Investigation of the spatial variation of total soluble solids in postharvest mulberry fruit

To better understand the ripening process of mulberry and find a suitable postharvest storage strategy, it is necessary to visualize the quality variation inside mulberry fruit. This study focuses on fast monitoring the Total soluble solids (TSS) variation inside postharvest mulberry fruit using hyperspectral imaging (HSI) technique. Mulberry fruits with different TSS contents were selected at different postharvest periods, and were stored in refrigeration and room temperature as control. During the storage, mulberry fruits were cut at longitudinal sections and hyperspectral images of treated and control fruit were obtained by a visible/near infrared (Vis/NIR) HSI system. When the spectral image acquisition was completed for each fruit, its reference TSS was determined immediately by a handheld refractometer. At last, a robust prediction model between the reflectance spectra of fruits and their TSS references were established using partial least square regression. Results showed that a good correlation was obtained between the reference TSS values and spectral information. The quantitative TSS distribution inside mulberry fruit was visualized. This study presents a rapid method of HSI for visualization of TSS distributions in fresh-cut mulberry fruit. To the best of our knowledge, this is the first study on using hyperspectral imaging to measure TSS distributions inside mulberry fruits. Hyperspectral imaging system supported by multivariate image analysis methods is a powerful tool in evaluating and visualizing the TSS distribution inside mulberry fruit at pixel level.