Background: In this paper, the changes in free astaxanthin (F-AST) and astaxanthin esters (AST-Es) in Litopenaeus vannamei during iced storage and frozen storage were investigated. The liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry method was used to quantify the molecular species of AST-Es in shrimp during storage.
Results: Based on the analysis of autoxidation products, apo-12-astaxanthinal and apo-13-astaxanthinone docosahexaenoic acid (DHA) ester were identified as the major oxidation products of F-AST and AST-Es in L. vannamei during storage. The total astaxanthin (T-AST) content decreased by 34.51% after 7 days in iced storage. In contrast, the content of T-AST decreased by 43.76% after 12 weeks in frozen storage. The content of F-AST decreased by 29.99% while 13-cis-astaxanthin increased after 3 days in iced storage, which indicated that degradation of AST was accompanied by isomerization. Total volatile basic nitrogen and T-AST content showed a significant negative correlation while in frozen storage, where the concentration of T-AST might be one indicator to evaluate shrimp freshness.
Conclusion: The correlation coefficients between phenol oxidase, lipoxygenase, apo-12-astaxanthinal, and apo-13-astaxanthinone DHA ester were all greater than 0.97 (P < 0.01). This correlation indicates that phenol oxidase and lipoxygenase were the main internal factors to improve oxygenation of astaxanthin in L. vannamei. These results provide a theoretical basis for further study of oxidation and the degradation mechanism in astaxanthin, as well as a new idea for the development and utilization of astaxanthin compounds in Pacific white shrimp. © 2018 Society of Chemical Industry.
Keywords: LC-APCI-MS/MS; Litopenaeus vannamei; astaxanthin; oxidation mechanism; storage.
© 2018 Society of Chemical Industry.