Aquaphotomics study of fresh cannabis inflorescence: near infrared spectral analysis of water matrix structures

Abstract

Aquaphotomics is an approach that describes the water-light interactions in aqueous solutions or biological systems and retrieves information about the nature of the underlying water-related interactions. We evaluated the water spectral pattern (WASP) and water matrix structure of freshly harvested cannabis inflorescence from seven different chemovars using near-infrared (NIR) spectral data coupled with chemometric models. Six activated water bands-1342, 1364, 1384, 1412, 1440, and 1462 nm, occurred consistently in all of the spectrum exploration steps as well as in the partial least squares-discriminant analysis (PLS-DA) steps. However, according to major class and chemovar aquagram values, the largest spectral variation was associated with the following bands: 1412, 1364, 1374, 1384, 1488, and 1512 nm. A strong positive correlation between 1364, 1374, and 1384 nm aquagram values and a strong negative correlation between 1412 and 1512 nm aquagram values were observed through all aquagram analysis steps. These water activated bands were found to serve as good discriminators and classifiers according to either major class or chemovar. Furthermore, significant differences in the water matrix structure of different cannabis chemovars were observed, with the highest variations associated with the presence of free water molecules, small molecule solvation shells, extent of strongly bound water, and the number of hydrogen bonds per water molecule. Minor cannabinoids and terpenes such as cannabigerolic acid and (-)-guaiol displayed relatively high correlations with these bands. The results of this study suggest that the most accurate way to explore the cannabis inflorescence water matrix spectral pattern is by chemovars and not by major classes.

Keywords: Aquaphotomics; Fourier transform near-infrared spectroscopy (FT-NIR); Water spectral pattern (WASP); Wet Cannabis sativa L. inflorescence.

Fig. 1

FT-NIR raw reflectance spectra in the wavelength region of 1300–1600 nm of the complete set of samples labeled according to a major classes and d chemovars. Additionally, b the mean spectra and c standard deviation of the different major classes and e the mean spectra and f standard deviation of the different chemovars are provided

Fig. 2

Preprocessed FT-NIR reflectance spectra using 2nd derivative followed by MSC and smoothing in the wavelength region 1300–1600 nm of a the complete set of samples and the mean preprocessed FT-NIR reflectance spectra of b major classes and c chemovars

Fig. 3

a LV loadings and b regression vectors plots of major class PLS-DA classification model and c LV loadings and d regression vectors plots of chemovar PLS-DA classification model. The dashed grey lines represents the 12 different activated water bands in the first overtone region of the OH stretching ban

Fig. 4

Aquagrams of the OH first overtone 12 WAMACS of a major classes and b chemovars

Fig. 5

PCA analysis of the OH first overtone 12 WAMACS values. Major classes first two PCs a score and b loading and chemovars first two PCs c score and d loading plots