Flavor Properties And Mechanism Of Umami Peptides Extracted From Tilapia Mandibles

Tilapia(Oreochromis niloticus)is a common freshwater farmed fish in our country and a large amount of scraps are produced during processing and production,which caused great environmental pollution and the waste of resources.These scraps contain more flavor substances,rich in nutrients and have a good taste.Among them,tilapia lower jaws are rich in protein,which can be used as a good source of umami peptide research.In this study,tilapia lower jaw was used as the research object to analyze its nutrients and flavor substances.The hot water extraction method was used to prepare the tilapia lower jaw aqueous extract(TJAE),and investigating the influence of different taste substances on the umami taste of the aqueous extract.Ultrafiltration and gel filtration chromatography are used for the separation and purification of umami peptides.Sensory evaluation was used to screen the high intensity components of umami taste.Ultra Performance Liquid Chromatography-Quadrupole-Orbitrap-mass spectrometry/mass spectrometry(UPLC-Q-Orbitrap-MS/MS)was use to identify umami peptides.The amino acid sequence of the umami peptides were synthesized by the liquid phase synthesis method,and the sensory analysis combined with the electronic tongue was used to verify and analyze the taste characteristics of the synthesized peptide.Homology modeling was used to construct the 3D structure of the umami taste receptor T1R1/T1R3 and molecular docking was used to study the interaction between umami peptides(ligands)and umami taste receptors T1R1/T1R3 to reveal the umami mechanism.The main findings are as follows:1.The nutrient composition and taste substances of the tilapia lower jaw were analyzed.The results showed that the protein content in the tilapia lower jaw was as high as 51.68%,and the fat and ash content were 32.84% and 0.43%,respectively.The content of free amino acids is rich,including eight essential amino acids for the human body,which can meet the daily needs of the human body.Among them,the content of taste amino acids was 32.12 mg/100 g,accounting for 80.12% of the total free amino acids.The content of the umami amino acids aspartic acid(Asp)and glutamic acid(Glu)is 5.07%.The content of unsaturated fatty acids in free fatty acids is 15.95%,with the highest content of C18:1(oleic acid),which is the essential fatty acid for the human body.Polyunsaturated fatty acids contain C22:6(DHA),which is vital to the human body,with a content of 1.04 %.In addition,tilapia lower jaw is rich in flavor substances.In addition,there are many kinds of taste substances from the tilapia lower jaw,and succinic acid and nucleotides play an important role in taste.These special taste substances give tilapia a rich mouthfeel and delicious taste.2.The hot water extraction method was used to prepare the tilapia lower iaw aqueous extract.The tilapia lower jaw aqueous extract was ultra-filtered to obtain the high umami intensity fraction with MW<3 k Da,which was further separated by gel chromatography to obtain the strong umami fraction F4.UPLC-Q-Orbitrap-MS/MS was used to identify the peptide sequence of the high intensity component F4.Five peptides of VADLMR,STELFK,DALKKK,FVGLQER,and VVLNPVARVE were successfully screened from F4.The bioactive peptide database was used to predict the sensory activity,and the result found the five peptides have a strong umami taste.3.In order to further verify the taste characteristics and taste mechanism of the identified peptides,a liquid phase synthesis method was used to synthesize small molecule peptides,and sensory analysis combined with electronic tongue was used to evaluate and analyze the taste characteristics of the synthesized peptides.The results showed that the five synthetic peptides all had umami taste,and they were verified as umami-taste peptides with a freshness threshold of 0.125~0.250 mg/m L,which has a stronger umami taste threshold(0.3 mg/m L)than MSG.The taste mechanism of umami peptides is further studied by homology modeling and molecular docking technology.SWISS-MODEL was used to construct a three-dimensional model of umami taste receptor T1R1/T1R3,and SYBYL software was used to the molecular docking of umami peptides and umami taste receptor T1R1/T1R3.The result showed that the five umami taste peptides all bind to the umami taste receptor T1R1/T1R3 by intercalating into the "Venus flytrap domain (VFTD)" of the T1R3 subunit.The main forces for the combination of the peptides and taste receptor are hydrogen bonding and hydrophobic interaction.The key amino acid residues of umami peptides binding to umami taste receptors T1R1/T1R3 are Asp219,Glu217 and Glu148.