Non-destructive and rapid tools are required for predicting the optimum harvest window and for monitoring fruit quality during postharvest period. This study tested a portable, experimental visible/near-infrared (vis/NIR) spectrophotometer, more versatile and handy than traditional vis/NIR instruments, to measure phytonutrients active in human health and important in fruit storability. Parameters determining sensorial and quality properties of the fruit were also analyzed. The vis/NIR measurement was carried out in field using apples of “Golden Delicious” and “Stark Red Delicious” on tree. Calibration models were developed using PLS regression based on second derivative spectra. For “Golden Delicious” apple, the cross-validation R2 for soluble solids content (SSC), chlorophyll, titratable acidity (TA), flesh firmness, total phenols, carotenoids, and ascorbic acid were 0.72, 0.86, 0.52, 0.44, 0.09, 0.77, and 0.50, respectively. The corresponding RMSECV were 0.78 °Brix, 0.50 nmol/cm2, 0.59 g/L, 6.08 N, 0.10 mg/g, 0.08 nmol/cm2, and 0.83 mg/100 g, respectively. For “Stark Red Delicious” similar calibration statistics were found for SSC, TA, flesh firmness, chlorophyll, and ascorbic acid content. A better calibration performance was achieved for total phenols, while for carotenoids it was less accurate. Cross-validation R2 for “Stark Red Delicious” total anthocyanins, total flavonoids, and non-anthocyanic flavonoids were 0.67, 0.86, and 0.77, respectively. The corresponding RMSECV were 0.12, 0.14, and 0.15 mg/g, respectively. It was concluded that the portable vis/NIR instrument performed similarly to bench top or portable vis/NIR instruments reported in the literature.
