UPLC Multiwavelength Quantification and PLS-DA Reveal Stir-Baking Degree-Dependent Marker Dynamics in Paeoniae Radix...

Paeoniae Radix Alba (PRA, roots of Paeonia lactiflora Pall.) yields stir-baked (sbPRA), charred (cPRA), and carbonized (caPRA) specifications through increasing degrees of stir-baking. In this study, an ultrahigh-performance liquid chromatography (UPLC) method was developed to quantitatively determine seven chemical constituents in 15 batches of PRA with varying degrees of stir-baking. The method showed excellent linearity (R² ≥ 0.9995), with precision RSDs < 2%, repeatability and stability RSDs of 0.93%-2.8% and 0.68%-1.5%, respectively, and mean recoveries of 92.24%-105.9% (RSD < 3%). In caPRA, most constituents were below the detection limit. Oxypaeoniflorin, catechin, paeoniflorin, and benzoylpaeoniflorin decreased progressively with increasing processing intensity, whereas gallic acid increased markedly from PRA to cPRA. The concentrations of albiflorin and 1,2,3,4,6-O-pentagalloylglucose showed an initial increase followed by a decrease, reaching maximum levels in sbPRA. Partial least squares discriminant analysis (PLS-DA) identified gallic acid as a key discriminatory marker. Simulated processing experiments showed that paeoniflorin and benzoylpaeoniflorin could decompose into benzoic acid, while 1,2,3,4,6-O-pentagalloylglucose could degrade into gallic acid. This study compared the content of seven components in PRA subjected to different degrees of stir-baking and clarified their transformation patterns.