3.1. Storage stability of the astaxanthin/HPCD inclusion complex
According to our previous research (Yuan et al., 2008), mixing astaxanthin with HPCD, an orange, clear water solution was achieved. Then, the solution was freeze-dried, a pink solid state sample was obtained. Fig. 2 shows the aqueous solution and freezedried sample of astaxanthin/HPCD complex. The aqueous solubility of astaxanthin was highly enhanced (>1.0 mg/mL) after complexation. The result is similar to that of other carotenoids/cyclodextrin complexes (Pfitzner, Francz, & Biesalski, 2000). Astaxanthin should
show a good antioxidant activity under this concentration. Moreover,the
complex also has fine tinctorial power for food or cosmetic
products.
However, good antioxidant activity and tinctorial power are
depended on the storage stability of astaxanthin. Figs. 3 and 4 show
the storage stabilities of astaxanthin and the complex at 4 ◦C and
25 ◦C respectively. It can be found that the absorbance of astaxanthin
and the complex reduced slowly within test periods. The
stability of the complex was higher than that of native astaxanthin.
After 28 days test, 6.09% of native astaxanthin decomposed,
meanwhile, 4.59% of astaxanthin in the complex lost, at 4 ◦C. When
stored at 25 ◦C, 8.58% of native astaxanthin and 7.20% of astaxanthin
in the complex decomposed, respectively. The data is slightly
higher than that of 4 ◦C. Overall, both native and astaxanthin in the
Fig. 3. Storage stability of astaxanthin (a) and astaxanthin/HPCD (b) complex at 4 ◦C.
complex showed high stability under storage condition. This result
was agreed with former report (Rao, Sarada, & Ravishankar, 2007).
Complexation was helpfulto improve stability of astaxanthin under
storage condition.