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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Plant Sci. | doi: 10.3389/fpls.2019.01517

Measuring internal maturity parameters contactless on intact table grape bunches using NIR spectroscopy

  • 1Stellenbosch University, South Africa

The determination of internal maturity parameters of table grape is usually done destructively using manual methods that are time-consuming. The possibility was investigated to determine whether key fruit attributes, namely total soluble solids (TSS); titratable acidity (TA), TSS/TA, pH, and BrimA (TSS – k x TA) could be determined on intact table grape bunches using Fourier transform near-infrared (FT-NIR) spectroscopy and a contactless measurement mode. Partial Least Squares (PLS) regression models were developed for the maturity and sensory quality parameters using grapes obtained from two consecutive harvest seasons. Statistical indicators used to evaluate the models were the number of latent variables (LVs) used to build the model, the prediction correlation coefficient (R2p) and root mean square error of prediction (RMSEP). For the respective parameters TSS, TA, TSS/TA, pH and BrimA the LVs were 21, 23, 5, 7 and 24, the R2p = 0.71, 0.33, 0.57, 0.28 and 0.77 and the RMSEP = 1.52, 1.09, 7.83, 0.14 and 1.80. TSS performed best when moving smoothing windows (MSW) + multiplicative scatter correction (MSC) was used as spectral pre-processing technique, TA with standard normal variate (SNV), TSS/TA with Savitzky-Golay first derivative (SG1d), pH with SG1d and BrimA with MSC. This study provides the first steps towards a completely non-destructive and contactless determination of internal maturity parameters of intact table grape bunches.

Keywords: Table grapes, Contactless scanning method, near-infrared spectroscopy, sensory quality, Total soluble solids (TSS), Titratable acidity (TA), Sugar/acid ratio, pH, BrimA

Received: 24 Jun 2019; Accepted: 31 Oct 2019.

Copyright: © 2019 Daniels, Nieuwoudt, Opara and Poblete-Echeverría. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Dr. Hélène Nieuwoudt, Stellenbosch University, Stellenbosch, South Africa, hhn@sun.ac.za
Prof. Umezuruike L. Opara, Stellenbosch University, Stellenbosch, South Africa, opara@sun.ac.za