Characterization and simultaneous determination of immunosuppressive decalins in red yeast rice by ultra-high-performance liquid chromatography hyphenated with mass spectrometry

• First time report the MS fragmentation patterns of immunosuppressive decalins.
• A new decalin was identified by the established MS spectrum interpretation.
• A simultaneously quantitative method for decalins was firstly established.
• Innovatively discovered that decalins only exist in functional red yeast rice.

Decalins are secondary metabolites of red yeast rice with immunosuppressive effects on human T cell proliferation. In this study, ultra-high-performance liquid chromatography hyphenated with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) was employed for elucidation of the mass fragmentation patterns of decalins by collision-induced dissociation tandem mass spectrometry (CID-MS/MS). Based on the MS/MS fragmentation patterns of the authentic decalin standards as well as high mass accuracy, a new decalin in the crude extract of red yeast rice was further putatively identified. Moreover, a quantitative analysis method of five immunosuppressive decalins by ultra-high-performance liquid chromatography hyphenated with triple quadrupole tandem mass spectrometry (UHPLC–QQQ-MS) under multiple reaction monitoring (MRM) mode was developed and validated. This method exhibits limits of detection from 0.44 to 1.96 mg/kg, and precision variations were less than 3.2%, and the recovery was in the range of 82 and 105% with RSD less than 5.4%. This method was successfully applied in the quantitative analysis of decalins in different types of red yeast rice. The results showed that decalins only exist in functional red yeast rice but not in the common one. The study demonstrated that UHPLC-Q-TOF-MS and UHPLC–QQQ-MS methods described in this paper are powerful and reliable tools for the quality control of red yeast rice.