AimsRed yeast rice (RYR), produced by inoculating Monascus strains to steamed rice, contains many kinds of physiologically bioactive compounds, among which monacolin K can be used as an antihypercholesterolaemic agent. However, RYR can be polluted by the mycotoxin citrinin, which has nephrotoxic and hepatotoxic activities. To avoid the risk of citrinin contamination in Monascus fermented products, it is important to screen for Monascus strains that produce no or low citrinin.Methods and ResultsFive autochthonous Monascus strains with high‐yield monacolin K and undetectable citrinin were obtained using high‐performance liquid chromatography (HPLC). All five strains were identified as Monascus ruber based on Genealogical Concordance Phylogenetic Species Recognition criteria. Polymerase chain reaction revealed that citrinin polyketide synthase (pksCT) gene was found in these strains, but transcriptional regulator (ctnA) was not found.ConclusionsFive strains are potential strains for producing high‐quality RYR. The distribution of the pksCT gene was not restricted to Monascus purpureus and Monascus sanguineus, and M. ruber strains were diverse in pksCT and ctnA genes.Significance and Impact of the StudyThe integration of citrinin HPLC analysis and pksCT and ctnA genes amplification could provide a complementary approach in valuable Monascus strains screening.
Ca 0.66 Ti 0.66 Nd 0.34 Al 0.34 O 3 (CTNA) ceramics were prepared by solid-state reaction method and their sintering behavior, microwave dielectric properties , and microstructure were investigated. CTNA ceramics were examined by Raman scattering to reveal the correlation of perovskite structure with the microwave properties. It found that the area of peak A 1g (O) stretch mode reflects the quality factor Q × f value in the perovskite materials. This concludes that the oxygen octahedron plays an important role of the material's microwave performance. Sintering temperature affected the unit cell volume and the lattice parameters of the CTNA ceramics, the grain size distribution, the Gibbs free energy, the thermal expansion coefficient (CTE), and the dielectric properties ( ε r , Q × f , τ f ). The samples sintered at 1500 °C displayed the best dielectric constant and Q × f , as 44.94 and 41922.22 GHz, respectively.
Similar to Pu-erh tea, Liupao tea is a post-fermented tea that is produced through natural fermentation by microorganisms. Penicillium citrinum is involved in multiple production processes of Liupao tea that can produce citrinin, a secondary metabolite with renal toxicity; however, the effect of P. citrinum on the quality of Liupao tea has not been investigated yet. Citrinin production is regulated by approximately 16 biosynthesis genes. However, little is known about the genetic background of citrinin in the complex Liupao tea system. In the present study, we cultured P. citrinum on potato dextrose agar and Liupao tea powder media and analyzed the changes of its nutritional components in Liupao tea. We selected six citrinin biosynthesis genes identified in Monascus exhibiting homology and high sequence similarity to those in P. citrinum and further analyzed the expression of citrinin biosynthesis genes in Liupao tea and the changes in citrinin yield. The results showed that the changes in nutritional components of Liupao tea were closely related to the growth and metabolism of P. citrinum and the quality of the tea. Decreases in the contents of soluble sugars (from 10.29% to 9.58%), soluble pectins (from 3.71% to 3.13%), free amino acids (from 3.84% to 3.14%), and tea polyphenols (from 22.84% to 18.78%) were noted. The Spearman’s correlation analysis indicated that P. citrinum growth can improve the tea quality to some extent. Quantitative real-time PCR demonstrated that ctnA gene was a positive regulator of citrinin production regardless of the culture medium used. ctnA and orf5 expressions greatly influenced the metabolism of citrinin by P. citrinum in Liupao tea. In conclusion, the citrinin biosynthesis genes, ctnA and orf5 , may be the promising targets for developing strategies to control P. citrinum infection and citrinin biosynthesis in Liupao tea.
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