Protein Oxidation,Cathepsins Activity,Texture And Structure Of Muscle Changes Of Hairtail During Low-temperature Storage

The hairtail(Trichiurus haumela)is rich in resources and nutritional value.It is also delicious,so being favored by consumers.However,owing to its unique requirement of water pressure and the characteristics of vertical swimming,so artificial cultivation can not be carried out and the low-temperature storage technology is mostly used to prolong the shelf life of hairtail.Protein oxidation and endogenous protease are main reasons for quality changes during storage because of hairtail being rich in protein,At present,the mechanism of protein oxidation on texture is still unclear for hairtail.In addition,there are few in-depth studies on the effects of activities of cathepsin,glucosidase(AG enzyme)and N-acetyl-?-D-glucosidase(NAG enzyme)on protein degradation and muscle microstructure of hairtail.Taking the hairtail(Trichiurus haumela)as the research object in the present study,the trend of the indicators of protein oxidation during different low-temperature storage was observed.The changes of biochemical and texture characteristics caused by protein oxidation and the relevance between protein oxidation and the texture of hairtail was analyzed.Moreover,the changes of activities of cathepsin,AG and NAG enzymes during storage was analyzed to elucidate the destructive effects of cathepsin on protein hydrolysis,protein structure and muscle microstructure,and the effects of AG and NAG enzymes on cell integrity.The main results were as follows:(1)The changes of carbonyl,sulfhydryl,surface hydrophobicity,Ca2+-ATPase activity,Mg2+-ATPase activity,TCA-soluble peptides and texture indexs(hardness,springiness,gumminess and chewiness)during storage at 0 ? and 4 ? were measured and the linear correlation between myofibrillar protein oxidation and texture was analyzed.The results showed that more protein oxidation indicated the greater amount of degraded small molecule peptide and the more serious texture deterioration.There was a significant linear correlation between the indicators of protein oxidation and texture of hairtail.Although the degree of protein oxidation and texture of hairtail under 0 ? were lower than those under 4 ?,there was no significant difference between 0 ?and 4 ?.(2)The activity changes of AG,NAG enzymes and cathepsin B,L and H,the degradation of whole,water and salt-soluble proteins,the secondary structure of myofibrillar protein and the microstructural changes of hairtail at 0? and 4? were measured and the internal relationship between them was analyzed.The results showed higher cathepsin B and L activities,which caused the hydrolysis of corresponding proteins,changed the secondary structure of myofibrillar protein and cell integrity,thus deteriorating the muscle tissue of hairtail.It was clarified that cold storage was not suitable for hairtail storage on the basis of enzymology.(3)The hairtail were stored in liquid nitrogen quick freezing and refrigerator freezing conditions at different temperatures for 120 days and the relevance between myofibrillar protein oxidation and texture of hairtail was analyzed.The results showed that umder storage for 60 days,there was no significant changes in the indicators of hairtail frozen in refrigerator after liquid nitrogen freezing.The texture were better when the temperature was lower,which followed by less protein oxidation.There was a significant linear correlation between the indicators of protein oxidation and the texture characteristics.In the later period of storage,the texture of hairtail was changed with the degree of protein oxidation increasing gradually.However,the effect of liquid nitrogen quick freezing was always better than that of refrigerator for hairtail storage.(4)The cathepsin B and L activities could be inhibited by ultra-low-temperature in a short period of time(0-60 days).At the later stage of storage,the inhibition gradually weakened,resulting in the gradual degradation of water-soluble protein and salt-soluble protein,the changes of the orderly and stable secondary structure of myofibrillar protein,the destruction of the structure of muscle fibers of hairtail,the damage of cell integrity,and the increase of AG and NAG enzyme activities.During the whole freezing storage,the indicators of hairtail under quick-frozen with liquid nitrogen were significantly better than that of direct freezing in refrigerator.