Effect Of Low Temperature Plasma On Black Resistance And Freshness Quality Of Penaeus Vannamei

As a new type of food preservation and sterilization technology,low temperature plasma technology has been paid more and more attention and utilization.The effects of low temperature plasma on the enzyme activity and secondary structure of commercial purified polyphenol oxidase were studied,and the effects of low temperature plasma on black resistance and freshness quality of Penaeus vannamei were studied.The changes of sensory quality,enzyme activity,nutrient composition,chromatic aberration,texture,flavor,muscle microstructure,volatile base nitrogen,total colony count and water holding capacity were determined before and after treatment with low temperature plasma.Finally,it was concluded that the low temperature plasma could reduce the spatial conformation of polyphenol oxidase,reduce the enzyme activity,delay the blackening,keep the freshness quality,and have no effect on the nutrient composition.The findings are as follows:1.The commercial purification of polyphenol oxidase by low temperature plasma treatment has remarkable effect on reducing enzyme activity.With the increase of the treatment voltage(0-30kv),the enzyme activity decreased gradually,and the enzyme activity decreased with the increase of the treatment time(0-120s).From the point of view of experimental conditions and cost saving of enterprises,the optimum conditions for treatment of polyphenol oxidase were 60 s、30 kV.At the moment,the activity of polyphenol oxidase decreased significantly.In the study of the kinetics of polyphenol oxidase reaction,the rate of enzyme reaction increased with the increase of substrate concentration,which was in accordance with the law of Michlet equation.By means of circular dichroism analysis,α-helix content decreased 3.56%,β-rotation angle content increased 0.81%,β-fold content increased 1.25% and irregular curl content increased 1.50% before and after low temperature plasma treatment.The secondary structure of polyphenol oxidase changed.The enzyme activity was decreased.2.In the storage process of Penaeus vannamei under low temperature plasma treatment,the sensory score of black change increased in both groups,but the rising speed of the treatment group was slower than that of the control group,and the control group reached complete black change at about 6 days.The prawns treated with low temperature plasma had a complete blackening at about 7 days.In the study of the enzyme activity of polyphenol oxidase extracted from Penaeus vannamei,the two groups showed a trend of decreasing first and then increasing continuously,but the change trend of treatment group was lower than that of control group.The enzyme activity of the control group was 7.2 U on the 8th day of storage,but the enzyme activity of the treatment group was 5.8 U,so the blackening phenomenon was delayed to some extent.In the storage process of Penaeus vannamei,all of them will appear blackening and spoilage.The study shows that the rising trend of these indexes of Penaeus vannamei treated by low temperature plasma is lower than that of the control group.On the 4th day,the total number of TBC in the control group rose to 6.3,reaching and exceeding the upper limit of the specified secondary freshness index of Penaeus vannamei,and the TBC of the treatment group reached 4.6,which was the first degree of freshness.In order to study the changes of volatile base nitrogen content in shrimp during storage,the TVB-N content of the control group was 0.683 mg / g on the 10 th day of cold storage,while the TVB-N content of the treatment group was only 0.431 mg / g.3.Compared with untreated Penaeus vannamei treated by low temperature plasma,there were no significant changes in sensory,nutritional composition and quality of Penaeus vannamei compared with untreated Penaeus vannamei.In the storage stage,with the increase of storage time,the sensory organs of the two groups decreased,the nutrients lost,the structure of shrimp bodies deteriorated,but the shrimp treated by low temperature plasma were lower in the degree of deterioration than the control group.The sensory score of the shrimp treated by low temperature plasma was higher than that of the control group,and the shelf life of the treated group was 6 days,which was 2 days longer than that of the control group,and the water content,water holding capacity,protein content,fat content,color,elasticity,moisture content,water holding capacity,protein content,fat content,color and color were increased.Compared with the control group,chewiness and other aspects have a good maintenance effect.By analyzing the scanning electron microscope(SEM)of muscle tissue,it can be concluded that the structure of muscle fiber of Penaeus penaeus treated by low temperature plasma is complete and uniform,the gap of muscle fiber is not large,and the microstructure of muscle is better.The PCA analysis of Penaeus vannamei showed that there was no significant difference between the two groups in the content of volatile flavor compounds,which indicated that the effect of low temperature plasma treatment on the smell was not significant.