Rapid screening methods for estimation of mangiferin and xanthone contents of Cyclopia subternata plant material

Two rapid screening methods, i.e. a colorimetric method employing aluminium chloride complexation and near infrared (NIR) spectroscopy, were evaluated for prediction of the mangiferin and xanthone contents of unfermented Cyclopia subternata plant material. Optimum analytical extraction conditions in terms of solvent and time for mangiferin were determined to ensure accurate HPLC reference data. The AlCl3 colorimetric method gave moderate prediction of the mangiferin content (y = 1.3x + 0.87; R2 = 0.55). The NIR spectroscopy calibration models developed for prediction of mangiferin (SEP = 0.21 g/100 g; R2 = 0.67) and xanthone (SEP = 0.27 g/100 g; R2 = 0.66) contents are suitable for screening purposes. To improve the robustness of the NIR spectroscopy calibration the model data set were expanded to include data of unfermented Cyclopia genistoides, having higher xanthone content. This did not improve the NIR spectroscopy calibration for prediction of C. subternata samples, although the calibration was more robust for prediction of C. genistoides samples. Using principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA) it was possible to clearly differentiate between the two species.