Optical detection of bruises and early frost damage on apples

Diffuse reflectance in the 400 to 1012 nanometer (nm) region was measured on blemished and nonblemished areas of whole 'Empire' apples. The 'Empire' variety is a multi-colored fruit with a high percentage of green coloration in addition to red pigmentation. Reflectance models were developed from the reflectance spectra for identifying bruised, frost damaged (russett-like appearance) and nonblemished areas on unpeeled apples. Single term linear regression analysis was used to select the proper wavelengths for each model. Models were formed from 96 spectra, which included the reflectance spectra from nonblemished red and green, bruised red and green, and early frost damaged sites. No single model tested could classify the samples into three categories: frost damaged, bruised, and nonblemished. Although the ratio between the reflectance at two wavelengths had a high correlation (r2 = 0.77), it was unable to separate the nonblemished and bruised green samples from the frost damaged samples. However, a three-step process, based on a different model for each step separated frost damaged fruit from the lot, separated red and green from the remaining areas, and then identified the bruised areas within the red and green samples.