Identification of azaphilone derivatives of Monascus colorants from Talaromyces amestolkiae and their halochromic properties

•Chemical structure and pH stability of Talaromyces amestolkiae natural colorants were studied.•Five amino-hexanedioic acid azaphilone colorants were detected.•T. amestolkiae colorants were stable in range of pH from 3 to 11.•T. amestolkiae colorants showed negative halochromism properties. Currently, the ability to produce several kinds of water-soluble red natural colorants makes the genus Talaromyces particularly important to the dye industry, which can be an alternative to the use of harmful synthetic colorants. In this study, colored compounds produced by Talaromyces amestolkiae were extracted, characterized chemically and the color stability of the fermented broth without any extraction procedure was further evaluated over pH variation. Five azaphilones compounds were detected by Ultrahigh Performance Liquid Chromatography-Mass Spectrometry system, all being complexes of the fatty acid amino-hexanedioic acid and azaphilone Monascus colorants. The color of the fermented broth was stable at a wide range of pH (3–9). Furthermore, T. amestolkiae colorants precipitated through hydrolysis of key chemical groups at extremely acidic (pH 1) and lose red color in extremely basic (pH 13) medium, showing negative halochromism. Nevertheless, these findings enhance the industrial relevance of azaphilone colorants produced by biotechnological process.