Comparison of destructive and non-destructive measurements of table grape berries to assess quality parameters using spectroscopy

Abstract

The quality of table grapes is critically influenced by several parameters, including sugar content, acidity, firmness, and overall appearance. Traditional methods for assessing these attributes often involve destructive sampling, which can be labour-intensive and impractical for large-scale analysis. In this study, we compare destructive and non-destructive techniques for evaluating the quality of table grape berries of two table grape cultivars (Crimson Seedless and Sugar CrispTM) in a controlled laboratory setting, focusing on using spectroscopy as a means of measurement. Destructive measurements involved conventional techniques such as sugar content determination (refractometry) and a benchtop commercially calibrated Fourier Transform Mid-Infrared (FT-MIR) spectrometer, which delivers total soluble solids (TSS), titratable acidity (TA), pH, and malic acid (MA) values from small samples (2 mL). For non-destructive measurements, we employed spectral data obtained from four spectrometers: two portable, low-cost spectrometers i.e., NIR-S-G1 and Stellarnet BLACK-comet C-SR, and two benchtop spectrometers i.e., FT-MIR and Solid Probe Multi-Purpose Analyser Fourier Transform Near-infrared (SP-MPA-FT-NIR). The characteristics and accuracy of each method were compared and analysed from samples obtained during the whole ripening period in both cultivars. Results confirmed that the destructive spectroscopic technique was highly reliable for TSS estimations with determination coefficients (R2) and root-mean-square error (RMSE) around 0.97 and 0.83 ºBx for both cultivars during the whole ripening period.  The non-destructive spectroscopy methods presented promising results, with R2 values ranging from 0.72 to 0.88 for all configurations and quality parameters tested in this study. These results demonstrated a high potential of the non-destructive spectroscopy offering a low-cost, faster and more efficient approach for quality assessment facilitating improved fruit selection and quality monitoring of table grapes.