The sea cucumber is an essential nutrient source and a significant economic marine resource associated with successful aquaculture. However, sea cucumbers are highly susceptible to autolysis induced by endogenous protease after postmortem, and the phenomenon of body wall “melting” occurs, which seriously affects the food quality of products and the degree of acceptance by consumers. To satisfy the growing demand for fresh or processed sea cucumbers, we must clarify the autolysis mechanism of sea cucumbers and the methods to achieve autolysis regulation. In this paper, the factors leading to the quality deterioration and texture softening of sea cucumbers are reviewed, with emphasis on enzymatic characteristics, the autolysis mechanism, the effects of autolysis on the physicochemical properties of the body wall of the sea cucumber, and the development of potential natural protease inhibitors. We aim to provide some reference in future preservation and processing processes for sea cucumbers, promote new processing and preservation technologies, and advance the sea cucumber industry’s development.

Sea cucumber viscera contain various naturally occurring active substances, but they are often underutilized during sea cucumber processing. Polydeoxyribonucleotide (PDRN) is an adenosine A_2A receptor agonist that activates the A_2A receptor to produce various biological effects. Currently, most studies on the activity of PDRN have focused on its anti-inflammatory, anti-apoptotic, and tissue repair properties, yet relatively few studies have investigated its antioxidant activity. In this study, we reported for the first time that PDRN was extracted from the sperm of Apostichopus japonicus (AJS-PDRN), and we evaluated its antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS), and hydroxyl radical scavenging assays. An in vitro injury model was established using H₂O₂-induced oxidative damage in RAW264.7 cells, and we investigated the protective effect of AJS-PDRN on these cells. Additionally, we explored the potential mechanism by which AJS-PDRN protects RAW264.7 cells from damage using iTRAQ proteomics analysis. The results showed that AJS-PDRN possessed excellent antioxidant activity and could significantly scavenge DPPH, ABTS, and hydroxyl radicals. In vitro antioxidant assays demonstrated that AJS-PDRN was cytoprotective and significantly enhanced the antioxidant capacity of RAW264.7 cells. The results of GO enrichment and KEGG pathway analysis indicate that the protective effects of AJS-PDRN pretreatment on RAW264.7 cells are primarily achieved through the regulation of immune and inflammatory responses, modulation of the extracellular matrix and signal transduction pathways, promotion of membrane repair, and enhancement of cellular antioxidant capacity. The results of a protein–protein interaction (PPI) network analysis indicate that AJS-PDRN reduces cellular oxidative damage by upregulating the expression of intracellular selenoprotein family members. In summary, our findings reveal that AJS-PDRN mitigates H₂O₂-induced oxidative damage through multiple pathways, underscoring its significant potential in the prevention and treatment of diseases caused by oxidative stress.

Inflammatory bowel disease remains a significant challenge in clinical settings. This study investigated the therapeutic potential of sea cucumber ovum hydrolysates (SCH) in a dextran sulfate sodium (DSS)-induced colitis mouse model. SCH, defined by its elevated stability and solubility, with a molecular weight below 1000 Da, significantly alleviated DSS-induced colitis, as evidenced by enhanced splenic index, reduced colonic damage, and diminished serum pro-inflammatory cytokines. Furthermore, macrogenomic analysis demonstrated that SCH increased beneficial gut microbes and decreased pro-inflammatory bacteria. Furthermore, metabolomic analysis of colonic tissues identified elevated levels of anti-inflammatory metabolites, such as Phenyllactate, 2-Hydroxyglutarate, and L-Aspartic acid, in colitis mice after oral administration of SCH. In conclusion, SCH represents a promising candidate for the treatment of colitis.

In this study, we optimized the BECF process parameters by single-factor experiments and response surface methodology (RSM). Additionally, various analytical techniques were employed to determine the volatile flavor compounds, amino acid composition, and peptide sequences of the fermented product. The antioxidant activities of 10 peptides were evaluated via free radical scavenging assays. The results indicated that the optimal BECF conditions for Apostichopus japonicus body wall (AJBW) were as follows: 2.3 % bacterial inoculum, fermentation for 31 h at 30 °C, 463 U/g enzyme dosage, and enzymatic hydrolysis at 50 °C for 4 h. Gas chromatography-ion mobility spectrometry analysis revealed a significant reduction in aldehydes, which impart a pungent odor, in the co-fermented product (AJM) as compared to the control. While the content of alcohols, ketones, and esters, which contribute to aromatic flavors, was significantly increased. The content of essential amino acids in AJM, as analyzed through an automatic amino acid analyzer, was slightly higher compared to that in AJBW. Liquid chromatography-tandem mass spectrometry identified a total of 808 sea cucumber peptide fragments with high confidence. DPPH, ABTS, and hydroxyl radical scavenging assays revealed that peptides LFW and LFPW exhibited the strongest antioxidant activities. Molecular docking studies showed significant hydrogen-bonding interactions. In conclusion, BECF is an effective strategy for enhancing the flavor of A. japonicus peptide.

Alginate oligosaccharides prepared by alginate lyases attracted great attention because of their desirable biological activities. However, the hydrolysis products are always a mixture of oligosaccharides with different degrees of polymerization, which increases the production cost because of the following purification procedures. In this study, an alginate lyase, Alg4755, with high product specificity was identified, heterologously expressed, and characterized from Vibrio alginolyticus S10, which was isolated from the intestine of sea cucumber. Alg4755 belonged to the PL7 family with two catalytic domains, which was composed of 583 amino acids. Enzymatic characterization results show that the optimal reaction temperature and pH of Alg4755 were 35 °C and 8.0, respectively. Furthermore, Alg4755 was identified to have high thermal and pH stability. Moreover, the final hydrolysis products of sodium alginate catalyzed by Alg4755 were mainly alginate disaccharides with a small amount of alginate trisaccharides. The results demonstrate that alginate lyase Alg4755 could have a broad application prospect because of its high product specificity and desirable catalytic properties.

In this study, polysaccharide extract was prepared from Apostichopus japonicus spermary and purified by ion-exchange chromatography and gel filtration chromatography. Two main fractions named SPSS1 and SPSS2 were obtained and analyzed by ultraviolet spectroscopy and mixed with KBr, respectively. Chemical components analysis proved that SPSS1 and SPSS2 were rich in sulfate. Monosaccharide analysis indicated that in addition to the high content of lactose in both kinds of polysaccharides, the highest content of monosaccharide in SPSS1 was galactose, while in SPSS2 it was fucose. Further, the antitumor study of SPSS1 was carried and the results showed that SPSS1 treatment inhibited the proliferation of HepG2 cells. Through the iTRAQ-based proteome analysis, there were 208 differential proteins between control tumor cells and SPSS1 treatment of tumor cells. Compared to control tumor cells, 135 proteins were upregulated and 73 proteins were downregulated in treatment tumor cells. Practical applications Our study suggested that polysaccharide from sea cucumbers had the potential to be further developed as antitumor drugs.