The quality control of two Pueraria species using Raman spectroscopy coupled with partial least squares analysis

The dried roots of Pueraria lobata (Puerariae Lobatae Radix; PLR) and Pueraria thomsonii (Puerariae Thomsonii Radix; PTR) are medicinal herbs that are used interchangeably in clinical practice, even though their chemical profiles are different. Therefore, the aim of this study was to develop a rapid and non-destructive method for the quality control of Pueraria species using Raman spectroscopy in combination with partial least squares analysis. Partial least squares-discriminant analysis (PLS-DA) was used to differentiate PLR from PTR, whereas partial least squares regression (PLSR) was used to predict the total phenolic content (TPC) and antioxidant capacities of the Pueraria species. Raman spectroscopy revealed that spectral characteristics of starch and polyphenols differentiated the two species, with the PLS-DA model giving 100% classification accuracy for the tested samples. A significantly higher TPC (p < 0.001), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity (p < 0.001) and cupric reducing antioxidant capacity (CUPRAC; p < 0.001) were observed for PLR as compared to PTR. The high ratio of performance to deviation values (TPC: 9.84; ABTS: 7.11; CUPRAC: 7.13) indicated the PLSR models were robust for predicting TPC and antioxidant capacities. The loading plot revealed that the content of starch and polyphenols were important factors in differentiating PLR from PTR and predicting TPC and antioxidant capacities. The results demonstrate that Raman spectroscopy coupled with chemometrics is a rapid method for the quality control of PLR and PTR. These methods can be applied as a template for the quality control of other herbal medicines and products to promote the correct identification of herbs for clinical practice.