Rapid Identification Of COD Products And Study On Their Lipids And Flavor Sudstances

This paper is composed of three parts.The first,TLC-ImageJ method was established for the qualitative and quantitative of different lipids components from common cod products,and the rapid identification method for cod products was further established.The second,fatty acids from different cod products were analyzed by gas chromatography.The third,headspace solid phase microextraction and gas chromatography-mass spectrometry were used to study the volatile substances of cod products under different processing.Firstly,TLC-ImageJ method was established for the qualitative and quantitative of different lipids components from common cod products,and based on this method,a rapid identification method was established for cod products.The results of TLC images were analyzed by ImageJ under the condition that the span was 6cm and the developing agent ratio was n-hexane : ether : acetic acid = 80:20:2(V: V: V).The polar,neutral and non-polar lipids in each sample were well separated,and the Rf values of phosolipid,triglyceride and wax ester were 0.01,0.67 and 0.96,respcetively.The spot’s OD values of phospholipid,triglyceride and wax ester had a good linear relationship with their concentrations(﹥0.99)under their concentration range(1-160 mg/mL).The phospholipid only exists in the lipids of Gadus morhua and Gadus macrocephalus,and their contents are 67.79±1.04 % and 68.83 ± 1.77 % respectively.Triglyceride was only significantly present in the lipids of Anoplopoma fimbria and Dissostichus eleginoides,with the content of 69.31 ± 0.85 % and 67.34 ± 1.24 %,respectively.As to wax ester,it was only present in the lipids of Ruvettus pretiosus,with the content up to 90.95 ± 1.73 % of the total lipids.The limit of quantification was 1mg/mL and a relative standard deviation of 0.1 %—4.8 % with good stability,and the cod products can be distinguished by the method of TLCImageJ in less than 12 minutes.Compared with PCR,DNA barcoding,TLC-FID and other technologies,this method has the advantages of on-line,rapid analysis and no need of special instruments.Secondly,five common cod products from the market were analyzed by gas chromatography,and their lipid nutritional value was further evaluated.The result showed that there are 13,11,13,13 and 6 kinds of fatty acids in Gadus morhua,Gadus macrocephalus,Anoplopoma fimbria,Dissostichus eleginoides and Ruvettus pretiosus respectively.The Gadus macrocephalus doesn’t contain C 17: 0 and C17: 1.Except for C 17: 0 and C17: 1,Gadus macrocephalus’ s composition and content of fatty acid are similar to that Gadus morhua.The fatty acid composition of the Anoplopoma fimbria was the same as that of Dissostichus eleginoides,and the content of each component was similar,compared with the Gadus morhua and Gadus macrocephalus,they lacked C20:1n9 and C20:4n6.Ruvettus pretiosus,which is often used to pretend to be the above four kinds of fish,only contains six kinds of fatty acids.It is quite different from the others.The most important fatty acid in it is oleic acid,and the relative content of oleic acid is as high as 80.29 %-84.76 %.The AI and TI indexes of Gadus morhua,Gadus macrocephalus,Anoplopoma fimbria,Dissostichus eleginoides were all in the range of 0.26-0.61.There were no omega-3 fatty acid in Ruvettus pretiosus,which had no exponential significance.The results of systematic clustering and fatty acid index analysis of five kinds of fish fatty acids showed that the fatty acid profile of Gadus morhua and Gadus macrocephalus were similar and the lipid nutritional value was similar,while the fatty acid profile of Anoplopoma fimbria and Dissostichus eleginoides were similar and the lipid nutritional value was similar,which were obviously different from that of Ruvettus pretiosus.The five species of fish can be classified through the analysis of heat map in the case that the overall outline of fatty acids is similar.Finally,HS-SPME-GC-MS was used to analyze the volatile components of cod products by two processing methods,frying and steaming.It was found that the volatile components of the cod products with frying and steaming processing contained aldehydes,ketones,alcohols,benzene series,esters,acids,hydrocarbons,ethers,N-containing compounds and S-containing compounds,a total of 10 kind of compounds.Among them,aldehydes,ketones,alcohols and benzene series were the main contributions to the flavor of the samples.After PCA analysis,it was found that using two cooking methods,except for the similar overall contour of volatile components between Anoplopoma fimbria and Ruvettus pretiosus,the other samples were easily differentiated.By describing the flavor characteristics of each sample by two cooking methods,it is found that the flavor characteristics of Gadus morhua,Gadus macrocephalus,Anoplopoma fimbria and Dissostichus eleginoides mainly include fruit-sweet flavor and cream-milk flavor,while the main flavor of Ruvettus pretiosus is only fruit-sweet flavor and a little fishy odor.Therefore,for the processed cod products,only from the flavor characteristics of Ruvettus pretiosus and the other four cod products can be found the difference.In terms of flavor characteristics of processed cod products,mackerel showed significant differences from the other four cod products.In the flavor analysis,the Gadus morhua and Gadus macrocephalus with the same species had great difference in flavor characteristics by different cooking,while the other three species had little difference.