2021 FDA Science Forum
Using Carbon Isotope Ratios to Detect Adulteration in Red Yeast Rice Supplements
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Contributing OfficeOffice of Regulatory Affairs
Abstract
Red yeast rice (RYR) is marketed as a dietary supplement as it contains monacolin K, a natural cholesterol-lowering statin. To enhance health claims, there is concern that some RYR supplements could be adulterated with the pharmaceutical drug, lovastatin, a HMG CoA reductase inhibitor (statin). Testing for adulteration in RYR supplements is challenging because monacolin K and lovastatin are chemically identical, but are derived from different sources. Natural abundances of monacolin K in RYR also vary depending on rice type and fermentation conditions. Lovastatin is fermented from the fungus Aspergillus terreus using mostly C4 plant sources (e.g. corn), whereas monacolin K is derived from the mold Monascus purpureus grown on rice, a C3 plant. These two plant groups have unique stable carbon isotope ratios (δ13C) distributions that are inherited in monacolin K/lovastatin. The goal of this study is to build on a recent study demonstrating the isotopic differences between monacolin K and lovastatin to differentiate its sources and to optimize the preparation procedures to isolate monacolin K/lovastatin from the complex RYR supplement matrix. A modified QuEChERS method was used to remove pigments, followed by fraction collecting using high performance liquid chromatography with ultraviolet detection (HPLC-UV). Samples were then analyzed on an Elemental Analyzer-Isotope Ratio Mass Spectrometry (EA-IRMS) for carbon isotopes. To monitor isotope fractionation effects, two lovastatin standards of known δ13C values were analyzed neat then added to two RYR supplements with no monacolin k/lovastatin, extracted, and analyzed. Comparison of δ13C values between treatments showed minimal isotope fractionation. Lovastatin standards (neat) and RYR samples spiked with standards yielded δ13C values (-19.3‰ to -25.8‰) that were isotopically distinct from natural monacolin K δ13C values reported in the literature (-28.2‰ to -30.7‰). Larger ranges in lovastatin δ13C values are attributed to differing amounts of C4 plant material used in the fermentation process by various manufacturers. Monacolin K and monacolin K acid were also measured in RYR supplements and their ratios were compared to their respective δ13C values. Previous studies suggest monacolin K and monacolin K acid have a fixed ratio in natural RYR products and large deviations may indicate the addition of lovastatin.
