astaxanthin keto-carotenoid, structural chemical formula

astaxanthin structural formula krill shrimp molecule chemistry supplement structure chemical pigment compound salmon lobster keto crustacean antioxidant molecular ketocarotenoid xanthophyll haematococcus carotenoid terpene oxygen carbon line carotene group organic skeletal hydrogen education food blue pink study bond biochemistry medicine substance chain model research symbol keto-carotenoid background