Qualitative and quantitative analysis of major components in Abelmoschus manihot flowers treated with different drying methods using UHPLC Q-exactive MS and HPLC-PDA

The flowers of Abelmoschus manihot (L.) Medic are commonly used in clinical practice in China to cure forms of chronic kidney disease. Despite a long history of traditional use, the flowers obtained by different drying technologies have never been fully chemically characterized, and the ranges of constituents between different drying methods have not been comprehensively reported. To establish a quality control and chemical characterization method, a total of 14 batches of samples corresponding to 14 postharvest treatments were studied. Seven flavonoids were quantified using a HPLC-PDA method. The method was validated in terms of linearity (r > 0.999), precision (intra- and inter-day: 0.7-1.4 %), accuracy (99.90-100.7 %), detection limit (0.34-0.46 µg/mL) and quantification limit (1.15-1.52 µg/mL). The contents of total flavonoids in manihot flowers were as follows in descending order: Infrared Drying (50.96 mg/g) > Microwave Drying (41.84 mg/g) ≈ Hot-air Drying (39.58 mg/g) ≈ Fresh (39.35 mg/g) ≈ Primary Drying (38.95 mg/g). Principal component analysis showed that samples processed with Fresh, Primary Drying, and the investigated three modern drying methods were well classified into three domains, indicating an important difference between drying methods. For the purpose of saving the flavonoids contents, infrared drying under 80-100 °C would be most acceptable. Furthermore, using UHPLC Q-Exactive Orbitrap MS data with targeted and non-targeted approaches, 28 compounds were identified in Abelmoschus manihot samples. Flavonoids were the main group of compounds found in Abelmoschus manihot flowers. The study could provide the scientific evidence for the selection and optimization of appropriate drying method for manihot flowers, and also provide the reference for the formation of generic primary drying processing technology for medicinal flowers containing flavonoids.