Nondestructive determination of dry matter and soluble solids content in dehydrator onions and garlic using a handheld visible and near infrared instrument

- VIS-NIR spectroscopy was studied on garlic and onion using a handheld spectrometer.
- VIS-NIR wavelengths were used to predict dry matter and soluble solid content.
- The model based on relative wavelengths provided the best prediction accuracy.

A non-destructive method based on visible and near- infrared spectroscopy was investigated for determining the dry matter and soluble solids contents of dehydrator onions (485 samples) at the base, equatorial, and shoulder locations and of garlic cloves (270 samples) at the equatorial location. The interactance spectrum (400-1000 nm) of each sample was measured non-destructively within a 5 s period using a handheld spectrometer that employed an optical design of 0° angle between the incident illumination and the detection view. The spectral data were used to develop partial least square regression models to predict the dry matter and soluble solids contents. The results showed that the predictive performance of the onion model with optical measurements taken at the equator and shoulder locations were superior to the performance at the base location. For dry matter and soluble solids contents, the onion model performance had coefficient of determination (R2) values of 0.96 and 0.97, with RMSECV values of 1.29 and 1.23, respectively. Similarly, for garlic models, the R2 values were 0.87 and 0.72, with RMSECV values of 1.14 and 1.09, for dry matter and soluble solids contents respectively. These results suggested that the handheld instrument has excellent potential to aid in onion and garlic production processing as a rapid, non-destructive technique to identify the dry matter and soluble solids contents in the field or in an industrial setting.