Research progress on extraction, biological activities and delivery systems of natural astaxanthin

Astaxanthin (AST) is a kind of carotenoid natural pigment that has been widely found in plants, crustaceans' shell, flamingos' feathers and microorganisms. Due to its various biological activities, AST has suggested as an important compound in biochemical researches and has great application potentials in cosmetics, human nutritional health products, as well as medicines. Unfortunately, the poor water solubility, chemical instability and low oral bioavailability make AST difficult to be applied in food systems. Besides, the amount of natural AST is limited, and how to extract and utilize AST efficiently is in great demand. This review highlights the considerable potential of AST products in food processing by evaluating the advantages and disadvantages of different extraction strategies. Moreover, AST have some shortages on physicochemical properties, which limits its application in foods. Therefore, the review focuses on the comparison and discussion of different AST-loaded delivery systems, as well as its application status. Natural AST are commonly extracted from Haematococcus pluvialis, crustaceans, and bird feathers by corresponding appropriate methods. Solvent extraction, oil stripping, enzymatic hydrolysis, supercritical fluid extraction and microwave-assisted extraction are mostly applied to accumulate AST with high yields. Delivery systems such as emulsions, nanoparticles and liposomes may improve the stability and bioavailability of AST.