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.

BACKGROUND Compared with free astaxanthin (Asta), docosahexaenoic acid astaxanthin monoester (Asta‐C22:6) has higher stability and bioavailability. However, Asta‐E is still unable to be used in the water system. Hence it is necessary to build a water‐soluble delivery system. In this study, Asta‐C22:6 microemulsion and microcapsule using whey protein isolate (WPI) and hydroxypropyl‐β‐cyclodextrin (HPβ‐CD) as composite wall material were prepared. They were added to three dairy products (milk powder, yogurt and flavored dairy product). A dairy product rich in Asta‐C22:6 with high bioavailability was designed by measuring quality characteristics, sensory evaluation and in vivo experiments. RESULTS Compared with spray drying, the freeze‐drying microcapsule had a higher encapsulation efficiency (72.5%), water content (4%) and better solubility, and Asta‐C22:6 microcapsule (1 g L−1) yogurt had the best quality. The bioavailability of Asta‐C22:6 microcapsule yogurt was further evaluated. After a single oral dose in mice, the bioavailability of Asta‐C22:6 microcapsule in yogurt was significantly increased (Cmax = 0.31 μg mL−1, AUC0–T = 3.20 h μg mL−1). CONCLUSION We successfully prepared Asta‐C22:6 microcapsule yogurt, which improved the stability and bioavailability of Asta. The present research is meaningful for delivering unstable bioactive small molecules based on WPI and HPβ‐CD. It provides an experimental basis for the application of Asta‐C22:6 and the development of functional dairy products. © 2022 Society of Chemical Industry.