Standardization and Quality Control of Herbal Medicinal Products – Does Vibrational Spectroscopy Offer the Solution?

It is a well-known fact that 80% of the world's population use herbal medicines. The herbal medicines market has increased dramatically in recent years, as consumers became more health conscious, herbal medicines are considered safe by consumers and these products are generally less expensive than allopathic medicines. These products are however not rigorously regulated and quality and safety cannot be guaranteed. In fact, many cases of toxicity have been reported, in some cases due to errors in species identification that is, or should be, one of the first steps in an herbal quality control protocol. Established, methodical processes are necessary to standardize herbal medicines to produce consistent and reproducible products. Herbal medicines pose significant standardization and quality control challenges due to their innate phytochemical complexity and intraspecies variability. Standardization and quality control involves inter alia the authentication of plants followed by the quantification of identified biomarkers and the selection and cultivation of the chemotype with the desired characteristics (e.g. ratios of biomarkers). Vibrational spectroscopy has been identified and implemented as an important quality control technique in the pharmaceutical, food and beverage and agricultural industries. The technique has gained popularity as it is non-destructive, inexpensive, and any sample matrix (powder, liquid, essential oils) can be tested with minimal or no sample preparation. Therefore, no bias is introduced as a result of using different extraction solvents and the entire metabolome is used. The large datasets obtained using vibrational spectroscopy (NIR, MIR and hyperspectral imaging) are analyzed using chemometric data analysis. This allows for species authentication using discrimination models constructed using the Orthogonal Projections to Latent Structures (OPLS) technique. In combination with data obtained from standard analytical methods (e.g. LC-MS), calibration models that correlates the information in the spectral data to the chemical or reference data was used to quantify biomarkers. In addition, cluster formation during exploratory principle component analysis supplies valuable information through the detection of similarities between samples. This may be used in conjunction with hierarchical cluster analysis to identify and suggest the best chemotype to cultivate. Several examples related to quality control and standardization of medicinally and commercially important plant species will be discussed: Species authentication and/or biomarker quantification (Agathosma, Harpagophytum, Illicium and Pelargonium species); chemotype selection (Sceletium tortuosum).