Oxidation evaluation of free astaxanthin and astaxanthin esters in Pacific white shrimp during iced storage and frozen storage

Abstract 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