Effects Of Endogenous TGase And Konjac Gum On Gel Properties Of Litopenaeus Vannamei

The effects of endogenous TGase and Konjac gum（KGM）on the quality of minced shrimps prepared from Litopenaeus Vannamei were investigated during short-term cryopreservation and thermal gelation.The study was determined that KGM had good anti-freezing effect and improved gel properties of shrimp surimi.In order to clarify the interaction mechanism between KGM and shrimp surimi,the myofibrillar protein（SMP）in shrimp surimi was extracted to prepared the composite gels of KGM and SMP（and shrimp surimi）.The effects of KGM addition amount and molecular weight on the rheological properties and gel properties of the composite gel system were explored.The results were presented as following:（1）The effects of TGase and KGM on the quality of shrimp surimi during short-term frozen storage were analyzed.The results showed that the optimal temperature and p H of endogenous TGase of Litopenaeus Vannamei were 20℃ and 8.0,respectively,and the activity was high in the range of p H 8.0-10.0.K⁺increased the activity of the enzyme,while Cu²⁺,Mn²⁺,Ba²⁺,Fe²⁺,Mg²⁺inhibited the activity of the enzyme to varying degrees,and Cu²⁺would even lead to enzyme inactivation.Endogenous TGase could effectively induce the cross-linking reaction of myosin heavy chain.Ca²⁺could activate endogenous TGase,while EDTA inhibited TGase-induced cross-linking reaction of myosin heavy chain by chelating Ca²⁺.The addition of EDTA to fresh minced shrimp affected its gel properties,while no significant changes were observed in frozen shrimp paste after 14 days with the absence and presence of EDTA.The additions of KGM and antifreeze could significantly suppressed the degradation of myosin heavy chain,and the decrease of total sulfhydryl,free sulfhydryl content and ATPase activity of shrimp paste during frozen storage.The above results showed that TGase had no significant effects on the quality of minced shrimp during short-term frozen storage.In contrast,KGM had better anti-freezing effect and could improve the quality and gel properties of minced shrimp.（2）Based on the above results,KGM was mixed with SMP（and shrimp surimi）to further study the effects of KGM on the gel properties of SMP（and shrimp surimi）.KGM was added to SMP,and the results showed that the surface hydrophobicity,turbidity and particle size of SMP and SMP-KGM composite system increased with the increase of KGM addition.The rheological analysis results showed that SMP and SMP-KGM composite systems both appeared shear thinning phenomenon,and the SK20 had the highest G’value and the best gel structure stability Infrared spectrum analysis showed that the SMP and SMP-KGM composite system had similar spectral characteristics,indicating that there was no obvious group formation.SDS-PAGE analysis showed that the addition of KGM did not cause significant changes in protein bands.Compared with the unheated group,the bands of myosin heavy chain,paramyosin and actin in the heated sample were gradually disappeared,indicating that heating could promote the thermal polymerization among the myofibrillar proteins.SEM and fractal dimension analysis showed that the addtion of KGM could greatly promote the formation of compact and orderly gel structure in SMP-KGM composite system.To further investigate the effects of different KGM additions on the quality of shrimp surimi,KGM was then added to shrimp paste to prepare shrimp surimi gel.The results showed that the addition of KGM could effectively improve the gel properties of shrimp surimi and achieved in the gel properties with the content of 1%.The chemical interaction analysis showed that KGM could promote the formation of the hydrophobic bonds of myofibrillar proteins during gelation process.（3）Three KGMs with different molecular weights were prepared by enzymatic hydrolysis,and the effects of KGMs with different molecular weights on the rheological properties and gel properties of SMP-KGM composite system were investigated.The results showed that with the decrease of KGM molecular weight,the surface hydrophobicity,turbidity and particle size of SMP-KGM composite system decreased to varying degrees.By contrast,medium molecular weight KGM can improve the rheological properties of SMP-KGM composite gel and form a more stable gel structure.The gel properties of shrimp surimi incorporated with degraded KGM addition were lower than those with natural KGM,that was ascribed to the strong water holding capacity and filling effect of natural KGM.Among the degraded KGM groups,the sample with the presence of moderately degraded KGM resulted in the best gel properties,indicating that moderately degraded KGM could produce synergistic effect with SMP,and then form a stable gel system.