Effects Of Stress During Slaughtering On Muscle Freshness And Textural Properties Of Blunt Snout Bream(Megalobrama Amblycephala) During Cryopreservation

In this paper,blunt snout bream(Megalobrama amblycephala)was used as the experimental animal.The effects of two slaughter methods both instant hit(Hit group)and suffocation by exposure to air(Suffocate group)on freshness and texture properties of muscle cryopreservation was investigated.The stress level of the fish during slaughter was first observed by comparing the fish serum cortisol concentrations in percussion and asphyxia groups.The effect of slaughter method on fish muscle quality and freshness was observed by comparing the serum biochemical indicators,serum nucleotide association products,muscle color and p H.In addition,the muscles collected from above tests were also frozen by-20℃ to explore the effect of lethal methods on fish cryopreservation.The experiment was divided into five-time nodes,including cryopreservation at 0,2,4,6 and 8days,and the nucleotide association products,texture properties,and total antioxidant capacity of their muscles were examined.The results are as follows:1.Compared with the Hit group,the suffocation method caused extremely significant increase in the serum cortisol of the blunt snout bream(P < 0.01).The Lactic acid content in the serum of the Suffocation group was also significantly higher than another(P < 0.05).These results suggest that blunt snout bream slaughtered by suffocation were more stressed than those killed by tapping.2.The nucleotide-related products of cryopreserved muscle showed that ATP,ADP,AMP,Hx R and Hx of the Hit group were higher than those of the Suffocation group at 0d.After 6 days in the freezer,no ATP was detected in the muscles of the two methods which indicating the muscle energy is basically exhausted at this time.The IMP content in the muscle of the Suffocation group was significantly higher than Hit group(P < 0.01)which indicating the muscle of the Suffocation group degraded from ATP to IMP faster than the Hit group.The K value of blunt snout bream in the Hit group was lower than that in the Suffocation group,indicating that the blunt snout bream in the Hit group had better muscle freshness than Suffocation group.3.On the day of slaughter,the shear force,hardness,springiness,cohesiveness,gmminess,chewiness and resilience of the muscle of Hit group were significantly higher than Suffocate group(P < 0.01).During the 0-8 days of cryopreservation,the shear force and texture properties of the muscle of Hit group were higher than Suffocate group.On the2 d and 4d,the muscle cohesion and viscosity of the Hit group were significantly higher than Suffocate group(P < 0.05).From the analysis of muscle texture properties,the muscle quality of fish in Hit group was significantly better than Suffocate group.On the2 nd to 8th day of cryopreservation,the texture properties of muscles were significantly lower than the first day of slaughter.The results showed that slaughter stress had a negative impact on muscle preservation and quality of the blunt snout bream.Compared with the two slaughter methods,the stress level of fish in the Suffocate group was significantly higher than Hit group.During cryopreservation at-20℃,the muscle texture properties and freshness of fish in Hit group were better than Suffocation group.With the prolongation of storage time,the muscle quality of fish treated by both slaughtering methods decreased significantly.It recommend that the frozen storage time of blunt snout bream at-20℃ should be within 4 days.This research concluded the difference of slaughter methods between instant hit and suffocation by exposure to air.In addition,these results also provide a reference for fresh-keeping of fish and protection of fish welfare.