Storage properties and time prediction of watercore apples based on L and S bands microwave data

Monitoring the storage properties and time of watercore apples is significant in informing sales and storage. In this study, the microwave dielectric spectra of apples at three different angles in the L and S bands were first measured to evaluate the repeatability. Then, the commonly used one-layer and two-layer expandable polyethylene (EPE) packaging on apple dielectric spectra were analyzed to determine the suitable packaging methods for measuring dielectric spectra. Subsequently, the transmission coefficient ( S 12 , S 21 ), soluble solids content (SSC), firmness, watercore index, weight loss, and color value of watercore apples during storage were analyzed. Finally, the accuracy of several prediction models for watercore index, SSC, firmness, and storage time were compared. Results showed that the S 12 and S 21 spectra of apples at three different angles in the L and S bands exhibited good repeatability. At frequencies of 1750 MHz and 2500–4000 MHz, the EPE net significantly affected the S 12 and S 21 spectra. Physico-chemical indices at the sunlit and shaded points showed similar trends with storage time. The correlation coefficients for the optimal model in predicting watercore index, SSC, and firmness were 0.97, 0.97, and 0.82, respectively. The total accuracy of the prediction set of the optimal model for storage time was 98%, and for different storage days, this accuracy exceeded 90%. This study provides valuable information on watercore and quality variations and predictions of apples during storage. • S 12 and S 21 spectra acquired at three rotation angles exhibited good repeatability. • EPE net had a significant influence on the microwave dielectric spectra. • The watercore was represented as the punctate form at the end of storage. • Storage properties and time can be accurately predicted using microwave data.