The Impact Of Change In Intramuscular Connective Tissue On Texture Of Ice-stored Grass Carp (Ctenopharyngodon Idella) Fillets

Texture is one of the import factors influencing consumer preference.Muscle is encapsulated by intramuscular connective tissue(IMCT)layer.IMCT plays a major role in muscle integrity and has critical importance in maintaining the stability of muscle texture,while systematic investigation of the impact of IMCT on texture is lacking.This study was aimed at clarifying the relationship between degradation of IMCT and softening of grass carp(Ctenopharyngodon idella)fillet during ice storage,determining the role of IMCT in softening of ice-stored grass carp fillet,including the effects of degradation of IMCT and myofibrils on texture deterioration and providing the pattern of the endogenous enzymes on degradation of IMCT.Firstly,the relationship between the degradation of IMCT and the texture deterioration of dorsal muscle of grass carp during ice storage was studied by measuring crucial proteins content,crucial proteins degradation,structure of IMCT and shear force.The results showed that the decorin degraded rapidly in the first 3 days to 43.10%.Meanwhile,pore walls in IMCT showed a rough surface.The degradation of elastin mainly occurred in the first 6 days to 54.24%,while the honeycomb structural of IMCT was collapsed,spalling with holes.The degradation of collagen mainly occurred in the first 10 days to 53.14%,while the honeycomb structural was collapsed completely.The decrease of shear force mainly occurred in the first 10 days while was 63.53% of original value.There was a significantly positive correlation between shear force and IMCT degradation(p < 0.01).Secondly,the role of crucial proteins in maintaining texture stability was established.Exogenous collagenase was used to establish an model of IMCT disruption.Moreover,cathepsin inhibitor(E-64),collagenase inhibitor(texifolin)and complex inhibitor were added to the fish by soaking method,to explore respective impact of myofibrils and IMCT on shear force decrease.The results showed that collagenase was quite effective for destruction of IMCT,while myofiber tissue were not affected.Shear force value became 1.36-folds lower in collagenase group than that in control group while decorin,elastin and collagen became 1.22-folds,1.47-folds and 1.48-folds lower respectively,indicating a quite important role of IMCT in maintaining fish texture.E-64 and texifolin could inhibit myofibrils and IMCT degradation,respectively.There was no significant decrease in shear force in the “E-64 + texifolin” group,indicating the reason of decrease in shear force was mainly due to the degradation of myofibrils and IMCT.And the E-64 treatment group can effectively slow down the decrease of shear force during the first 5 days while the shear force value in E-64 treatment group increased by 66.08%.At the same time,the texifolin treatment group can effectively slow down the decrease of shear force throughout storage period while the shear force value increased by 51.90%,indicating texture deterioration during the primary stage of storage appeared to be caused by destruction of myofibrils and collapse of IMCT and collapse of IMCT was the leading cause of texture deterioration at a later storage.Furthermore,the pattern of the endogenous enzymes on degradation of IMCT were explored.Decorin was removed after deconjugation with ?-glucuronidase and the degradation of elastin and collagen were analyzed by SDS-PAGE and western blotting.The results showed that the removal of decorin lead to an accelerated degradation of collagen and elastin while elastin and collagen degradation levels were significantly increased 1.42-and 1.06-folds,respectively,indicating matrix metalloproteinase including collagenase was involved in the degradation of decorin firstly and then degraded elsatin and collagen.In this study,the relationship between the degradation of IMCT and the degradation of fish texture were systematically investigated.This paper will provide an important theoretical guidance for solving the technical problems of the industrialization of freshwater fish preservation,and this has major implications for reducing wastage,reducing cost and increasing income of fisherman.