Quality and Authenticity Evaluation of Red Yeast Rice Food Supplements from the Bulgarian Market

Red yeast rice (RYR) food supplements show substantial variability in monacolin composition, raising concerns regarding product quality, labelling accuracy, and regulatory compliance. This study evaluated 14 RYR-containing food supplements purchased from the Bulgarian market using complementary HPLC-PDA, LC-MS, and GC-MS/MS approaches. A validated HPLC-PDA method was applied for quantitative determination of the lactone form of monacolin K (MK) and monascorubrin, while LC-MS was used for identity confirmation and GC-MS/MS for targeted screening of undeclared simvastatin and rosuvastatin. The measured lactone MK intake at the maximum manufacturer-recommended daily dose ranged from 0.06 to 14.11 mg/day, demonstrating substantial product-to-product variability and discrepancies between measured MK concentrations and label declarations. Three products contained lactone MK at levels of ≥3 mg/day. However, because the hydroxy acid form and other monacolins were not quantified, these results cannot be directly interpreted as total RYR-derived monacolin intake for regulatory assessment. Neither simvastatin nor rosuvastatin was detected under the applied analytical conditions. Monascorubrin was not detected in any of the analysed products under the applied analytical conditions; consequently, its non-detection cannot substantiate product authenticity, and the present findings do not support its use as a standalone authenticity marker for finished RYR supplements. Overall, the results demonstrate substantial variability in measured MK-lactone content among RYR food supplements purchased from the Bulgarian market and highlight the importance of improved analytical characterisation and product standardisation.