Portable NIR Spectroscopy-Chemometric Identification of Chemically Differentiated Yerba Mate (Ilex paraguariensis) Clones

Yerba mate plants are part of the ombrophilous mixed forest with araucaria trees. Genetically improved yerba mate clones are classified into two groups of interest to a selective consumer public, decaffeinated and high caffeine plants. Quality control strategies for this type of food are essential, and multivariate tools can help in this procedure. Partial least squares-discriminant analysis (PLS-DA) was used to identify chemically differentiated yerba mate plants together with reflectance measurement (900-1700 nm) near-infrared spectroscopy (NIRS) in direct analysis of plant material. Yerba mate plants were cultivated in the semi-hydroponic system under five plant shading levels (0%, 40%, 51%, 76%, and 82%). Robustness of the mathematical model was verified for plants with all these shading levels. The PLS-DA model showed a sensitivity of 96.52% for the training set and 93.33% for the test set. Specificity greater than 97.12% was found for both sets, with an efficiency rate of 96.82% for the training set and 95.31% for the test set. Wilcoxon signed classification, sign classification in pairs, and randomization t-tests showed an excellent model fit. Principal component analysis of the NIR spectra demonstrated that shading affected the chemical composition more in high-caffeine clones than in decaffeinated ones. This indicates that the caffeine synthesis in yerba mate plants represents an adaptative strategy to elevated light conditions.

Automated summary

In this study, chemically differentiated shade-tolerant and high-caffeine yerba mate clones were analyzed using near-infrared spectroscopy and partial least squares-discriminant analysis. The results showed that high-caffeine clones were more sensitive to shading, indicating that caffeine synthesis is an adaptive strategy to low-light conditions.