| Surimi products are the traditional aquatic food that originated in China and are widely favored by consumers around the world.With the increase of the production of surimi products in China,the demand for frozen surimi in the surimi product industry has increased rapidly.However,due to the limited resources of seawater fish which are suitable for frozen surimi processing in China,freshwater fish such as silver carp and grass carp have become key raw materials for frozen surimi.Flavor,nutrition,texture,and safety are four important indicators to evaluate the quality of surimi products.At present,most of the studies on the surimi products focused on surimi protein properties,gelation mechanisms,influencing factors,quality evaluation,and safety control.Surimi products from different sorts(freshwater fish and seawater fish)have distinct flavor qualities,and even the flavor characteristics of surimi products from the same type but the different species also have certain differences.However,the composition of key flavor substances that lead to the different flavor characteristics of surimi products from various types and varieties are not clear,and the ways for distinguishing and identifying different varieties of surimi products are still unknown.Therefore,three kinds of seawater surimi,including largehead hairtail(Trichiurus lepturus,LH),red sea snapper(Pagrosomus major,RSS),and golden thread(Nemipterus virgatus,NV),and three kinds of freshwater surimi,including silver carp(Hypophthalmichthys molitrix,SC),grass carp(Ctenopharyngodon idella,GC),and black carp(Mylopharyngodon piceus,BC),were used as materials in this study.Surimi products were prepared by a two-stage thermal process.The characteristic taste compounds and inter-species differences in surimi and its products were identified by taste analyzers,high performance liquid chromatographu(HPLC),ultra performance liquid chromatographs(UPLC),gas chromatography-mass spectrometers(GC-MS),and other scientific techniques were combined with taste activity value(TAV).The characteristic odor substances of surimi and its products were determined by odor analyzer,gas chromatography-ion mobility spectrometry(GC-IMS),direct solvent extraction-solventassisted flavor evaporation(SAFE),gas chromatography-mass spectrometry/olfactometry(GC-MS/O)combined with aroma extraction dilution analysis,and odor activity value(OAV).Furthermore,the differences in flavor characteristics of freshwater and seawater surimi,as well as its products,were characterized by the multivariate statistical method,and the flavor fingerprints of surimi and its products were established.The present study can lay a foundation for the evaluation and regulation of flavor quality of surimi products.The main research results are as follows:1.Identification of the taste profile and characteristic taste substances of surimi and its productsThe taste characteristics of six types of surimi and surimi products were studied using electronic tongue,HPLC,UPLC,GC-MS,and other technical techniques,and their characteristic taste compounds were separated and identified.The taste profiles of surimi and surimi products from different types and varieties differed significantly.The content of umami and sweet amino acids,guanosine monophosphate(GMP),inosinic acid(IMP),and betaine in LH surimi were the highest,which were 2.09 mg/100 g,15.15 mg/100 g,0.78μmol/g,0.36 μmol/g,and 0.73 mg/g,respectively.BC surimi had the lowest levels of umami,sweet,and bitter amino acids,with 0.87 mg/100 g,3.32 mg/100 g,and 9.65 mg/100 g,respectively.The content of bitter amino acid and bitter Hx in GC surimi were the most,which were 35.66 μmol/g and 1.48 μmol/g,respectively.The ratio of saturated fatty acids and monounsaturated fatty acids of freshwater surimi and its products were significantly higher than those of seawater surimi and its products(P<0.05),while the proportion of polyunsaturated fatty acids was significantly lower than that of seawater surimi and its products(P < 0.05).TAVs results showed that the key taste substances in the six surimi were: Histidine(His),Phenylalanine(Phe)and GMP in SC surimi and GC surimi;GMP in BC surimi;Glutamate(Glu),Phe and GMP in LH surimi;Phe and GMP in RSS surimi;Alanine(Ala),Phe and GMP in NV surimi.The contribution rate of free amino acids and flavor nucleotides to the taste of surimi and surimi products decreased after the heat treatment.The key taste substance in the six surimi products was GMP in surimi products from LH and NV.2.Identification of odor profile and characteristic odor compounds in surimi and its productsThe odor characteristics of six surimi and surimi products were determined by electronic nose,GC-IMS,SAFE-GC-MS/O,and other technical means,and their characteristic odor compounds were separated and identified.The results showed that the odor profiles of freshwater surimi and its products were significantly different from those of seawater surimi and its products,and the odor profiles of surimi and its products of the same type and different species were similar to a certain extent.The results of GC-MS/O and OAVs showed that the composition and content of odor compounds in different types and varieties of surimi and their products were significantly different.The characteristic odor substances of freshwater surimi and its products were hexanal,heptanal,octanal,(E)-2-hexenal,(E)-2-nonenal with a grassy smell,(Z)-4-heptenal,(E,E)-2,4-heptadienal,(E,Z)-2,4-decadienal with a fishy smell and an oil odor,(E,E,Z)-2,4,6-nonatrienal with a fresh fishy odor,(E)-4,5-epoxy-(E)-2-decenal with a metallic odor,and 1-octene-3-one and 1-octen-3-ol with a mushroom odor;Bromine-containing compounds such as dibromochloromethane,tribromomethane,2-bromo-5-methoxytoluene,which had a fishy and sea-breeze odor,as well as some unidentified odorants with a sea odor,were the characteristic odor substances of seawater surimi and its products.3.Establishment of the flavor fingerprints of surimi and surimi productsOn the basis of analyzing and clarifying the flavor compounds in different types and species of surimi and their products,significance analysis of microarray(SAM),partial least squares discrimination analysis(PLS-DA),cluster analysis,and heatmap were used to establish the flavor(taste and smell)fingerprints of surimi and its products.SAM was applied to screen out 49 and 45 different taste substances in surimi and surimi products,respectively,and 87 and 92 different odor substances in surimi and surimi products,respectively.The flavor(taste and odor)fingerprints of surimi and its products were established according to the different taste and odor substances.The flavor fingerprints showed that the flavor characteristics of freshwater surimi and its products significantly differed from those of seawater surimi and its products.Moreover,the flavor characteristics of different varieties of freshwater surimi and its products or seawater surimi and its products were similar to some extent,but they can also be distinguished by the fingerprints.Furthermore,PLS-DA was utilized to differentiate the taste and odor characteristics of the six kinds of surimi and surimi products.Seventeen various types of key different taste substances,such as adenosine triphosphate,and 20 different types of key different taste substances,such as glycine,were chosen as taste fingerprints to distinguish the taste characteristics of six distinct types of surimi and its products.Also,to differentiate the odor characteristics of six kinds of surimi and its products,29 kinds of key differential odor compounds such as nonanal and 29 kinds of key distinct odor substances such as octanal were screened out as odor fingerprints. |
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