The effect of different drying methods on non-volatile and volatile components and immunomodulatory activity of Osmamthus fragrans flowers

Background: Osmamthus fragrans (O. fragrans) has high ornamental, edible and medicinal value in China. The components of its flowers have been gradually revealed, but the active ingredients with immunoregulatory activity have been unknown. Also, it needs to be studied that which groups and drying methods can make O. fragrans fowers produce more immunomodulatory activity. This study aimed to investigate the effects of drying methods on non-volatile and volatile components of O. fragrans flowers from three groups, and to further explore if their groups and drying methods had an ovious effect on their immunoregulatory activity.Methods: O. fragrans flowers from three groups such as “Aurantiacus”, “Latifolius” and “Thunbergii” were dried with shade drying, sun drying, quick-lime drying, oven drying and microwave drying method, respectively. The non-volatile components such as salidroside, verbascoside, oleanolic acid and ursolic acid and volatile components such as linalool, linalool oxide, geraniol, α-ionone and β-ionone of O. fragrans flowers above were determined by high-performance liquid chromatography (HPLC) and gas chromatography (GC), respectively. The immunomodulatory activities of chemical components above were investigated by the neutral red uptake assay.Results: There are more non-volatile components and less volatile components in O. fragrans flowers from Aurantiacus group and Latifolius group than Thunbergii group. Microwave drying and oven drying at high temperature were beneficial for the preservation of the bioactive non-volatile components for killing enzyme and protecting glycoside. Other drying methods such as shade drying, sun drying, quick-lime drying and oven drying at low temperature were beneficial to their preservation of the fragrant volatile components. Salidroside, verbascoside, linalool, and linalool oxide had the better immunoregulatory activity than other ingredients. In addition, non-volatile components played a more important role in the contribution to the immunoregulatory activity than the volatile components as the former was almost 1000 times as much as the latter. Conclusions: O. fragrans flowers from Aurantiacus group with microwave drying (high fire) method had the best immunoregulatory activity. The research could provide some evidence in choosing drying method of O. fragrans flowers as food or medicine.