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.