Robust method for the analysis of monacolin K in red yeast rice

Red yeast rice (RYR) is produced by the fermentation of rice with Monascus species. During fermentation a variety of secondary metabolites are formed: pigments, citrinin, monacolin K and others. In Asia, the use of RYR in food and as a medicine exists for over of thousands years. More recently, RYR products are described in scientific reports mainly for the management of blood cholesterol. For companies providing food supplements with RYR, it is very important to control the quality of the RYR bulk product that is mostly produced in China. The extraction and analysis of monacolin K and lovastatin from RYR powder was already described in previous articles [1, 2]. However, by analyzing RYR bulk products, we experienced problems related to the robustness of the methods. Causes we identified were incompleteness of extraction and pH dependent transitions. A robust analytical method using reversed phase high-performance liquid chromatography (RP-HPLC) with diode array detection (DAD) was developed and validated for the quantification of lovastatin and monacolin K in RYR bulk products. Tests on the composition of the extraction solvent to minimize transition, the time of extraction and the number of repetitions of extraction were evaluated. Monacolin K, lovastatin and minor monacolin peaks were separated on a C18 column (250 × 4.6 mm, 5 µm) using acetonitrile (ACN)/0.1% trifluoroacetic acid (TFA) as mobile phase. The standard lovastatin curve is linear over a concentration range of 6 – 119 µg/mL. The recovery of the method is 98.75%. The precision of the method with respect to time and concentration is acceptable, with relative standard deviation (RSD%) values of less than 5%.

References:

[1] Li YG, Liu H, Wang ZT. A validated stability-indicating HPLC with photodiode array detector (PDA) method for the stress tests of Monascus purpureus – fermented rice, red yeast rice. J Pharm Biomed Anal 2005; 39: 82 – 90

[2] Wu CL et al. Synchronous high-performance liquid chromatography with a photodiode array detector and mass spectrometry for the determination of citrinin, monascin, ankaflavin, and the lactone and acid forms of monacolin K in red mold rice. J AOAC Int 2011; 94: 179 – 190