NONDESTRUCTIVE 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 h as been established between the reflectance spectra recorded with a bi furcated optical fibre and fruit parameters such as the pH, the solubl e solids content, the stiffness factor and other texture parameters su ch as the elastic modulus of the flesh. The data were analyzed with mu ltivariate 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 predictio n performance has also been investigated. The prediction models indica te 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 so luble solids content model a SEP of 0.61 and an r-value of 0.82 is obt ained. it has been shown that the pH model has a physico-chemical back ground. The prediction performance of the model for the elastic modulu s, however; was not yet satisfactory (SEP = 0.26 r = 0.75).