Astaxanthin content, structure and antioxidant activity in the processing of Antarctic krill (Euphausia superba) meal

Euphausia superba is rich in astaxanthin, which is a good source of natural astaxanthin. Shrimp meal is one of the most important processed products of E. superba. In the shrimp meal processing, the cooking and drying processes involve heat treatment. Astaxanthin is a heat-sensitive substance with poor structural stability, and it is easy to be degraded and isomerized at high temperature, which results in the changes of astaxanthin content and antioxidant capacity. In order to understand the changes of astaxanthin content, structure and antioxidation ability during the processing of E. superba meal, the content and structure of astaxanthin in each stage were determined by high-performance liquid chromatography, the antioxidant activity of astaxanthin in different processing stages was compared, and the correlation between astaxanthin structure and its functional activity was analyzed. The results showed that the content of astaxanthin in E. superba was 110.6 mg/kg, of which the content of all-trans astaxanthin was 90.7% , the content of 13-cis astaxanthin and 9-cis astaxanthin were 4.7% and 4.6% respectively, and after cooking and drying, the content of astaxanthin was 88.7 and 52.1 mg/kg, the proportion of trans astaxanthin was 76.2% and 72.2% , the proportion of 13-cis astaxanthin was 19.9% and 21.9%, and the proportion of 9-cis astaxanthin was 3.9% and 5.9%. The content of three optical isomers such as 3S, 3’S, 3S, 3’R, 3R, 3’R in astaxanthin of E. superba were 16.8, 17.9 and 72.1 mg/kg respectively, the content were 12.0, 25.5 and 55.3 mg/kg after cooking, and were 2.8, 8.1 and 12.4 mg/kg after drying. The scavenging capacity of astaxanthin to DPPH free radical was stronger than Vc. In the scavenging experiment of hydroxyl free radical, the antioxidation ability of astaxanthin after cooking and drying was better than krill material. In FRAP iron reduction experiment, the antioxidation after cooking and drying also showed greater reduction ability. The results showed that the geometric isomerization of astaxanthin mainly took place in the cooking stage, and the optical isomerization mainly took place in the drying stage. This study can provide a theoretical basis and technical reference for the optimization of the processing technology of E. superba meal and the extraction and utilization of astaxanthin.