In this study, the effects of different pretreatments (enzymatic treatment, freezing and soaking in ice-salt solution mixture) on the peeling of the Pacific white shrimp Penaeus vannamei and myofibrillar proteins in it were investigated. Shrimp peelability, the texture of peeled shrimps and the physicochemical and structural characteristics of myofibrillar proteins were analyzed after pretreatment. The results showed that compared with the two other pretreatments, enzymatic pretreatment for 3.5 h reduced the work required to peel shrimps and resulted in no significant difference in complete peeling rate (P > 0.05). The enzymatic treatment markedly decreased Ca²⁺-ATPase activity, the contents of total sulfhydryl and active sulfhydryl and intrinsic fluorescence intensity. The contents of total sulfhydryl and active sulfhydryl and intrinsic fluorescence intensity but not Ca²⁺-ATPase activity were decreased less by the enzymatic treatment than by freezing and ice-salt solution treatment. Enzymatically treated shrimps had no significant difference in surface hydrophobicity and protein carbonyl content compared with fresh and ice salt-treated samples, respectively (P > 0.05). Fourier transform infrared (FTIR)spectroscopic analysis showed that the contents of α-helix and β-turn in myofibrillar proteins were not significantly changed after pretreatment (P > 0.05), but the enzymatic and ice-salt treatments resulted in the transformation of β-sheet to random coil. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that freezing and ice-salt treatment changed the conformation but not the SDS-PAGE pattern of myofibrillar proteins. The enzymatic treatment caused the degradation of some macromolecular proteins, but did not cause a significant difference in the texture characteristics of shrimp meat compared with freezing and ice-salt treatment.

In order to improve the drying rate and rehydration of tilapia meat, the freeze-drying characteristics and quality changes of blanched or steamed fish meat were analyzed. The effect of heat pretreatment on the quality of freeze-dried fish meat was elucidated by considering the denaturation degree of myofibrillar protein, water distribution and microstructural changes in fish meat during the drying process. The results showed that heat pretreatment could effectively improve the drying rate of tilapia meat, shortening the drying time by nine hours compared with the control group; blanching was more effective than steaming. The rehydration temperature range for tilapia meat was expanded by heat pretreatment, and good rehydration was observed at 50–80 ℃. The rehydration temperature for the control samples was 80 ℃, and the rehydration rate of the 10 min heat treatment group was more than 60%, indicating that the dried product can be rapidly rehydrated. The hardness of the rehydrated fish meat was similar to that of cooked fresh fish meat, and it had good mouthfeel. Heat pretreatment caused significant denaturation of myofibrillar protein and consequently changes in water distribution and a conspicuous increase in the peak area of transverse relaxation time T₂₃, indicating that the increase in free water content after heat treatment is an important reason for the increase in freeze-drying rate. The experimental results can provide technical support for the development of ready-to-eat dried fish products that are suitable for rehydration.

This study investigated the effects of different carriers on the digestion and absorption of astaxanthin from Pacific white shrimps aiming to provide a reference for the development and utilization of astaxanthin. Astaxanthin liposomes and astaxanthin microcapsules were successfully prepared by the thin-film ultrasonic method and the antisolvent precipitation method, respectively, and their physiological and biochemical properties were evaluated. Experimental results showed that excess amounts of wall material made the system unstable, thereby impacting the encapsulation efficiency. Additionally, a larger amount of the stabilizer cholesterol in liposomes did not necessarily lead to better results. Under optimized conditions, the encapsulation efficiencies of both astaxanthin liposomes and microcapsules were above 85%, the former being somewhat higher than the latter. The optimized preparation conditions for astaxanthin microcapsules were 2.5% zein concentration, 0.005% astaxanthin stock solution, and ultrapure water at pH 7, and those for astaxanthin were 4% soy lecithin concentration, 0.6% cholesterol concentration, and 0.004% astaxanthin stock solution concentration. Particle size analysis and transmission electron microscopy (TEM) showed that both samples were spherical particles of approximately 100 nm in diameter with smooth surfaces and fully encapsulated structures. In storage stability experiments, freeze-dried microcapsule powder exhibited the highest retention rate of astaxanthin (82.57%), but when preserved in liquid form, the retention rate of astaxanthin microcapsules was lower than that of astaxanthin liposomes. Encapsulated astaxanthin had higher antioxidant capacity than astaxanthin-containing oil at the same concentration. In in vitro simulated gastrointestinal digestion, the digestibilities of both astaxanthin liposomes and microcapsules were above 86%, the former being the latter. Both of them were immune to simulated gastric juice, and astaxanthin was slowly released from them in the simulated intestinal environment after gastric digestion, ensuring its absorption and utilization in the intestine tract. Astaxanthin-containing oil, astaxanthin liposomes and microcapsules diluted 5 and 10 folds were non-toxic to Caco-2 cells, and inhibited the production of reactive oxygen species (ROS) in oxidatively stressed cells. Among them, astaxanthin liposomes exhibited the highest absorption and transport efficiency and the strongest antioxidant activity. Astaxanthin, oil, lecithin, and zein could be absorbed by Caco-2 cells, but due to the limitations of conditions, Caco-2 cells absorbed more astaxanthin liposomes and astaxanthin-containing oil.

The objective of this study is to identify the antioxidant peptides from shrimp by-products and clarify the underlying protective mechanism involved in HepG2 cells with oxidative stress induced by H₂O₂. Protein from shrimp by-products was hydrolyzed by three enzymes (neutral protase, alcalase, and Protamex) and the hydrolysates were separated by using Sephadex G-15 gel filtration, among which the A3 (fraction of alcalase-hydrolysate) displayed a significant 1,1-diphenyl-2-picrylhydrazyl radical and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) cation radical scavenging ability. A total of 3 480 peptides were identified through nano-high performance liquid chromatography-tandem mass spectrometry, with the prediction of five discovered antioxidant peptides (DYPLVPPYF, HFVPVYEGF, GFPPFTGGPFR, EGYPFNPLL, and RVSDGPWLGR). Notably, HFVPVYEGF and EGYPFNPLL emerged as the potent antioxidant peptide, displaying lower half maximal inhibitory concentration. Furthermore, HFVPVYEGF and EGYPFNPLL obviously relieved oxidative stress in HepG2 cells, which strengthened the activity of total-antioxidant capocity, catalase, glutathione peroxidase, and superoxide dismutase, with diminishing the intensity of malondialdehyde and intracellular reactive oxygen species. Molecular docking results revel that HFVPVYEGF and EGYPFNPLL can bind to Kelch-like ECH-associated protein 1 with hydrophobic interactions. The results provided theoretical basis for the production and application of the by-product of shrimp. And a further study should be carried out to examine the bioavailability and in vivo activity of HFVPVYEGF and EGYPFNPLL which identified from shrimp by-products.