Predicting bruise susceptibility of ‘Golden Delicious’ apples using hyperspectral scattering technique

• Hyperspectral scattering was used to predict the bruise susceptibility of apples.
• Bruise volume was estimated from the digital images of the bruised fruit.
• Relative mean reflectance was calculated to predict bruise susceptibility.
• Good prediction results were obtained from the PLS models.

Prediction of the susceptibility of apples to bruising can provide useful information for proper postharvest handling and storage operations. The objective of this research was to develop a nondestructive method for predicting the bruise susceptibility of apples using hyperspectral scattering technique. Spectral scattering images between 500 and 1000 nm were acquired for 300 ‘Golden Delicious’ apples over a time period of three weeks after harvest, using a hyperspectral imaging system. Individual apples were then subjected to impact test by a pendulum ball at one of the three levels of impact energy, i.e., 1.11, 0.66, and 0.33 J. Relative mean reflectance was computed for the scattering profile of each wavelength over 10 mm scattering distance. Bruise volumes were estimated from the digital images of the bruised fruit, using a bruise volume estimation model. The bruise susceptibility of apples, determined as the ratio of bruise volume to impact energy, ranged between 353 and 881 mm3 J−1 for the test apples. Bruise susceptibility was affected by the level of impact energy; higher bruise susceptibility values were obtained at low impact energy. Partial least squares (PLS) models for bruise susceptibility were developed for each impact energy level as well as for the pooled data. Better predictions of bruise susceptibility were obtained from the PLS models for each impact energy level, with the correlation coefficient of prediction or Rp = 0.848–0.919 and root mean square error of prediction or RMSEP = 32.4–50.7 mm3 J−1. Lower prediction results were obtained for the pooled data (Rp = 0.826 and RMSEP = 69.7 mm3 J−1). This research demonstrated that hyperspectral scattering can be used for evaluating the bruise susceptibility of apples, which would be useful for postharvest handling of fruit.