Study On The Inhibition Mechanism And Quality Of Hypotaurine On The Melanosis Of Penaeus Vannamei

Shrimp is loved by consumers for its nutrition and delicious taste,but its storage life is short.The blackening caused by polyphenol oxidase(PPO)will seriously affect its sensory quality and commercial value.Excessive SO₂ produced by sulfite,a commonly used inhibitor of shrimp blackening,will cause allergic reactions and pose a threat to consumers'health.Therefore,it is very important to seek natural,safe and efficient sulfite substitutes.Hypotaurine(HTU)is a natural product widely found in crustaceans,which can be converted into taurine in human body.Studies have shown that HTU has good oxidation resistance,and shows excellent color protection and preservation effect in the preservation of fruits,vegetables and juices.Hypotaurine has a potential application prospect in the field of aquatic products,especially in delaying the blackening of Penaeus vannamei and improving the storage quality,because of its dual functions of antioxidation and enzymatic browning resistance.Therefore,in this study,polyphenol oxidase extracted from Penaeus vannamei was taken as the research object to explore the effect of hypotaurine on enzyme activity and enzyme conformation,and to clarify its inhibition type and inhibition mechanism.Then,the better application concentration was determined by studying the blackening and other quality changes of Penaeus vannamei during storage after soaking with hypotaurine.Finally,on the basis of soaking and keeping fresh with hypotaurine,it was compounded with chitosan coating to study the changes of shrimp quality during storage,in order to provide theoretical basis for applying hypotaurine to keeping fresh of aquatic products.The main research results were shown as follows:(1)Polyphenol oxidase with molecular weight of 200 k Da was isolated and extracted from the head of Penaeus vannamei,and the specific activity of enzyme solution was 421.4 U/mg.HTU inhibited PPO activity with IC₅₀of 16.09 g/L.The type of PPO inhibition is competitive reversible inhibition,and the inhibition constant K_Iis 0.445 mmol/L.The results of SDS-PAGE showed that the addition of HTU did not change the molecular weight of enzyme and also did not destroy the primary structure of enzyme.The results of circular dichroism showed that the secondary structure of the enzyme changed,and the hydrogen bond of?-helix was destroyed,which exposed the hydrophobic group.The results of surface hydrophobicity showed that HTU could enhance hydrophobicity by changing the secondary structure of PPO.The spectrum of endogenous fluorescence spectrum showed that HTU could quench the intrinsic fluorescence of enzyme,and?_maxwas red-shifted,which affected the tertiary structure of PPO.Totally,it was speculated that the inhibitory effect of HTU on PPO was through binding with the active site of enzyme,which led to the change of enzyme conformation and the decrease of enzyme catalytic activity.(2)Different concentrations(0.1%,0.5%,1%,1.5%and 2%(w/v))of HTU showed a positive correlation with the antioxidant activity.When shrimp was soaked with distilled water at 4?(control group),HTU at 0.1%,1%,2%and sodium metabisulfite(SMS)at 1.25%and stored at 4?for 10 days,compared with the control group,HTU treatment could delay the increase of TVB-N value,pH value and TBA value,and the physical and chemical indexes of prawn meat were better.At the same time,the results of texture and microstructure showed that higher concentration of HTU could reduce the decrease of hardness and springness and maintain the integrity of muscle.In addition,the shrimp treated with 20 g/L HTU had a lower score of melanosis and a better color change.The results showed that HTU could effectively delay the spoilage of prawns under the cold storage condition of 4?,and could effectively reduce the blackening of prawns and maintain good sensory quality.Among them,20 g/L HTU had the best treatment effect and could delay the shelf life of prawns for 3?4 days.(3)The effects of chitosan coating combined with HTU on the melanosis and other quality of Penaeus vannamei stored at 4?for 10 days were studied.Compared with the control group,the melanin production and total color difference of shrimp in chitosan group,HTU group and compound group were obviously slowed down,and the increase of total number of colonies,pH value,TVB-N value and TBA value were significantly inhibited.The melanosis score,total number of colonies,TVB-N value,TBA value and sensory score of shrimp treated with chitosan and HTU were lower than those treated with chitosan and HTU alone,which indicated that there was a synergistic effect between chitosan and HTU.These results indicate that the combination of chitosan and HTU can be used as an effective natural substitute for the synthesis of anti-blackening agent,which can be used to inhibit post-mortem blackening and improve the quality of frozen shrimp.