This study aimed to select proper lipids for designing astaxanthin-loaded nanostructured lipid carriers (astaxanthin-NLC), and then to evaluate the influence of formulation composition on astaxanthin-NLC characteristics and optimize the formulation by response surface methodology. Tween 80 and lecithin were employed as emulsifier, and oleic acid and glyceryl behenate were selected as appropriate lipids. Astaxanthin-NLC (with 5% lipid phase) were prepared by melt emulsification–sonication technique and stored at ≈ 19 °C for 25 days. The lipid phase to Tween 80 ratio (LTR) and oleic acid content of the lipid mixture (OCL), as independent variables, had significant effects on physical characteristics of fresh formulations and their storage stability. The optimum formulation of astaxanthin-NLC (with OCL: 22.4% and LTR: 1.8) had greater values of particle size, polydispersity index and ζ-potential than the astaxanthin-free formulation. X-ray diffraction and thermal analyses exhibited a new crystalline lattice with lower crystallinity for the optimum formulation compared to glyceryl behenate. Industrial relevance Evidence that carotenoids have many valuable physiological functions in human body persuades the manufacturers to insert them into foods and beverages. However, fortification of aqueous-based foods with carotenoids is currently limited due to their poor water-solubility, low bioavailability, and chemical instability. NLC are O/W nanoemulsions in which a major portion of the lipid phase is constituted by solid lipid, yield high encapsulation efficiency by effective-immobilization of the encapsulated lipophilic compounds, and can therefore improve their utilization, bioavailability and stability in fat-free and low-fat foods and transparent/opaque beverages. In order to design an appropriate formulation of astaxanthin-NLC, we selected a suitable lipid mixture, and investigated the effect of contents of oil and surfactant on characteristics of astaxanthin-NLC. These
