Study On The Signaling Before Starting Autolysis Under UVA Irradiation And Oxidate During Thermal Processing In Stichopus Japonicus

As a kind of aquatic products with high nutritional value and health function,sea cucumber has been paid more and more attention by people.However,sea cucumber has strong ability of autolysis,which brought a lot of inconvenience to the transport,processing and storage of them.To enrich the theory of autolysis of sea cucumber and improve the quality of the sea cucumber products,based on sea cucumber（Stichopus japonicus）,two aspects were studied in this paper.On the one hand,the yearling S.japonicus were induced by the UVA then stored in dark at room temperature.To examine the autolysis of S.japonicas,cathepsin L activity and protein degradation situation were researched.To prove whether the cell apoptosis occurred,caspase-3 activity and DNA fragmentation were studied.In order to determine the upstream pathways of starting the autolysis accompanied by apoptosis,under UVA induced,activation of the MAPK family and oxidative stress including reaction reactive oxygen species（ROS）production and antioxidase system damage were analysed.On the other hand,build the model of lipid peroxidation during instant sea cucumber processing by electron spin resonance（ESR）method,and study the effects of various antioxidants to the model and the antioxidant mechanism from the angle of Fe²⁺.The results showed that the basic signal pathway of sea cucumber autolysis induced by UVA were as followed: O₂^.-generated by UVA induction in sea cucumber turned into H₂O and O₂ by superoxide dismutase,catalase and glutathione peroxidase.H₂O₂ as intermediate product turned into HO.by Fenton reaction under the pariticipation of Fe²⁺.The large number of ROS including O₂^.-HO.and H₂O₂ also damaged these antioxidant enzyme and reduced the elimination rate of ROS.Accumulated ROS further induced activation of p38 and JNK,then activated downstream proteolytic enzymes such as caspase-3 and cathepsin L.Activated caspase-3 led to DNA damage,and cathepsin L accelerated structural protein hydrolysis.Lastly,DNA damage and proteolysis resulted in sea cucumber autolysis.S.japonicus guts,body walls from S.japonicus and the yearling S.japonicus under the certain heating conditions produced lipid free radicals.And the generation of lipid free radicals had positive correlation with heating temperature and time.The model of lipid peroxidation during instant sea cucumber processing was built.V_C and two kinds of natural antioxidants expressed peroxidation at low concentration and antioxidation at high concentration.Throug studing the peroxidative role of Fe²⁺,the two-way effects of V_C were found to be related to iron ions.Through studying the basic signal pathway of S.japonicus autolysis induced by UVA,enrich the mechanism of starting autolysis in S.japonicus,and provide a theoretical basis to solve the problems of autolysis during transportation,processing and storage.At the same time,studying lipid peroxidation,the role and mechanism of antioxidants in the S.japonicus during heating process would reduce adverse effects and improve a new research direction to improve the quality of the products.