Assessing Multiple Quality Attributes of Peaches Using Optical Absorption and Scattering Properties

The objective of this research was to measure the spectral absorption (a) and reduced scattering coefficients (s') of peaches, using a hyperspectral imaging-based spatially resolved method, for maturity/quality assessment. A newly developed optical property measuring instrument was used for acquiring hyperspectral reflectance images of 500 'Redstar' peaches. The a and s' spectra for 515 to 1,000 nm were extracted from the spatially resolved reflectance profiles using a diffusion model coupled with an inverse algorithm. The absorption spectra of peach fruit were marked with absorption peaks around 525 nm for anthocyanin, 620 nm for chlorophyll-b, 675 nm for chlorophyll-a, and 970 nm for water, while s' decreased monotonically with the increasing wavelength for most of the tested samples. Both a and s' were correlated with peach firmness, soluble solids content (SSC), and skin and flesh color parameters. Better correlation results for partial least squares models were obtained using the combined values of a and s' (i.e., a s' and eff) than using a or s', where eff is the effective attenuation coefficient: eff = 3a(a + s')1/2. The results were further improved using least squares support vector machine models, with values of the best correlation coefficient for firmness, SSC, skin lightness, and flesh lightness being 0.749 (standard error of prediction or SEP = 17.39 N), 0.504 (SEP = 0.92 Brix), 0.898 (SEP = 3.45), and 0.741 (SEP = 3.27), respectively. These results compared favorably to acoustic and impact firmness measurements, whose correlations with destructive measurements were 0.639 and 0.631, respectively. The hyperspectral imaging-based spatially resolved technique is useful for measuring the optical properties of peach fruit, and it has good potential for assessing fruit maturity/quality attributes.