Changes Of Collagenous Tissue In Body Wall Of Autolytic Sea Cucumber Stichopus Japonicus

Sea cucumber is a kind of important marine economic animal. In 2013, the total Chinese output of sea cucumber was about 193.7 thousand tones, and the industrial output value was about RMB 50 billions Yuan by estimated. Sea cucumber is very susceptible to external stimulus. In response to external stimulus, the body of sea cucumber relaxed, mucoid degeneration took place, and part of the initially firm body wall even flowed out in a sticky mass. Such massive tissue autolysis can lead to severe postharvest deterioration in quality of sea cucumber, consequently cause heavy economic losses. In the present study, the autolysis of sea cucumber(Stichopus japonicas) was induced by UV irradiation, the microstructural changes in Stichopus japonicus body wall were investigated through light microscopic examination of tissues by Van Gieson’s(V-G) staining, and the ultrastructural changes in collagenous tissue of Stichopus japonicus body wall were investigated through scanning electron microscopy(SEM) and transmission electron microscopy(TEM). Meanwhile, the hydroxyproline level, sugar level, amino acid composition, as well as molecular weight distribution(MWD) of the soluble component were investigated by UV spectrophotometry and HPLC. Through this study, we revealed the structural foundation of autolysis of Stichopus japonicas.In response to UV irradiation, the body of Stichopus japonicus relaxed, mucoid degeneration took place, and part of the initially firm body wall even flowed out in a sticky mass. Under light microscopy(LM), the skin of fresh Stichopus japonicus was intact, and the fiber network was clear, uniform arrangement; after autolysis, the cuticle was broken, and the fiber network feature of dermis became blurred and thin. Under SEM, the collagen fibers in body wall of fresh Stichopus japonicas arranged orderly, neat structure; after autolysis, collagen fiber depolymerized into fibril. Under TEM, the characteristic D-period structure of fibril in the body wall of fresh Stichopus japonicas was clear; after autolysis, it became fuzzy. It was speculated that part of fibril uncoiled.The analysis of the water-soluble substances of body wall of Stichopus japonicas showed that the amount of the water-soluble substances increased slightly with the extension of autolytic time at the initial stage, and it increased significantly when mucoid degeneration took place. The change of dissolving amount of glycosaminoglycans during autolysis showed a similar pattern with that of the water-soluble substances. During the whole autolysis processing, hydroxyproline has not been detected in the water-soluble substances by Woessner method and HPLC method, which suggested that soluble collagen components did not be produced in the process of autolysis. SDS-PAGE analysis of the water-soluble substances showed that there was no strip of collagen subunits. However, in SDS-PAGE, a new stripe with molecular weight of about 116 k Da appeared when mucoid degeneration took place. HPLC-gel analysis indicates that the MWD of the water-soluble substances changed slightly.In summary, during autolysis of Stichopus japonicas, collagen fiber in body wall depolymerized into fibril during autolysis, and part of fibril uncoiled. However, the evidence of change of structure of collagen molecules has not been detected. Thus it was speculated that the autolysis in body wall of Stichopus japonicas was mainly caused by the dissolution of non-collagen proteins and the depolymerization of collagen fibers.