Exploring the Optical Properties of Carotenoid-Based Nanoparticles: The Role of Terminal Groups

Carotenoids are increasingly used as naturally occurring food colorants. For application as beverage colorants, fat-soluble carotenoids are formulated into dispersion systems via nanoparticle (NP) formation. In recent years, the antioxidant properties of carotenoids have gained immense recognition for their preventive health benefits, thereby highlighting further interest in their development as functional food ingredients. Although functional carotenoids in dispersion-based formulations are desirable, knowledge regarding the structural and optical properties of NPs of carotenoids other than those of β-carotene, and methods to efficiently produce and compare NPs of various carotenoids, remain scarce. In this study, NPs of β-carotene, lycopene, astaxanthin, and lutein were prepared using a simple reprecipitation method, with a focus on understanding the variations in the molecular self-assembly influenced by the quality of solvent used during reprecipitation. This study presents the novel finding that the terminal groups of carotenoids significantly affect the intermolecular interactions, thereby altering the structural and optical properties of the resulting NPs. Our findings are expected to contribute to the development of new technologies for controlling the color of carotenoids based on the crystal structure of the NPs.