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

  • Obiro Cuthbert WokadalaEmail author
  • Christo Human
  • Salomie Willemse
  • Naushad Mohammad Emmambux
Original Paper


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.


Solar drying Chemometrics Vis–NIR spectroscopy Mango Moisture content Rapid non-destructive methods 



The authors are grateful to Ms. Karen de Jager for assistance with the solar dryers and the University of Venda students; Cenolia Mgomezulu, and Ntsako Mkhabela for assistance with solar drying trials. The authors are also grateful to T. Malindi and A. Zikhali for general technical assistance.


This work was supported by the University of Pretoria NRF Smart Foods Project, Project Number 170206.

Compliance with ethical standards

Conflict of interest:

All the authors have no conflict of interest to declare.


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Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Postharvest Technologies DivisionAgricultural Research Council, Tropical and Subtropical CropsNelspruitSouth Africa
  2. 2.Department of Consumer and Food SciencesUniversity of PretoriaHatfieldSouth Africa

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