# Hyperspectral Imaging as a Rapid Quality Control Method for Herbal Tea Blends
## 4 Conclusions  
A holistic quality control approach which is particularly important in the herbal products industry has been previously demonstrated by several researchers. The non-destructive differentiation of raw materials/species to ensure the authenticity of raw material included in herbal products has been investigated [13; 22; 26]. Quantitatively, although not as accurately as other conventional techniques such as chromatography, adulteration has been successfully detected in commercial products using this technique [30; 31]. As far as herbal teas are concerned, the use of HSI in their quality control is fairly new with only a few studies documented. [PERSON] et al. [23] reported on the successful application of HSI using visible light for the classification of different Chinese teas namely; China black, Lung Ching, Tikuanyin, Yunnan and Jasmine. In another study, different grades of green tea were qualitatively assessed using NIR hyperspectral imaging spectroscopy [32]. It is clear that there is promise in the use of HSI for quality control, mostly due to the rising popularity in herbal tea consumption, existence of various brands of different qualities, varying prices and more recently the introduction of tea blending. The three examples discussed demonstrated the application of HSI in the differentiation of raw materials and their subsequent identification in tea bag blends. With the aid of powerful chemometric algorithms it was possible to quantitatively determine the proportion of each raw material constituent by simply scanning a tea bag and introducing the image into the PLS-DA calibration model. The robustness of these models was demonstrated by the accuracy of predicting replicates. As HSI does not require sample preparation, all the tea bags were analyzed intact and this did not compromise the prediction results. These results show how spatial information is retained, something not possible with conventional methods of analysis. Although UHPLC-MS is a popular method for quality control, the need for sample preparation and targeting of marker constituents to ensure the identity of a raw material is expensive, and requires standards and skilled personnel. Method optimization for each tea/species is a complex process which requires time. Using HSI, this was not necessary as all the species could be analyzed using the same instrumental parameters. Quantitative determinations in chromatography are always a drawback as most standards for targeted analysis are not readily available for herbal products. Vibrational spectroscopy has the advantage of not requiring standards to confirm the identity of a particular component since the whole spectral signature is used. The greatest analytical challenge in the quality control of herbal tea bag blends is the complexity. Often several species are combined in the tea bag formulation, which implies that diverse chemistries are superimposed in the consumer product. Due to  
Figure 9: (**a**) UHPLC-MS-ES\({}^{-}\) chromatograms showing the marker compound aspalathin (\(Rt\) = 5.43 min) identified in rooibos and (**b**) the marker SU1 (\(Rt\) = 10.80 min) identified in cancer bush raw material, and (**c**) the two marker compounds in the tea bag blend. this complexity, a single UHPLC method may not be sufficient to identify unique biomarkers, implying that one formulation would need to be analyzed on different analytical platforms using different chromatographic parameters. Furthermore, although the identification of biomarkers can confirm the presence of a species, it cannot provide information on the proportion of each species in the blend. All these factors make HSI a favorable tool in quality control systems where short turnaround times are of particular importance, and in the herbal products industry, where standards are not readily available and specifications not clearly documented. The authors would like to thank [PERSON] from Rooibos Limited (Clanwilliam, South Africa) for providing the raw materials and tea bag blends.