Monascus spp. have been used for the production of natural pigments and bioactive compounds in China for several centuries. Monascus can also produce the mycotoxin citrinin, restricting its use. Disruption of the pksCT gene in Monascus aurantiacus Li AS3.4384 reduces citrinin production capacity of this strain (Monascus PHDS26) by over 98%. However, it is unclear how other metabolites of M. aurantiacus Li AS3.4384 (the wild-type strain) are affected by the pksCT gene. Here, we used metabolomic analyses to compare red yeast rice (RYR) metabolite profiles of the wild-type strain and Monascus PHDS26 at different stages of solid-state fermentation. A total of 18 metabolites forming components within the glycolysis, acetyl-CoA, amino acid, and tricarboxylic acid (TCA) cycle metabolic processes were found to be altered between the wild-type strain and Monascus PHDS26 at different stages of solid-state fermentation. Thus, these findings provide important insights into the metabolic pathways affected by the pksCT gene in M. aurantiacus.

A simple and reliable HPLC–UV method was developed for the simultaneous determination of two orange pigments, rubropunctatin (RPT) and monascorubrin (MSB), in red yeast rice. Alcohols were found unsuitable for the extraction of these pigments because they chemically reacted with the pigments to afford new compounds. Thus, acetonitrile/H2O was used as the mobile phase for the chromatographic separation of RPT and MSB. Under optimal conditions, good linearity was obtained over the concentration range of 0.25–50.0 μg mL−1 and 0.5–50 μg mL−1 for RPT and MSB, respectively, with a correlation coefficient (R2) of >0.9994. The limits of detection and quantification were 0.05 and 0.15 μg mL−1, respectively, for RPT, and 0.10 and 0.30 μg mL−1, respectively, for MSB. The recoveries of RPT and MSB in red yeast rice were 91.9–101 % and 89.8–102 %, respectively, with relative standard deviations of <5.0 %. This assay was successfully used to measure the amount of RPT and MSB produced by Monascus spp. at different fermentation times.