Rapid non-destructive moisture content monitoring using a handheld portable Vis–NIR spectrophotometer during solar drying of mangoes ( Mangifera indica L.)

The aim of the present work was to determine the efficacy of handheld portable Vis–NIR spectroscopy in rapid non-destructive moisture content monitoring during the solar drying of mangoes. Mango slices (1.5 cm thick) from five (5) commercial mango cultivars and two breeding selections were pre-treated by hot water blanching, dipping in distilled water (control); sodium metabisulphite and citric acid solutions. Vis–NIR absorbance spectra in the range of 474–1047 nm (191 spectra points) of the samples were recorded during solar drying at temperatures of 16.8–54.3 °C and relative humidity of 19.2–99.3%. A training set consisting of 168 spectra was utilized to develop models based on partial least squares regression. Chemometric analysis gave an optimum wavelength range model that could explain 95.2% of the variance in the moisture content with a detection limit of 5.39%. The optimum model was tested for prediction of the moisture content based on 72 spectra from similarly treated samples. The model could explain 91.6–98.7% of the variance in the moisture content of the test samples with detection limits ranging from 3.97–6.61% w/w. The research demonstrated that portable hand-held Vis–NIR spectroscopy was a robust and effective method for rapid non-destructive monitoring of moisture during solar drying of mangoes. Non-destructive hand-held portable Vis–NIR spectrophotometers can hence facilitate the production of high quality solar dried mangoes.