| Flavor is one of the most important factors to evaluate the quality of food.The yield of freshwater fish in China is rich,which is characterized by high water content,high protein and low fat,so it is extremely easy to spoil.In addition,it mainly lives in the fresh water environment,with fishy and muddy taste,resulting in low processing rate.In this study,grass carp was taken as the research object to investigate the effects on flavor components in the processing of Shanghai smoked fish.High performance liquid chromatography(HPLC),amino acid auto-analyzer and solid phase microextraction-gas chromatography-mass spectrometry(SPME-GC-MS),electronic tongue and electronic nose were employed to extract,analyze and identify flavor components.Moreover,the characteristics of flavor components of cultured grass carp and tilapia meat,as well as the effects of seasonings and different processing stages on the flavor were investigated.The effects of fresh grass carp,different pickling methods in first pickling process,frying process after different pickling methods,and second pickling on taste components were studied.Results showed that the fresh grass carp,pickling with cooking wine,pickling with cooking wine and salt,pickling with cooking wine and onion,pickling with cooking wine and ginger,pickling with cooking wine and garlic,pickling with cooking wine and pepper,pickling with cooking wine and soy sauce as well as pickling with all seasonings samples were detected respectively 215.91,156.59,180.05,164.91,175.84,200.32,199.48,275.57 and 270.20 mg/100 g Inosine monophosphate(IMP).Among them,the content of pickling with cooking wine was the lowest and that of pickling with cooking wine and soy sauce was the highest.IMP was the main umami nucleotide.The flavor amino acids accounted for 28.33,30.64,33.76,32.48,33.08,29.80,37.01,39.98 and 38.66% of the free amino acids,respectively.Glutamic acid was the main umami amino acid of first pickling.The IMP content of frying was 78.28,129.38,109.10,129.93,104.90,87.47,61.55,22.61 and 36.98% higher than that first pickling,respectively.The TAV of IMP of frying sample was greater than that of first pickling sample,and IMP also was the main umami nucleotide in the processing of frying.The IMP content of second pickling with oil and water was the lowest and that of Shanghai smoked fish was the highest in the processing of second pickling.The TAV in each sample was greater than 10,so IMP was the main umami nucleotide at different processing stages.Hypoxanthine(Hx)was bitter,and its content in Shanghai smoked fish was 2.16 times lower than that of fresh fish.The contents of flavor amino acids of frying were 15.39,23.63,21.48,20.91,14.18,44.03,14.27,15.51 and 16.14% higher than that first pickling,respectively.The glutamic acid and glycine were the main umami amino acids in the processing of frying.The contents of aspartic acid and glutamic acid in Shanghai smoked fish increased by 7.61 and 105.66 mg/g,compared with that of fresh grass carp,respectively.The aspartic acid and glutamic acids were the main umami amino acids in the processing of second pickling.The taste of grass carp meat of different processing stages could be well distinguished by electronic tongue.After the first pickling,frying and the second pickling,the freshness of fish was improved significantly.The effects of fresh grass carp,different pickling methods in first pickling process,frying process after different pickling methods,and second pickling on volatile components were studied.The results showed that volatile components of fresh grass carp and each sample of first pickling were detected 36,40,45,36,53,55,41,45 and 75 kinds.Hexanal,(E)-2-octenal,nonanal,decanal,(E,E)-2,4-decadienal,1-octen-3-ol,caryophyllene,2-methylbutyric acid methyl ester and 2-pentyl furan had important contributions to the overall flavor formation.The volatile components of each sample in the processing of frying were detected 34,41,44,46,45,44,57,54,and 73 kings,respectively.2-methyl butanal,hexanal,nonanal,decanal,2,4-decadienal,(E,E)-2,4-decadienal,1-octen-3-ol,3-ethyl-2,5-dimethyl pyrazine and 2-methylbutyric acid methyl ester were main flavor active components in the processing of frying.The volatile components of second pickling with oil and water,second pickling with oil,water and sugar,second pickling with oil,water,sugar and soy sauce and Shanghai smoked fish were detected 66,59,70 and 78 kinds,respectively.3-methyl butanal,2-methyl butanal,hexanal,heptanal,benzeneacetaldehyde,(E)-2-octenal,nonanal,decanal,(E,E)-2,4-decadienal,1-octen-3-ol,D-limonene,3-ethyl-2,5-dimethyl pyrazine,2-ethyl-3,5-dimethyl pyrazine,2-methylbutyric acid methyl ester and 2-pentyl furan were key flavor compounds of Shanghai smoked fish,mainly composed of aldehydes,alcohols,hydrocarbons,pyrazines,esters and furan and contributed a lot of flavor.The volatile components of tilapia of Shanghai smoked fish in five processing stages(fresh tilapia,first pickling,frying,first pickling followed by frying and Shanghai smoked fish products(first pickling followed by frying and then second pickling))were employed to analyze and identify.The results showed that IMP,as main umami nucleotide,its contents of latter stages were significantly higher than that of the former.Moreover,the contents of free amino acids and taste amino acids had the same trend to the IMP,among them,aspartic acid and glutamic acid had the greatest influence on the flavor of Shanghai smoked fish.In addition,a total of 50,84,65,78 and 82 volatile components were respectively detected in fresh tilapia,first pickling,frying,first pickling followed by frying and Shanghai smoked fish products,which were mainly composed of aldehydes,ketones,alcohols and hydrocarbons.Therefore,the fishy smell of tilapia was greatly improved by pickling and frying because they were the main reason of its flavor formation.In the processing of Shanghai smoked fish,the seasonings(cooking wine,onions,ginger,garlic,pepper and soy sauce,etc.)used in first pickling,frying and maillard reaction occurred in second pickling had an important contribution to improving the fishy and enhancing the flavor,and were also the main reason for the formation of flavor. |
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