Predicting the Soluble Solids Concentration and Acid Ascorbic of Intact Jackfruit var. Tekam Yellow Using Visible Near Infrared Spectroscopy: Effect of Rind and Flesh

The Malaysian jackfruit ( Artocarpus heterophyllus cv. Tekam Yellow) industry faces a major challenge from jackfruit bronzing , a physiological disorder caused by Pantoea stewartii subsp. stewartii . The disease induces internal discoloration of the flesh and rag from yellowish-orange to reddish hues, while the rind remains visually unaffected, hindering early detection and reducing market value. This study assessed the potential of visible–near infrared spectroscopy (Vis–NIRS) as a non-destructive diagnostic tool for detecting internal bronzing through rind spectral analysis at 10, 12, and 14 weeks after anthesis (WAA). Twenty-seven syncarps were sampled, and reflectance spectra (500–950 nm) from 30 rind sections per fruit were recorded using an Ocean Optics HR4000 spectrometer. Partial Least Squares Regression (PLSR) models were developed to predict soluble solids concentration (SSC) and ascorbic acid (AA) using pre-processed spectra (Savitzky–Golay smoothing, Standard Normal Variate, and Multiplicative Scatter Correction). The optimal models achieved high validation performance with Rv² values of 0.94–0.97 and RMSEV of 1.26–1.67% for SSC and 0.72–1.59 mg/100 g FW for AA. Reference analyses indicated mean SSC values of 4.38%, 9.09%, and 10.01%, and AA contents of 18.98, 19.95, and 12.24 mg/100 g FW at 10, 12, and 14 WAA, respectively. ANOVA and Fisher’s LSD (p ≤ 0.05) confirmed significant variations across maturity stages and disease conditions. These findings demonstrate that Vis–NIRS integrated with chemometric modeling provides a rapid, accurate, and non-invasive method for early bronzing detection and quality assessment in jackfruit supply chains.