Internal bruise damage in machine-harvested blueberries

This paper describes the relationship between bruise damage and fruit firmness in mechanically impacted blueberries before and after sorting. To create mechanical impact damage in the fruit, blueberries were dropped on a rigid plastic plate. A novel, hyperspectral imaging (HSI) system was employed as a non-destructive method to locate and quantify internal bruise damage. A reflective HSI system distinguished the bruised area from non-bruised area in the fruit and a deep learning web-based application quickly determined the blueberry bruise levels. A FirmTech II instrument measured fruit firmness at the impacted area. The fruit was then rotated 90 and 180° from the bruised area for two additional measurements. A visual method (e.g., slicing the fruit through the equatorial axis) verified the bruise damage. FirmTech II measurements indicated that fruit firmness was significantly lower at the impacted zone compared to the 90 and 180° rotated fruit locations. In a separate study, machine-harvested blueberries were cold stored for three weeks and analyzed for firmness and internal bruise damage. The linear regression between the bruise area predicted by the non-destructive HSI system and the destructive visual method was highly correlated. The correlation between the bruise size and fruit firmness was weak. The combination of these methods and innovative technologies such as hyperspectral imaging will enable blueberry breeders, growers, and packers to rapidly evaluate berry internal bruises created by mechanical harvesters.