Water-soluble complexes of orange pigments from Monascus sp. with HP-β-CD: Preparation, inclusion mechanism, and improved stability

Monascus pigments (Mps) have been utilized as natural food colourants in Asia for centuries. However, the poor water-solubility and photo-instability greatly restrict their applications in food industry. As a kind of orange Mps, monascorubrin (denoted as O1) is easy to react with substances containing amino groups (named amination reactions) and turn to red colour consequently. In this study, to maintain the original colour, solid inclusion complexes of O1 with hydroxypropyl-β-cyclodextrin (HP-β-CD) were prepared using freeze-drying method, and then investigated by SEM, FT-IR, PXRD, 1HNMR as well as molecular simulation method. Obtained results indicated that water solubility of O1 is significantly improved and its orange colour is successfully maintained at pH 3.5–9.0 upon complexation with HP-β-CD. Structural analysis suggested that O1 is encapsulated into the cavity of HP-β-CD, probably preventing it from amination reactions. Moreover, the pH and photo stability of Mps are markedly enhanced by complexation. This study provides an effective method for preparing water-soluble orange Mps that might be applicable in the beverage industry.