On-line evaluation of watercore in apples by visible/near infrared spectroscopy

Abstract. Watercore, as an internal physiological disorder affecting apples, can be characterized by water-soaked, glassy regions near the core of apples. It is usually used as the indicator of full ripeness, storage suitability and price setting of apples in many countries. Therefore, fast and non-destructive detection of watercore plays an important role in directly improving apples' commercial value and reducing cost for postharvest industry. In this study, an on-line visible/near infrared spectroscopy (Vis/NIR) system was proposed for real-time detection of watercore in 'Fuji' apples （Malus domestica Borkh.）. Two batch samples (200, 150 samples, respectively) which were harvested from two stages during ripeness in the same orchard were analyzed for both watercore and soluble solids content (SSC). Current results showed that while there was a positive correlation between spectral intensity and watercore severity, no significant correlation was obtained between watercore severity and SSC. The on-line prediction accuracy of SSC subjected to a large interference due to the presence of watercore. Generally, higher than 87.0% of accuracy was obtained for both batches at a detection speed of 3 apples/s for classifying no-watercore from watercore groups using linear discriminant analysis (LDA) coupled with multiplicative signal correction (MSC). In conclusion, the present study verified the feasibility of on-line detecting apples with watercore by Vis/NIR technique, which was useful to design an effective watercore detection instrument for practical application in food industry and storage.