| China is the largest shellfish producing country in the world,and the shellfish industry was an important part of fishery industry.However,due to the shellfish products cannot fulfill the sanitation requirements of many developed country,such as Europe,America and Japan,therefore the shellfish products of China only take a small share of the external market.Therefore,safety and hygienic problem of shellfish farming and processing have become the major obstacle to the development of shellfish industry.Purification,as an important means to solve this problem,can effectively eliminate the bacteria and pollutants,improve the quality of products,and help China open the international market of shellfish products and improve the competitiveness of products.In this study,the representative cultured shellfish-hard shell clam was taken as the research object and the biological purification method that microalgae purification was applied.Through the multivariate statistical analysis of volatile components changes as well as elimination effect foodborne bacterium,the feasibility and superiority of microalgae depuration for shellfish were systematically evaluated.Furthermore,this investigation could also provide basic data and scientific basis for technologic upgrading and industrial improvement.In this research,dynamic changes of volatile compounds constitution were firstly analyzed,and found that traditional shellfish depuration not only resulted in loss of aroma components but also led sensory quality decreasing.Then,the positive effect of microalgae on shellfish sensory quality enhancement applied in shellfish depuration,were presented by the comparison between volatile profile of microalgae depuration(Isochrysis galbana)and traditional depuration(seawater).Finally,in order to select the best one from three alternative microalgae species(Isochrysis galbana,Thalassionsira pseudonana,Platymonas helgolandica)which were planned to apply in shellfish depuration,sensory quality and aerobic bacterial count were selected as two major indexes for the evaluation of depuration effect.The results showed that volatile components of hard clam declined continuously during the sea water depuration procedure,and loss of aldehydes and furans was the most serious.Aldehydes are the important source of characteristic aroma(fresh,vegetable odor)of marine products for its low sensory threshold and high concentration,and furan have typical meaty,fatty,butter aroma and closely related with shellfish taste.Therefore,deterioration of clam flavor is commonly caused by depuration treatment.However,after microalgae depuration,concentration of most aroma compounds increased especially some sulfur compounds which were detected which added marine odor to products.Therefore,microalgae can fortify aroma and improve hard clam' sensory quality.From the perspective of microbial clearance result,microalgae depuration had better performance than traditional seawater depuration with statistic difference(p<0.05).The results indicated that Isochrysis sphaerica and Thalassiosira pseudonana did better in both sensory quality enhancement and bacteria clearance compared with Platymonas helgolandica.In hard clams' muscle tissue,the evident increase of esters and unsaturated alcohols enhance fresh and vegetable-like odor,In hard clams' visceral mass,the elimination of bacteria and 4off-odor compositions which are mainly accumulated from aquaculture water declined to varying degrees These 4 compounds included 2-methylisobornyl(earthy odor),trimethylamine(fishy odor),triethylamine(amine odor),and ethyl mercaptan(garlic-like odor).Through the above analysis and discussion,microalgae depuration is more efficient and effective compared with traditional seawater depuration,furthermore Isochrysis galbana and Thalassionsira pseudonana are recommended for shellfish depuration. |
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