Compendium of the most significant studies with reference to properties, intake, effects.

Chiru, T. A. T. I. A. N. A. (2009). Phytochemical study of Centaurea cyanus L. USAMV Bucharest, Series A, 52, 293-297.

Abstarct  In this work it was proposed to undertake the study of phenolic compounds present not only in the species of Centaurea cyanus L. with blue flowers (which are used in medicine), but also with the flowers of other colors (red, pink), which are not valued until now. By qualitative determination, using chemical reaction and chromatography, some groups of phenolic compounds were established: phenilpropanic substances, flavonoids, anthocyanins and tannins. The total of phenilpropanic compounds, flavonoids and anthocyanins was determined spectrophotometrically, the total of tannins – using titration. These analysis have clarified the differences between the concentration of active principles in the blue flowers and those of another color. It was determined that anthocyanins, the main metabolites that confer a C. cyanus L. its pharmacological effects - diuretics, antiinflamateur, healing and so on, are more concentrated in red inflorescences (4-5 times more anthocyanins then in blue inflorescences). Other phenolic compounds also have a higher amount in the red flowers then in the blue. 

Fernandes, L., Casal, S., Pereira, J. A., Saraiva, J. A., & Ramalhosa, E. (2018). Effects of different drying methods on the bioactive compounds and antioxidant properties of edible Centaurea (Centaurea cyanus) petals. Brazilian Journal of Food Technology, 21.

Abstract. The present study aimed to evaluate the effects of hot-air convective drying, shade drying and freeze-drying on the bioactive compounds and antioxidant activity of Centaurea ( Centaurea cyanus L.) petals, as well as on several of their physicochemical properties. All the dried samples showed different appearances as compared to fresh petals, with lower titratable acidity, lower carotenoids and hydrolysable tannins contents, and greater antioxidant activity. Of the drying methods, shade drying presented the highest values for monomeric anthocyanins, flavonoids, hydrolysable tannins, total reducing capacity and antioxidant activity. By contrast, greater losses were observed as a result of hot-air convective drying. Thus shade drying is a highly promising process that should be considered as a suitable drying method for Centaurea petals.

Escher, G. B., Santos, J. S., Rosso, N. D., Marques, M. B., Azevedo, L., do Carmo, M. A. V., ... & Granato, D. (2018). Chemical study, antioxidant, anti-hypertensive, and cytotoxic/cytoprotective activities of Centaurea cyanus L. petals aqueous extract. Food and chemical toxicology, 118, 439-453.

Abstract. This study aimed to optimise the experimental conditions of extraction of the phytochemical compounds and functional properties of Centaurea cyanus petals. The following parameters were determined: the chemical composition (LC-ESI-MS/MS), the effects of pH on the stability and antioxidant activity of anthocyanins, the inhibition of lipid peroxidation, antioxidant activity, anti-hemolytic activity, antimicrobial, anti-hypertensive, and cytotoxic/cytoprotective effect, and the measurements of intracellular reactive oxygen species. Results showed that the temperature and time influenced (p ≤ 0.05) the content of flavonoids, anthocyanins, and FRAP. Only the temperature influenced the total phenolic content, non-anthocyanin flavonoids, and antioxidant activity (DPPHradical dot). The statistical approach made it possible to obtain the optimised experimental extraction conditions to increase the level of bioactive compounds. Chlorogenic, caffeic, ferulic, and p-coumaric acids, isoquercitrin, and coumarin were identified as the major compounds in the optimised extract. The optimised extract presented anti-hemolytic and anti-hypertensive activity in vitro, in addition to showing stability and reversibility of anthocyanins and antioxidant activity with pH variation. The C. cyanus petals aqueous extract exhibited high IC50 and GI50 (>900 μg/mL) values for all cell lines, meaning low cytotoxicity. Based on the stress oxidative assay, the extract exhibited pro-oxidant action (10–100 μg/mL) but did not cause damage or cell death.

Lockowandt, L., Pinela, J., Roriz, C. L., Pereira, C., Abreu, R. M., Calhelha, R. C., ... & Ferreira, I. C. (2019). Chemical features and bioactivities of cornflower (Centaurea cyanus L.) capitula: The blue flowers and the unexplored non-edible part. Industrial Crops and Products, 128, 496-503.

Abstract.  Cornflower is a flowering weed and ornamental plant whose blue flowers have been used for food, decorative and colouring purposes. In this study, the upper (edible flowers) and lower (non-edible receptacle and involucre) parts of the capitulum were studied and compared for their chemical composition and bioactive properties. The flowers were richer in tocopherols, organic acids, and apigenin derivatives (mainly apigenin-7-O-glucuronide-4′-O-(6-O-malonylglucoside)) than the non-edible bristly part (where syringic acid predominated). Four cyanidin derivatives were identified in the flowers. The extract of the non-edible part was more efficient in inhibiting the formation of thiobarbituric acid reactive substances (TBARS), the bleaching of β-carotene, and the haemolysis of the erythrocytes membrane. In general, the extracts were more active against Gram-positive bacteria and had no cytotoxicity against non-tumour liver PLP2 cells. Therefore, while flowers are a potential source of natural cyanidin-based colorants, the lower part of the capitulum has bioactive properties to be exploited in different food or pharmaceutical formulations.

Fernandes, L., Pereira, J. A., Saraiva, J. A., Ramalhosa, E., & Casal, S. (2019). Phytochemical characterization of Borago officinalis L. and Centaurea cyanus L. during flower development. Food Research International, 123, 771-778.

Abstract The present work details the nutritional and chemical compositions of borage and centaurea, at three flowering stages. Water was the main constituent, followed by total dietary fiber. Both flowers showed statistically different (p < 0.05) nutritional and chemical profiles, although in both, polyunsaturated fatty acids (PUFAs) (mainly linoleic and α-linolenic acids), free sugars (3.9–28.9% dw as fructose, glucose, and sucrose), tocopherols (with the major contribution of α-tocopherol from 1.24 to 2.75 mg/100 g dw), carotenoids (0.2–181.4 mg/100 g dw, mainly as lutein), and organic acids (6.1–14.4 g/100 g dw, mainly malic, succinic, and citric acids) were quantified. Concerning flowering, significant differences (p < 0.05) were found for some components, particularly carotenoids; however, no specific trend was observed in either of the two flower species. Thus, the present study shows that each flower species, as well as their flowering stages, may have different phytochemical and nutritional compositions. Copyright © 2019 Elsevier Ltd. 

Escher GB, Santos JS, Rosso ND, Marques MB, Azevedo L, do Carmo MAV, Daguer H, Molognoni L, Prado-Silva LD, Sant'Ana AS, da Silva MC, Granato D. Chemical study, antioxidant, anti-hypertensive, and cytotoxic/cytoprotective activities of Centaurea cyanus L. petals aqueous extract. Food Chem Toxicol. 2018 Aug;118:439-453. doi: 10.1016/j.fct.2018.05.046.  

Abstract. This study aimed to optimise the experimental conditions of extraction of the phytochemical compounds and functional properties of Centaurea cyanus petals. The following parameters were determined: the chemical composition (LC-ESI-MS/MS), the effects of pH on the stability and antioxidant activity of anthocyanins, the inhibition of lipid peroxidation, antioxidant activity, anti-hemolytic activity, antimicrobial, anti-hypertensive, and cytotoxic/cytoprotective effect, and the measurements of intracellular reactive oxygen species. Copyright © 2018 Elsevier Ltd.  

Litvinenko, V. I., & Bubenchikova, V. N. (1988). Phytochemical study of Centaurea cyanus. Chemistry of Natural Compounds, 24(6), 672-674.

Abstract. Flavonoid aglycons (quercetin, kaempferol, isorhamnetin, apigenin, luteolin, hispidulin) and their glycosides, and caffeic, chlorogenic, neochlorogenic, and isochlorogenic acids have been isolated from the epigeal part of theCentaurea cyanus L. and have been identified, and ten amino acids have also been identified.