Changes of collagen in sea cucumber (Stichopus japonicas) during cooking

Characteristics of the Intestine Extracts and Their Effect on the Crude Collagen Fibers of the Body Wall from Sea Cucumber Apostichopus japonicus

Sea cucumbers Apostichopus japonicus will vomit their intestines during certain stimulations, and the collagen of the body wall will then be degraded. To define the effect of the sea cucumber intestine extracts on the body wall, the intestinal extracts and crude collagen fibers (CCF) of sea cucumber A. japonicus were prepared. According to the gelatin zymography, the type of endogenous enzymes in intestinal extracts were mainly serine endopeptidases with optimal activities at pH 9.0 and 40 °C. According to the rheology results, the viscosity of 3% CCF decreased from 32.7 Pa·s to 5.3 Pa·s by adding intestine extracts. The serine protease inhibitor phenylmethanesulfonyl fluoride inhibited the activity of intestinal extracts and increased the viscosity of collagen fibers to 25.7 Pa·s. The results proved that serine protease in the intestinal extracts participated in the process of body wall softening in sea cucumbers.

Rheological properties, thermal stability and conformational changes of collagen from sea cucumber (Apostichopus japonicas)

Sea cucumber collagen (SCC) properties affected the thermal processing of sea cucumber. SCC showed the shear-thinning and pseudo-plastic properties, and the viscosity and frequency of viscoelastic crossover were decreased gradually with the temperature from 15 to 30 °C. Differential scanning calorimetry of SCC confirmed that it was thermolabile with the increase of temperatures, acid or NaCl concentrations. As the temperature increasing, the triple helix of SCC disappeared with the decrease of the relative proportion of P2 structures by circular dichroism spectrometry and Fourier transform infrared spectroscopy, and shearing could accelerate the change. Intramolecular changes investigated by molecular dynamics simulation showed the average number of hydrogen bonds decreased from 47 (20 °C) to 42 (80 °C), indicating triple helix of SCC was triggered to uncoil within 250 ns. These results could provide a scientific basis for processing of sea cucumbers.

Sea Cucumber Derived Type I Collagen: A Comprehensive Review

Collagen is the major fibrillar protein in most living organisms. Among the different types of collagen, type I collagen is the most abundant one in tissues of marine invertebrates. Due to the health-related risk factors and religious constraints, use of mammalian derived collagen has been limited. This triggers the search for alternative sources of collagen for both food and non-food applications. In this regard, numerous studies have been conducted on maximizing the utilization of seafood processing by-products and address the need for collagen. However, less attention has been given to marine invertebrates and their by-products. The present review has focused on identifying sea cucumber as a potential source of collagen and discusses the general scope of collagen extraction, isolation, characterization, and physicochemical properties along with opportunities and challenges for utilizing marine-derived collagen.

Collagen fibrils of sea cucumber (Apostichopus japonicus) are heterotypic

Sea cucumbers attracted increasing interest due to its nutritional functions. Collagen is the most important structural biomacromolecule in sea cucumber body wall, and is highly related to the textual properties and food quality of sea cucumber. In this study, the type of constituent collagens of sea cucumber collagen fibrils was investigated, employing a commercially important species Apostichopus japonicus as the material. Proteomics and bioinformatics analysis revealed that collagen fibrils of A. japonicas are heterotypic. Two clade A and one clade B fibrillar collagens and two FACIT collagens were identified from the fibrils. Besides, the heterogeneity was also revealed in the pepsin-solubilized collagen (PSC) of A. japonicus by using the proteomics strategy. It implied that the previous conclusions on the type of sea cucumber collagen deduced from SDS-PAGE analysis should be rechecked. The results provided novel insight into the composition of sea cucumber collagen fibrils.

RNA Sequencing Analysis to Capture the Transcriptome Landscape during Tenderization in Sea Cucumber Apostichopus japonicus

Sea cucumber (Apostichopus japonicus) is an economically significant species in China having great commercial value. It is challenging to maintain the textural properties during thermal processing due to the distinctive physiochemical structure of the A. japonicus body wall (AJBW). In this study, the gene expression profiles associated with tenderization in AJBW were determined at 0 h (CON), 1 h (T_1h), and 3 h (T_3h) after treatment at 37 °C using Illumina HiSeq™ 4000 platform. Seven-hundred-and-twenty-one and 806 differentially expressed genes (DEGs) were identified in comparisons of T_1h vs. CON and T_3h vs. CON, respectively. Among these DEGs, we found that two endogenous proteases-72 kDa type IV collagenase and matrix metalloproteinase 16 precursor-were significantly upregulated that could directly affect the tenderness of AJBW. In addition, 92 genes controlled four types of physiological and biochemical processes such as oxidative stress response (3), immune system process (55), apoptosis (4), and reorganization of the cytoskeleton and extracellular matrix (30). Further, the RT-qPCR results confirmed the accuracy of RNA-sequencing analysis. Our results showed the dynamic changes in global gene expression during tenderization and provided a series of candidate genes that contributed to tenderization in AJBW. This can help further studies on the genetics/molecular mechanisms associated with tenderization.

Fucosylated chondroitin sulfate is covalently associated with collagen fibrils in sea cucumber Apostichopus japonicus body wall

Fucosylated chondroitin sulfate (fCS) is the major carbohydrate constituent of sea cucumber. However, the distribution of fCS in the sea cucumber body wall has not been fully described. We addressed this in the present study employing Apostichopus japonicus as the material, a sea cucumber species with significant commercial importance. It was found that fCS was covalently attached to collagen fibrils via O-glycosidic linkages. Transmission electron microscopy analysis revealed that fCS precipitate was present in gap regions of collagen fibrils as roughly globular or ellipsoidal dots. The fCS dots arranged circumferentially around the fibrils with an axial repeat period that matched the periodicity of the fibrils. Physicochemical analysis indicated that the presence of fCS significantly increased the negative charge of the fibrils. These findings provide novel insight into fCS distribution in the sea cucumber body wall and its supramolecular organization with other macromolecules.