| Chinese mitten crab (Eriocheir sinensis) is one of farmed aquatic animals in China,whose scale constantly increases. Nowadays, lake crab culture has been substituted bypond culture, because it intensify lake eutrophication. Therefore, improve quality ofpond cultured crab is an urgent problem to be solved to satisfy the market requirement.In order to reveal the difference of sensory characteristics of crab rearing in pond andlake and improve sensory quality of crab rearing in pond, the main work is as follows.1. Carotenoids which is the body color component in the hepatopancreas andcarapace, the taste active compounds, including freea mino acids, flavour5’-nucleotidesfatty acids in the meat and hepatopancreas of Chinese mitten crab (Eriocheir sinensis) aswell as sensory characteristic were compared between crabs from Yangchen lake andponds firstly. We select appendage completed female crab to analyse body colorcomposition and taste active compounds. The method we used are spectrophotometryand chromatography. Results showed that: The concentrations of the carotenoids, FAAs,5’-nucleotides of hepatocrease and muscle were all higher than that of pond crabsignificantly (P<0.05). Saturated fatty acids in pond crab hepatocrease and muscle werehigher than in lake crab and significantly. No significant difference was detected inhepatopancrease MUFA between crab sources, however, that in pond crab muscle waslower than in lake crab significantly (P<0.05). The HUFA in pond crab wassignificantly lower than in lake crab (P<0.05), no matter in hepatopancrease or inmuscle. Results of organoleptic test showed significant different in hepatopancreasecolor,shell color, sweet and umami taste(P<0.05),while no significant difference inmuscle umami taste beween the lake crab and the pond crab(P>0.05). No dislike flavourand taste were detected in both lake and pond crab, no matter in muscle orhepatopancrease. The results suggested that: the concentrations and component of carotenoids, FAAs,5’-nucleotides and Saturated fatty acids were the reason of thedifference. The water quality was the potential factors impact the crab quality.2. According to the ecological difference in ponds and lakes, we speculated thatone of the factors affecting their quality was the lack of exogenous pigment and naturalbait under the condition of the pond. Many microalgae are rich in carotenoid and othernutrients. Therefore we designed experiments to investigate the feasibility of usingmicroalgae to improve sensory quality of crab based on the ecological differences withponds and lakes. We added2%spirulina,3%spirulina,0.35%haematococcus pluvialis,0.55%haematococcus pluvialis,10%alfalfa meal,15%alfalfa meal respectively to thefeed and used no addition as control.420crabs with initial mean weights of8.8±0.1gwere randomly assigned to seven dietary treatments with four replicates and fifteencrabs with each pen. Growth,freea mino acids,flavour5’-nucleotides, fatty acids,Carotenoids in the meat and hepatopancreas and other indicators were analyzed after60days. Results showed that:(1) Groups of2%spirulina, haematococcus pluvialis, alfalfameal can notablely increase the content of carotenoid in liver and shell of crab (P<0.05).There was no significant difference between3%spirulina group and the control (P>0.05)The hyperchromic effect of low addition groups were better than that of high additiongroups.(2) The amino acids that TAV>1in liver were glutamic acid, histidine, lactamine,arginine, valine, methionine, phenyl alanine and lysine; The amino acids that TAV>1inmuscle were glutamic acid, histidine, glycin, lactamine, arginine and lysine. FAAcontent and amino acids that TAV>1in muscle and liver of2%spirulina and0.35%haematococcus pluvialis group were significantly higher than control (P<0.05). FAAcontent in liver and amino acids that TAV>1of3%spirulina were significantly higherthan control (P<0.05), while there were no significant difference in muscle (P<0.05).FAA content in muscle and liver and amino acids that TAV>1of0.55%haematococcuspluvialis group had no significant difference with control (P<0.05). FAA content andamino acids that TAV>1of10%and15%alfalfa meal groups were significantly higherthan control (P<0.05) in liver. FAA content and amino acids that TAV>1of10%alfalfameal group were significantly higher than control (P<0.05) while there were nosignificant difference between15%alfalfa meal group and control (P>0.05) in muscle.(3) The TAV of IMP and GMP in all groups were greater than1while the TAV of AMP was less than1. The content of IMP in2%spirulina,3%spirulina,0.35%haematococcus pluvialis and10%alfalfa meal group were significantly higher thancontrol (P<0.05) while0.35%haematococcus pluvialis group had no significantdifference with control (P>0.05). The content of IMP in15%alfalfa meal group wassignificantly lower than control (P<0.05) and in this group the GMP content was alsosignificantly lower while other groups had no significant difference. All the othergroups could significantly improve the EUC content in liver(P<0.05) except15%alfalfameal group(P>0.05).0.55%haematococcus pluvialis group could significantly improvethe EUC content in muscle (P<0.05)while the other groups had no significant differencewith control.(4) No significant difference in weight gain was found bentween spirulina,15%alfalfa meal groups and control group. The additions of2%Spirulina,3%Spirulina and15%Alfalfa meal in feed have no significant effect on crabgrowth(P>0.05), and the additions of0.35%Haematococcus pluvialis,0.55%Haematococcus pluvialis and10%Alfalfa meal in feed all can improve the crab averageweight gain rate significantly(P<0.05). All groups have no significant effect on GPT andGOT of liver and serum of the crab (P>0.05). The groups that add Spirulina in feedrespectively have no significant effect on total antioxidant capacity of serum (P>0.05).The groups that add Haematococcus pluvialis and Alfalfa meal in feed respectively canimprove the serum total antioxidant capacity of the crab significantly (P<0.05). Thegroups that add Spirulina, Alfalfa meal and Haematococcus pluvialis in feedrespectively have no significantly effect on composition of crab body (P>0.05). Theseresults suggest that: these two kinds of microscopic algae and alfalfa meal can improvethe organoleptic properties of crab at all addition in this study, and2%spirulina,0.35%haematococcus pluvialis,10%alfalfa were the suitable additive amount.3. The adult crabs usually hold food to eat, so they can’t eat the microscopic algaedirectly, so snail may play a role of bridge in improving the crabs’ body color and flavor.For this reason, according to the food chain in the lake ecosystem, we select theSpirulina and the Haematococcus pluvialis to feed5kg snail, with the amount of12gand10g respectively per day by uniformly mixing them in the water, The purpose of theexperiment is to study the regulation of accumulation of these two microscopic algae inthe snai body, to further explain the ecological mechanism of the difference between the lake crab and the pond crab. The results showed that: We can intensify the snail byfeeding the microscopic algae and feeding with the nail is expected to enhance the bodycolor of the crab. |
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