Non-destructive tests on the prediction of apple fruit flesh firmness and soluble solids content on tree and in shelf life Original Research Article

Acoustic impulse resonance frequency sensor and miniaturized VIS/NIR spectrometer were applied on apple fruit Malus domestica ‘Idared’ and ‘Golden Delicious’ (n = 800) to predict fruit flesh firmness and soluble solids content (SSC) on tree and in shelf life. Partial least-squares calibration models on acoustic data and VIS spectra of ‘Golden Delicious’/‘Idared’ apple fruits on tree were built for predicting the fruit flesh firmness: coefficients of determination (R2) and standard errors of cross-validation (SECV) of R2 = 0.93/0.81 and SECV = 7.73/10.50 [N/cm2] were calculated. SSC prediction of freshly harvested apples using NIR spectrometry was obtained with R2 = 0.20/0.41 and SECV = 1.29/0.94 [°Brix]. Prediction of SSC and fruit flesh firmness of stored ‘Golden Delicious’/‘Idared’ apple fruits showed high errors or was not possible. The fruit maturity stage on tree was predicted as classes based on calendar weeks for ‘Golden Delicious’/‘Idared’ apple fruits with 64%/66% correct classification and 92%/84% correct plus neighboring class with SECV = 0.9/0.9 [weeks]. Classes of ‘Golden Delicious’/‘Idared’ apple fruit at different quality levels due to different storage conditions were non-destructively discriminated with 77%/84% correctly classified fruits and 93%/99% correct plus neighboring class with SECV = 0.8/0.5 [classes]. The results show the potential of non-destructive sensors for predicting accepted fruit parameters enabling the determination of optimum harvest date and fruit quality in shelf life.