Identifying fruit characteristics for non-invasive detection of sunburn in apple

Sunburn of apple fruit is one of the major problems in fruit production areas with high light and temperature environment. Fruit with sunburn are predisposed to develop postharvest disorders and need to be separated from the fruit considered for mid to long-term storage. In order to identify specific characteristics for non-invasive, automatic selection of fruit with sunburn, the effect of sunburn on external and internal features on sunlit and shaded fruit sides was assessed in ‘Granny Smith’, ‘Fuji’ and ‘Braeburn’ cultivars. It has been shown that shaded sides of apple with and without sunburn generally do not differ in their internal fruit quality characteristics, Lab colour readings and chlorophyll fluorescence intensities. With sunlit fruit sides, sunburn induced changes in Lab values are cultivar specific. The common feature of fruit with sunburn in all tested cultivars is a greater difference between fruit firmness and soluble solids content on shaded and sunlit sides as compared to unaffected fruit. Due to the chlorophyll breakdown in the affected areas, laser-induced chlorophyll fluorescence (LIF) is proposed as an appropriate sensitive technique for the reliable sunburn detection in green and red apple cultivars.

► We studied the effect of sunburn browning on fruit quality characteristics in three apple cultivars.
► Changes in Lab colour readings in response to sunburn are cultivar specific.
► Sunburn injury is accompanied by increased fruit firmness and soluble solids content and chlorophyll breakdown.
► Laser-induced fluorescence is a reliable method for detection of sunburn in apple.