Assessment of firmness and soluble solids content of peaches by spatially resolved spectroscopy with a spectral difference technique

•A new method of calculating spectral differences was proposed to enhance quality predictions.•Firmness and SSC predictions for SR spectra varied with the source-detector distance.•IT spectra gave consistently better results for both firmness and SSC predictions than SR spectra.•IT spectra can make SSC prediction less sensitive to the light scattering effect.