Research On Post-slaughter Muscle Characteristics And Quality Improvement Technology Of Sea Bass

Sea bass（Lateolabrax japonicus）is rich in protein,polyunsaturated fatty acids,vitamins and minerals.At the same time,it is a good source of EPA and DHA for consumers.Sea bass is popular among consumers because of its white flesh and fresh taste.Sea bass is an essential and economical fish in China,and its production has increased year by year in recent years,ranking second in the production of marine fish culture in China.The national production of sea bass increased by about 24.00%in 2020 compared to 2017.Sea bass has the following problems:1)the meat is garlic-like,has a low flake rate,and is extremely easy to disperse when encountering boiling water,2)the disadvantages of fresh sea bass with a strong sense of slag and poor palatability,and 3)heavy fishy odor.The series of problems directly influenced the consumer’s purchasing desire and eating experience while blocking the development of the industry.Therefore,it is necessary to study and solve these drawbacks.In this study,firstly,the effects of the slaughter method and post-slaughter treatment temperature on the quality of sea bass were investigated.Then,the effect of different slaughtering methods on the volatile components of raw and the cooked sea bass was identified and analyzed using electronic nose（E-nose）and gas chromatography-ion mobility spectrometry（GC-IMS）techniques.Researched and developed compound quality improvers for small flakes and determined optimal process ratios by response surface methodology.Studied the tenderization process of sea bass by orthogonal experimental method and obtained the final phosphorus-free compound tenderizer.The main findings are as follows.1.The effects of slaughter method and post-slaughter treatment temperature on the quality of sea bass were elucidated:Head shot control stun death（HSD）,Bloodletting to death slaughter（BDS）and Ice Faint to death（IFD）were studied.The effects of slaughter methods on the pH,color difference,texture,shear force,Myofibril fragmentation index（MFI）,myofibril protein surface hydrophobicity,microstructure and organoleptic scores of sea bass at-80℃,0℃,15℃and 25℃.The results showed that the slaughtering method significantly affected the quality of sea bass（P<0.05）and that the HSD slaughtering method was better than the IFD and BDS slaughtering methods.The surface hydrophobicity of the BDS group was greater than that of the IFD and HSD groups,with low post-mortem hardness,poor chewiness,high shear force,and a taut,overly dense microstructure;the hardness,chewiness and elasticity of the IFD group were not significantly different from those of the HSD group（P>0.05）,but shear force values were high.The microstructure showed a rough,cottony surface of the myogenic fibers,with a lower sensory score.Post-slaughter treatment temperature significantly affected the quality of sea bass,with 0℃having a positive effect on the post-slaughter quality of sea bass and-80℃,15℃and 25℃having a negative effect.Compared to 0℃,-80℃produced ice crystals in the fish,resulting in higher hydrophobicity of myogenic fiber proteins,-80℃slowed down the process of post-mortem stiffness and maturation,and the fish fibers appeared taut and overdense;at 15℃and 25℃,the treatment temperature resulted in higher hydrophobicity of myogenic fibers,uneven arrangement of myogenic fibers,excessive inter-fibre gaps,lower a^*values and lower overall sensory scores.At 25℃,the hardness and chewiness are low,the myofibrils are disorganized,cottony,or broken,and the myofibrils are ruptured.0℃is low hydrophobicity,good tenderness,hardness,chewiness and a high overall sensory score.Therefore,0℃is suitable for post-slaughter processing.It is recommended that sea bass can be slaughtered by the HSD method and then matured at 0℃before being frozen at-80℃.2.The temperature significantly affected fish quality（p<0.05）,with a positive effect only at 0°C.As the temperature increased,pH in the BDS group,hardness in the HSD group,chewiness in all groups first increased and then decreased,hydrophobicity in the HSD and BDS groups first decreased and then increased,hydrophobicity in the IFD group increased,shear force,sensory score,pH and a^*values in the IFD group decreased,MFI values increased,myofibrillar proteins changed from taut,overdense and cotton wool-like to unevenly arranged with excessive gaps,rupture of myofibrillar membranes,b^*and elasticity did significantly No significant changes in b^*and elasticity.Therefore,0°C is suitable for post-slaughter cooling.It is recommended that sea bass can be slaughtered by the HSD method and then matured at 0°C before being frozen at-80°C.1.The effects of slaughter methods on the volatile compounds of sea bass were investigated,and there were significant differences in flavor components between raw and cooked fish.There were 31 volatile components in the raw group,and 39 volatile components were detected in the steamed group.Two new aldehydes（（E）-2-octenal,（E）-2-pentenal）,two alcohols（（E）-2-hexenol,hexanol）and four undetermined volatile flavor components were produced in the steamed group.The fresh sea bass had a heavy fishy odor in the HSD and IFD groups.The Eugenol anesthesia to death slaughter（EAD）group had a strong chemically irritating odor due to the residual eugenol.The BDS group had a slight fishy odor.After steaming,the fishy odor of IFD and HSD groups increased,and the EAD group still had a chemically irritating odor.The BDS group had a solid and pleasant aroma due to the high content of benzaldehyde,2-pentylfuran,（E）-2-octenal and the highest total content of esters.Therefore,as far as fish flavor is concerned,the BDS group is more suitable for slaughtering sea bass.2.The quality improvement process technology of sea bass fillets was studied and established.After the comparative analysis,TG enzyme,gelatin and egg white powder had a noticeable improvement effect.The best process was obtained using response surface methodology to optimize the compound quality improver:TG enzyme 3.90%,gelatin2.40%,egg white powder 6.00%and maceration time 5.50 h.The improved sea bass fillets had improved cooking resistance,white color,unique aroma,and sea bass’s fresh smell,moderate elasticity,and good quality.3.A tenderisation technique for sea bass had developed.A single-factor test was conducted to analyze the effects of papain（PA）mass fraction,fig protease（Ficin,FI）mass fraction,NaHCO₃mass fraction and tenderizing time on the shear force,water retention and sensory quality of sea bass.The optimal formulation of phosphorus-free compound tenderizer was then obtained by the orthogonal experimental method:1.00%mass fraction of NaHCO₃,1.00%mass fraction of PA,2.00%mass fraction of FI,and tenderization time1 h.The microstructure showed that the myogenic myofibers swelled and thickened;the gaps became smaller due to extrusion;the myofibrillar surface membrane was intact without obvious breakage after tenderization.The tenderized fish was juicy and had good color,lubricious taste and a high flake rate.Therefore,this process could significantly improve the tenderness of sea bass,which was beneficial to the further processing and consumption of sea bass.