A validated stability-indicating HPLC with photodiode array detector (PDA) method for the stress tests of Monascus purpureus-fermented rice, red yeast rice

A stability-indicating reversed phase high-performance liquid chromatography (RP-HPLC) with photodiode array (PDA) detection method was developed and validated for the assay of monacolin series compounds including monacolin K, L, J and their hydroxyl acid forms as well as dehydroxymonacolin K simultaneously in Monascus purpureus-fermented rice, red yeast rice. Well-resolved peaks of seven main compounds of monacolin family were profiled on a C18 reverse-phase column using a linear gradient of 0.1% trifluoroacetic acid and acetonitrile as the mobile phase, and the detection wavelength was set at 237 nm. The method was validated with respect to specificity, chromatographic parameters, linearity, precision, accuracy, limits of detection and quantitation. The stability stress testing for fermented red yeast rice powder was carried out to show the effects of high temperature (80 °C), high humidity at room temperature (92.5% RH, 25 °C), high humidity at high temperature (75% RH, 60 °C) and light (sunlight) in solid state. The results exhibited that monacolins decreased significantly under the conditions of high humidity at high temperature (75% RH, 60 °C) and sunlight. Monacolin K and its hydroxyl acid form would be dehydrolyzed and turned to dehydromonacolin K at high temperature (80 °C) while the monacolin K, J and L would be transformed into their corresponding hydroxyl acid forms under the condition of high humidity (92.5% RH, 25 °C). The indication is that monacolins in red yeast rice powder are light-sensitive and thermal-sensitive. Therefore, it has been suggested that the preparations containing monacolins be stored in the place of cool and lightproof. The proposed degradation pathways were discussed as well. The multi-components assay for stability of botanical products could provide much more information than the normal marker-orientation method.