Analysis Of Flavor Of Fish Sauce And T He Purification And Identification Of Its Small Peptides

Fish sauce is a kind of liquid seasoning with unique flavor and rich inamino acids and flavor peptides.The protein,fat and other ingredients in low-valued marine fishes were fermented through the use of salt-tolerant and halophilic microorganisms,or by many kinds of other proteases and enzymesthatthey contain under condition of high salt concentrationfor several months or even years.It is very important to study the characteristic volatile flavor substances,amino acids and water-soluble small peptides of fish sauce,in orderto reveal the flavor compositions of fish sauce and realize the standardization of production process.Good flavor of low salt fish sauce withlow salinityobtained through the desalination treatment of traditional fish sauce fermentation broth,is the future developmentdirection ofthe production of fish sauce.The research content and results of this paper are as follows:1.The composition of the volatile flavor compounds in 11 kinds of commercially available fish sauce was analyzed by headspace solid-phase microextraction and gas chromatography-mass spectrometry.Among them,the contents of butyric acid,acetic acid,4-methylpentanoic acid,propionic acid,1-penten-3-ol,2-methylbutanal and 3-methylbutanal,benzaldehyde,2-pentanone,?-caprolactone,methyl mercaptan,Methyl sulfide,dimethyl disulfide and dimethyltrisulfide,2-ethyl-furan,2-pentylfuran and phenol is high,which were the main active compositions related to flavor.2.The contents of 18 amino acids in fish sauce were determined by automatic amino acid analyzer.The main amino acids include glutamic acid,lysine,leucine,Aspartic acid,alanine,glycine,isoleucine and valine.The relative content of glutamic acid,which is closely related to the flavor of fish sauce,is among 17.27 ~ 41.24% in 11 kinds of fish sauces,and it can be used as a characteristic amino acid of fish sauce.Most of the essential amino acids in fish sauce accounted for 37% to 55% of the total amino acids.The sum of the relative percentages of fresh and sweet amino acids is higher than that of bitter amino acids.Taurine is a characteristic functional amino acid in fish sauce,which is about 200.00 mg / 100 mL in the third fish sauce andbelow 60.00 mg / 100 mL in tertiary fish sauce.3.29 small peptides including 18 dipeptides and 11 tripeptides were purified and identified by ultrafiltration,electrodialysis and HPLC-Q-TOF-MS from Shantou fish sauce through traditional fermentation for 1.5 years.Different taste characteristics of the small peptides were related to the type and sequence of their amino acid residues.Among them,23 peptides were screened and thensynthesized by solid phase synthesis including dipeptides and tripeptides with Pro residues such as Ile-Pro?Val-Pro?Tyr-Pro?Lys-Pro?Gly-Pro?Ala-Pro?Asp-Pro?Ser-Pro??-Asp-Lys-Pro?Pro-Ala-Pro?Pro-Gly-Pro?Val-Pro-Leu and dipeptides and tripeptides with gamma-glutamate residuessuch as?-Glu-Ile,?-Glu-Met,?-Glu-Val-Gly,?-Glu-Leu-Gly and ?-Asp-Leu,Gly-Ala-Ser-Val,?-Asp-Hyp,Leu-Hyp,Val-Hyp.4.Electrodialysis(ED)technique was utilized to desalinate the traditional fish sauce.The results showed that under the condition of voltage of 9 V and flow rate of 4 cm/s,the contents of amino nitrogen,amino acids and volatile aroma compounds in the fish sauce at the target salt content of 22%,20%,15%,10%,5% and 2%(w/w)decreased nonlinearly with the increasing of desalination.When the salt content was reduced to 20%,the loss rate of ammonia nitrogen reached to relatively low 8%.When the salt content reduced to 2%,the loss rate of several bitter amino acids such as tyrosine,arginine,histidine and lysine in free amino acids decreased to 51.60%,49.41%,42.41% and 31.12%,respectively.K inds of flavor compounds did not change.Except that the content of 2-methyl butyraldehyde,3-methyl butyraldehyde and benzaldehyde increased,the relative percentages of acids,ketones,nitrogen compounds and sulfur-containing compounds decreased as the increase of desalination extent,but still higher than their taste threshold.The results of sensory evaluation showed that with the salt content was reduced to 20%,the desalination of electrodialysis had almost no effect on the whole flavor of fish sauce,which was beneficial to the preservation of fish sauce,and could provide guidance for the production of low salt fish sauce.