Preparation And Properties Of Astaxanthin-loaded Calcium Alginate Microparticles

The powerful antioxidant and biological activities of astaxanthin are conferred by its unique molecular structure, which consists of hydroxyl (—OH) and keto (C=O) moieties on each ionone ring. However, applications of astaxanthin are restricted due to its unstable structure—the 11 conjugated carbon-carbon double bonds, which are particularly susceptible to oxidation in harsh enviroments like high temperature, acidic environment, the presence of light and oxygen etc. Consequently, this structural transformation causes the loss of biological activity. In addition, astaxanthin, similar to other lipophilic carotenoids, has low bioavailability, resulting in limited in vivo antioxidant activity. It has been reported that encapsulation technology could improve the stability of astaxanthin, however the microparticles prepared by the conventional methods always with low encapsulation efficiency and wide size distribution. In this research, astaxanthin-loaded calcium alginate microparticles with uniform size, good dispersibility and high encapsulation efficiency were prepared using a two-emulsions gelation method, aiming to improve the stability and water-dispersion of astaxanthin, and at the same time, its anti-tumor activity was investigated in vitro.The optimal emulsification condition was determined by investigating the stability of emulsion:4000 r/min shearing rate,5 min emulsifying time,4%(v/v) Span 80 concentration, the oil-water ratio of 1:1. The emulsion was stable and with 2.0-3.0?m uniform size prepared under the optimal emulsification. The optimal condition for preparing calcium alginate microparticles was determined by univariate analysis:10%(w/v) calcium chloride concentration,1% sodium alginate concentration and 15? reaction temperature. The size of microparticles ranged from 0.8 to 3.0?m with a mean size of 1.5?m and narrow size distribution (PDI=0.15).The amount of astaxanthin, emulsion-broking time and washing times affected the encapsulation efficiency and astaxanthin-loaded rate significantly. When the initial amount of astaxanthin was 30 mg, emulsion-broking time was 30 min and the washing time was 1, the encapsulation efficiency and astaxanthin-loaded rate were 86.1% and 15.6% respectively. The size of astaxanthin-loaded calcium alginate microparticles ranged from 0.8 to 2.0?m with a mean size of 1.6?m and narrow size distribution (PDI=0.17). Microencapsulation of astaxanthin using calcium alginate not only enhanced the stability and antioxidant activity under unfavorable conditions, also its water-dispersion.The release profiles showed only 9% astaxanthin release in pH=1.5 acidic solution and 46% in pH=7.4 alkaline solution, indicating that astaxanthin will be well protected by calcium alginate microparticles in acidic environment. The microencapsulated astaxanthin significantly inhibited the growth of Hepa cells, and showing no significant inhibition of the ADSCs.