Simultaneous Detection Of Free Amino Acids And Glutathione In Shrimps And Its Application

Shrimps are rich in amino acids,proteins,trace elements and minerals.It is one of the food sources of excellent protein.It has a wide range of varieties and is the main aquatic products loved by consumers.The flavor characteristics of free amino acids and their changes under different storage conditions have an important impact on the taste,quality and freshness of food.Free amino acids,which are abundant in shrimp,are an important component of the flavor of shrimp products.Glutathione has physiological functions such as scavenging free radicals,anti-aging,participating in immune regulation and amino acid metabolic transport.In this paper,three aspects were studied,including the optimization of the extraction of free amino acids in shrimp,the establishment of a method for simultaneous detection of free amino acids and glutathione in shrimp,and the correlation analysis between free amino acids and glutathione and quality in shrimp(Penaeus vannamei and Macrobrachium nipponense)during low temperature storage conditions.The specific contents and conclusions are as follows:1.The nutrient composition,amino acid composition and nutritional value of the muscles and heads of different marine prawn(Penaeus vannamei,Penaeus monodon,Parapenaeus fissuroides)and freshwater shrimps(Macrobrachium nipponense,Exopalaemon modestus,Macrobrachium rosenbergii)were analyzed.The extraction effects of different concentrations of extractants(3～20%trichloroacetic acid,30～70%ethanol and 3～12%sulfosalicylic acid)on free amino acids in Penaeus vannamei and Macrobrachium nipponense were compared,and different ultrasonic extraction conditions(ultrasonic power,time,temperature and material to liquid ratio)were optimized by single-factor and response surface methods to determine the optimal extraction process of free amino acids in both shrimps.The results were as follow:Met+Cys,Lys and Val were the main limiting amino acids of six kinds of shrimp muscle;Lys,Val and Ile are the main limiting amino acids of six shrimp heads.Both shrimp meat and shrimp head,the essential amino acid nutritional value of Macrobrachium nipponense was the highest among the three freshwater shrimps,and the essential amino acid nutritional value of Penaeus vannamei was the highest among the three marine prawns.12%trichloroacetic acid was used as the extracting agent,and the optimal ultrasonic assisted extraction method of free amino acids from shrimp was 250 W power,22±2℃ultrasonic temperature,25 g/m L material to liquid ratio,and 17 min ultrasonic time,the total free amino acid content of Penaeus vannamei was 5591.35±12.84 mg/100g(predicted value 5503.84 mg/100 g)and the total amount of free amino acids of Macrobrachium nipponense was 3480.13±16.73 mg/100 g(predicted value 3413.57mg/100 g)in 13 min ultrasonic time.The influencing factors are as follows:material liquid ratio(29)ultrasonic time(29)ultrasonic power(29)ultrasonic temperature.2.A rapid and stable automatic amino acid analysis method was developed for the simultaneous determination of free amino acids and glutathione in different shrimps(Penaeus vannamei,Penaeus monodon,Exopalaemon modestus,Macrobrachium nipponense).When the sodium citrate buffer B1 contains 135 m L/L ethanol,7 m L1mol/L sodium hydroxide and the conversion time between B2 and B3 was 5.6 min,glutathione and 20 amino acids such as Tau,Orn,Hyp could be separated effectively in30 min.The developed method showed good linearity(R~2≥0.9991)in the range of1～250μg/m L with good intra-day and inter-day precision(relative standard deviations≤2.38%)and spike recovery(86.42～103.64%).GSH and Cys were used to identify marine prawn and freshwater shrimp.Hyp can be used to distinguish Penaeus vannamei and other shrimps,while the content of Ser can be used to distinguish Macrobrachium nipponense and other shrimps.The highest content of the total FAAs was found in Penaeus vannamei,and principal component analysis revealed that Penaeus vannamei had the highest comprehensive score for FAAs and GSH.Arg and Gly were found to have the greatest influence on shrimp flavor.3.The correlation between changes in FAAs and GSH and changes in p H,TVB-N,TBA and textural changes in Penaeus vannamei and Macrobrachium nipponense during storage at different temperatures(-3°C and 4°C)was studied.The results showed that the changes of Pro,Glu,Arg,Orn and flavor amino acids of Penaeus vannamei during storage were most significant;Arg,Glu,essential amino acids and flavoring amino acids in the Macrobrachium nipponense have the most significant changes,and-3℃partial freezing is helpful to maintain the good flavor of Penaeus vannamei and Macrobrachium nipponense.The content of GSH in Penaeus vannamei increased first and then decreased with the prolongation of storage time,reaching the highest value after 4 days at 4℃and10 days at-3℃,respectively.According to the changes of quality,FAAs and GSH,it can be obtained that the best consumption time of Penaeus vannamei is 4 days and that of Macrobrachium nipponense is 2 days during 4℃cold storage,while that of is 15days and 10 days for these two shrimp during-3℃partial freezing,respectively.Orn is significantly correlated with the quality of Penaeus vannamei and Macrobrachium nipponense under different storage conditions.Therefore,Orn can be used as the characteristic free amino acid of these two kinds of shrimp to evaluate freshness during storage.