title: Improved analysis of Monascus pigments based on their pH-sensitive UV-Vis absorption and reactivity properties.
abstract: Monascus pigments, a mixture of azaphilones mainly composed of red, orange and yellow pigments, are usually prepared in aqueous ethanol and analysed by ultraviolet-visible (UV-Vis) spectroscopy. The pH of aqueous ethanol used during sample preparation and analysis has never been considered a key parameter to control; however, this study shows that the UV-Vis spectra and colour characteristics of the six major pigments are strongly influenced by the pH of the solvent employed. In addition, the increase of solvent pH results in a remarkable increase of the amination reaction of orange pigments with amino compounds, and at higher pH (≥ 6.0) a significant amount of orange pigment derivatives rapidly form. The consequent impact of these pH-sensitive properties on pigment analysis is further discussed. Based on the presented results, we propose that the sample preparation and analysis of Monascus pigments should be uniformly performed at low pH (≤ 2.5) to avoid variations of UV-Vis spectra and the creation of artefacts due to the occurrence of amination reactions, and ensure an accurate analysis that truly reflects pigment characteristics in the samples.
authors.affiliation: a School of Bioscience and Bioengineering , South China University of Technology , Guangzhou 510006 , China.
authors.forename: Kan
authors.initials: K
authors.lastname: Shi
authors.affiliation: a School of Bioscience and Bioengineering , South China University of Technology , Guangzhou 510006 , China.|c Tianyi Biotech. Co., Ltd , Dongguan 523000 , China.
authors.forename: Gong
authors.initials: G
authors.lastname: Chen
authors.affiliation: a School of Bioscience and Bioengineering , South China University of Technology , Guangzhou 510006 , China.
authors.forename: Marco
authors.initials: M
authors.lastname: Pistolozzi
authors.affiliation: b Guangzhou Institute of Microbiology , Guangzhou 510663 , China.
authors.forename: Fenggeng
authors.initials: F
authors.lastname: Xia
authors.affiliation: a School of Bioscience and Bioengineering , South China University of Technology , Guangzhou 510006 , China.
authors.forename: Zhenqiang
authors.initials: Z
authors.lastname: Wu
mesh_terms: D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D032741:Monascus / Q000737:chemistry*; D010860:Pigments, Biological / Q000032:analysis*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D010860:Pigments, Biological
keywords: Monascus pigments; UV-Vis analysis; amination reaction; pH control