Stable isotope ratio analysis for authentication of red yeast rice

Red yeast rice (RYR) is a dietary supplement obtained from rice fermented with the mould Monascus purpureus. It contains Monacolin K which is a hypocholesterolemic statin used to prevent cardiovascular diseases. The homologous prescription biosynthetic statin, lovastatin, is not chemically distinguishable from monacolin K. In this work we investigated whether δ13C and δ2H can distinguish monacolin K from lovastatin and can detect the presence of lovastatin in RYR. 18 samples of red yeast rice powder and 18 samples of lovastatin were collected. Monacolin K was isolated from RYR using preparative HPLC and together with lovastatin, was subjected to analysis of δ13C and δ2H using Isotope Ratio Mass Spectrometry. Thanks to the different photosynthetic cycles of the matrices used for their synthesis, monacolin K and lovastatin have different δ13C values (−29.6‰ ± 0.6 and −16.7‰ ± 2.6 respectively). δ2H is significantly (p < 0.001) lower in monacolin K but the ranges of values partially overlap with those of lovastatin. By defining a δ13C threshold value of −28.3‰ for monacolin K, addition of lovastatin from a minimum of 10% can be identified. δ13C analysis can be therefore proposed as a suitable tool for detecting the authenticity of RYR on the market.