Astaxanthin is a lipophilic carotenoid pigment well-known for its potent antioxidant activity. The astaxanthin currently available on the market is mainly found as esterified astaxanthin, naturally produced by Haematococcus, a eukaryotic microalga capable of synthesizing this compound. Due to its vivid orange color and powerful antioxidative properties, astaxanthin is widely utilized in the cosmetics, pharmaceuticals, and functional food industries for diverse health-promoting effects.
Our laboratory isolated Coelastrella astaxanthina Ki-4 (Scenedesmaceae), a novel species of green microalga from an asphalt surface in midsummer, Japan. The Ki-4 strain was found to produce a unique water-soluble orange carotenoprotein that predominantly binds astaxanthin, named AstaP. AstaP is the first protein discovered in photosynthetic organisms and is produced in large amount under environmental stress conditions accompanied by intense light exposure.
We are currently investigating the application of AstaP in cosmetics and food products, taking advantage of its water-solubility and highlighting its potential for the mass production of natural microalgal pigments derived from photosynthetic reactions. Reflecting the properties of the microalga that can survive under extreme environmental conditions, AstaP demonstrated remarkable heat stability. Considering its potential for industrial use, we evaluated the physicochemical stability of AstaP across a wide range of temperature, pH, light intensity, and repeat freeze-thaw cycles, in comparison with natural phycocyanin using commercially available Lina Blue® derived from the cyanobacteria Spirulina. In this study, AstaP shows highly stable biofunctional properties, providing new insights into carotenoid solubilization mechanisms in photosynthetic organisms with promising potential as a sustainable biomaterial for industrial and health-related applications.