Non-destructive measurement of acidity, soluble solids, and firmness of Jonagold apples using NIR-spectroscopy

In this study the potential of visible and near infrared spectroscopy (380-1650 nm) as a nan-destructive measurement technique for measuring quality characteristics of Jonagold apples is evaluated. A relation has been established between the reflectance spectra recorded with a bifurcated optical fibre and fruit parameters such as the pH, the soluble solids content, the stiffness factor and other texture parameters such as the elastic modulus of the flesh. The data were analyzed with multivariate calibration techniques such as principal component analysis (PCA), principal component regression (PCR) and partial least squares analysis (PLS). The impact of the data preprocessing on the prediction performance has also been investigated. The prediction models indicate a good to excellent prediction performance. The best pH model has a standard error of prediction (SEP) of 0.068 and a correlation between predicted and measured values (r) of 0.93. The proposed model for the stiffness factor has a SEP of 2.49 and an r-value of 0.90. For the soluble solids content model a SEP of 0.61 and an r-value of 0.82 is obtained. it has been shown that the pH model has a physico-chemical background. The prediction performance of the model for the elastic modulus, however; was not yet satisfactory (SEP = 0.26 r = 0.75).