Nondestructive Measurement of Soluble Solids Content in Apples by a Portable Fruit Analyzer

Feasibility studies of using a portable fiber spectrometer in conjunction with multivariate and variable screening analysis were investigated for noninvasive inspection of the internal quality of fruit. A highly effective illumination with circular reflective accessories was designed to reflect the divergent light of the lamps onto the sample. The penetrating spectra of the apples were measured for soluble solids content (SSC) at 550 to 985 nm in transmission mode with different numbers of lamps illuminating. The illumination was optimized with six lamps by comparison to the performance of partial least square (PLS) models. Stepwise multiple linear regression (SMLR), genetic algorithm (GA), successive projective algorithm (SPA), uninformative variable elimination (UVE), and their combinations were comparatively employed to screen the important wavelengths and promote the robustness of the calibration model. Finally, the novel calibration model built using UVE-SPA-MLR method on 21 screening wavelengths (only 1 % of all) exhibited higher coefficient of prediction (r (p)) of 0.951 and root mean square error of prediction (RMSEP) of 0.39 % brix for the prediction set. This study shows that the accuracy of the quantitative analysis conducted by the developed analyzer can meet the requirement for practical use.