Extraction And Puirifcation Of Astaxanthin From Antarctic Krill Shells

Astaxanthin is a kind of carotenoid with potent antioxidant activity and tinting strength widelyused in food, medicine, cosmetics and feed industries. Shrimp shell is an important resource ofnatural astaxanthin. Astaxanthin was extracted and purified from Antarctic krill shells to achieve thecomprehensive utilization ofAntarctic krill.Firstly, pretreatment methods were explored. The effects of crushing, drying, acidolysis andenzymatic treatment on extraction rate of carotenoids were studied. The results showed that, dryingand acid pretreatments of the shells lead to a great loss of pigments, while the proper crushingcontributed to the extraction by solvents.After enzymatic treatment by Alcalase, krill residue,pigment precipitation and protein solution were obtained, and the content of total carotenoids in theresidue and pigment precipitation were60.3μg/g and268.5μg/g shell (dry basis) respectively.Secondly，the extraction condition of carotenoids was analysed. The effects of different organicsolvents, solid-liquid ratio, extraction temperature, extraction time on extraction rate of carotenoidswere studied with shell’s residue and pigment precipitation as materials respectively. The resultsshowed that, acetone was the optimal extraction solvent for residue and the optimal extractioncondition was solid-liquid ratio1:5, extraction time3.5h, extraction temperature40℃with15.6%of extraction rate obtained. Ethanol was the optimal extraction solvent for precipitation andthe optimal extraction condition was solid-liquid ratio1:4, extraction time2.0h, extractiontemperature40℃with73.7%of extraction rate obtained.Then the saponification condition was explored. The effect of pigment concentration,saponification temperature and alkali concentration were studied and suitable saponificationconditions were obtained, namely crude extract concentration0.1g/mL, saponification temperature5℃, alkali concentration0.020mol/L and55.75μg/mL of free astaxanthin was obtained at12h ofsaponification.Also，the separation and purification conditions of astaxanthin were studied. The adsorptioneffect of AB-8and desorption conditions of astaxanthin were studied. The result showed that, themaximum adsorption content of astaxanthin was476.2μg/g dry AB-8. Ethyl acetate was selected asthe eluting solvent with desorption rate98.7%. The dynamic adsorption conditions were obtained,namely astaxanthin concentration2μg/mL, rate4BV/h. Under this condition, astaxanthin insaponification solution was purified with recovery rate of78.9%and purity of92.4%. Then silicagel column was used for further purification with recovery rate of92.9%and purity of97.1%.Lastly，the stability of astaxanthin was analysed. The retention rate and DPPH scavenging wasstudied in different conditions, such as the light, temperature, pH and metal ions. The resultsshowed that astaxanthin was quite unstable under light, high temperature and acid conditions, whileFe2+、Cu2+and Fe3+can also cause the loss of astaxanthin and the decline of DPPH scavenging ratio.