A comparative study of reflectance and transmittance modes of Vis/NIR spectroscopy used in determining internal quality attributes in pomegranate fruits

The objective of this study was to compare transmission and reflectance modes of visible (VIS)/near infrared (NIR) spectroscopy for their ability to nondestructively determination of key pomegranate quality attributes such as total soluble solid content (TSS), pH and firmness. Partial least squares (PLS) regression was used to develop calibration models. The reflectance mode predicted TSS with r = 0.95, RMSEC = 0.22 degrees Brix and RPD = 6.7 degrees Brix by calibration models. These parameters for the validation models were found to be: r = 0.94, RMSEP = 0.21 degrees Brix and RPD = 6.72 degrees Brix. The pH was predicted with r = 0.85, RMSEC = 0.068 degrees Brix and RPD = 4.58 degrees Brix for calibration set and r = 0.86, RMSEP = 0.069 degrees Brix and RPD = 4.43 degrees Brix for validation sets by reflectance mode. The results indicated that it was possible to use both the transmission and reflectance modes to develop a system in determination of the internal attributes of pomegranate fruit. However, reflectance mode spectra provided more accurate assessment of TSS, pH and firmness.