characteristic band as the independent variable and the moisture content as the dependent variable (p < .0001,R² = 0.873), and the NIR kinetic model for moisture content was established. On this basis, the linear relationship between the storage time of fresh walnuts and the NIR reflectance could be obtained. Results revealed that a two‐dimensional correlation NIR kinetic model for moisture content could quickly detect the moisture content of fresh walnuts. PRACTICAL APPLICATIONS: Fresh walnut is very nutritious and has better taste and flavor than dried ones. In order to remove the bitter taste, the seed coat of fresh walnut needs to be peeled before consumption and processing. With the increase of storage time, the fruit will lose most of its moisture content, making it difficult to peel the seed coat and lose the meaning of fresh food. Therefore, it will be harder to peel the seed coat and process the walnut kernel if the storage time is unknown. This study established a kinetic model for moisture content of fresh walnut during storage based on the visible–near infrared spectroscopy, which may help to further research the storage and processing method of fresh walnut.