Investigating the Thermal Transformations of Chlorogenic Acids During Dry-Heating Processing of Lonicerae Japonicae...

Lonicerae japonicae Flos (LjF, honeysuckle) is a major component of beverages and healthcare products, as well as a key botanical resource in traditional Chinese medicine. Chlorogenic acids (CGAs) are the main bioactive components of LjF, possessing antioxidant, anti-inflammatory, antiviral, and other biological activities, among which CGA serves as the key marker compound for LjF quality evaluation. In the present work, LjF samples were subjected to controlled dry heating and analyzed by LC-DAD and UPLC-QTOF-MS. Progressive degradation of neochlorogenic acid, cryptochlorogenic acid, and isochlorogenic acid A was accompanied by concomitant accumulation of CGA, isochlorogenic acid B, and isochlorogenic acid C. Furthermore, the effects of temperature and time on thermal transformation, along with key chemical markers for different heat treatment conditions were clarified via principal component analysis of chemical changes. Mechanistic investigations revealed that isochlorogenic acid A undergoes competitive cleavage of the C-3 or C-5 caffeoyl ester bond to yield neochlorogenic acid (kinetic product) or CGA (thermodynamic product), followed by intramolecular acyl migration to form isochlorogenic acid B and isochlorogenic acid C, with isochlorogenic acid C identified as the most stable dicaffeoyl isomer. The interconversion of monocaffeoyl isomers leads to a dynamic equilibrium, with CGA being the predominant and most stable form. These results provide the comprehensive thermal-transformation map for CGAs in LjF and offer practical guidance for optimizing drying, roasting, and extraction protocols in the development of high-quality LjF, an edible and medicinal homologous resource.