Study On Preparation And Umami Mechanism Of Taste Peptides From Chicken Liver And Fish Bone Paste

Meat by-products are all parts except meat in the process of animal slaughtering and processing,including viscera,bones,skins,blood,etc.Protein,minerals,and other nutrients were abundant in meat by-products.At the moment,meat by-product production was high,but utilization was poor.The primary reasons were that the processing objectives of meat by-products were unclear,processing technology was not ideal,the industrial scale of factory production was modest,and production efficiency needs to be improved.To improve the utilization rate of meat resources and lower production costs,chicken liver and fish bone paste with different water contents were selected as raw materials.Peptides with nutritional value and flavor were produced by hydrolyzing chicken liver and fish bone paste with protease.The taste characteristics of peptides were detected by the electronic nose,gas chromatography-mass spectrometry,electronic tongue,liquid chromatography,and sensory evaluation.The amino acid sequence of taste peptides was obtained by mass spectrometric detection,and the flavor and activity of taste peptides were predicted by the peptides database.The umami mechanism of peptides was explored by molecular docking.This study was beneficial to the mining and screening of flavor peptides.The peptides prepared in this project had obvious umami and saltiness characteristics and can be used as a flavor and nutritional supplement to be added to human or pet food.Therefore,the developed technology had a wide application prospect.The main contents and results of this paper were as follows:（1）The enzymolysis conditions of chicken liver and fish bone paste were optimized.Chicken liver and bonito bone paste were mixed in equal mass,and the enzymatic hydrolysis reaction was carried out at a high substrate concentration.The hydrolysis degree,polypeptide conversion rate,and sensory evaluation score of the enzymatic hydrolysate were used as indicators to optimize the enzymatic hydrolysis reaction conditions.The optimal enzymatic hydrolysis conditions were obtained as follows:the mass ratio of papain（P）to bromelain（B）was 1:1,the addition of protease was 7000 U per gram of protein,and the material-liquid ratio was 9:1.Under these conditions,the degree of hydrolysis of enzymatic hydrolysate was 26.74%,the polypeptide conversion rate was 63%.The peptides obtained by enzymolysis had umami taste,salty taste,and burnt aroma.The hydroxyl radical scavenging rate of enzymatic hydrolysate was 21.4 times that of the raw material.The DPPH radical scavenging rate of enzymatic hydrolysate was 64.1 times that of the raw material.The ABTS radical scavenging rate of enzymatic hydrolysate was 66.1 times that of the raw material.The IC₅₀ for the scavenging of hydroxyl radical,DPPH radical,and ABTS radical was 4.16 mg/m L,0.15 mg/m L,and 0.13 mg/m L,respectively.（2）The flavor characteristics of peptides made by the chicken liver and fish bone paste were studied.Homogenize and filter the enzymatic hydrolysate,and freeze-dry the filtrate to obtain peptide powder.Detect the types and components of volatile substances of peptides by the electronic nose and gas mass spectrometer.The taste characteristics,taste threshold,and synergy with sodium glutamate were described by electronic tongue detection value,free amino acid content,taste nucleotide content,and sensory evaluation test.The results showed that:（1）The main aroma components of the flavored peptide were octanal,styrene,and butyric acid,which had aromatic odors,and styrene was the characteristic flavor substance of peptides.（2）The main taste characteristics of peptides were umami,salty,and bitter.（3）The taste activity values（TAV）of glutamic acid（E）and aspartic acid（D）in the free amino acids of taste peptide were 513.60 and 469.00 respectively,which were much higher than other amino acids.The content of guanine nucleotide（GMP）in free nucleotides was the highest,with the highest taste activity value of 3.43.The main taste feature of free amino acids and nucleotides was umami,and the EUC of the taste peptide was 364.75 g MSG/100 g.（4）The taste threshold of umami and salty taste of the savory peptide was 0.25 mg/m L,and the sweetness threshold was 0.125 mg/ml;（5）Sodium glutamate（MSG）had a synergy on the taste presentation of peptides.（3）The relationship between biological activity and flavor characteristics and amino acid composition of representative peptides screened from taste peptides obtained by the chicken liver and fish bone paste was studied.The De novo sequencing method was used to detect the taste peptides by mass spectrometry,and five representative peptides were screened out.The biological activity and flavor characteristics of representative peptides were predicted by Innovagen,Toxin Pred,and BIOPEP-UWM databases.The results were as follows:（1）Five representative taste peptides were GVIHFQQQGSGPVK,LPEDLIK,GFFDRGASIVE,QPLDDDFVR,and VDVLEDKLK,which were screened out from the mass spectrometry results by the content and reliability;（2）It was found that amino acids such as G,P,V,K,E,and L in five representative peptides make the peptides had potential biological activities,and amino acids such as D,E,K,and P make the peptides had good taste characteristics such as umami,salty and sweet,and amino acids such as F,V,and L had potential bitter characteristics.（4）The umami mechanism of representative taste peptides obtained from chicken liver and fish bone paste was studied.Using Chem Draw and Chem3D software to draw the 2D and 3D structures of five representative taste peptides.Using T1R2a-T1R3 as a template（PDB ID:5X2P）,the structure of the T1R1-T1R3 receptor was obtained by homologous modeling.Five representative taste peptides were docked with the T1R1-T1R3 receptor.The results were as follows:（1）The interaction between peptides and T1R1-T1R3 receptor were hydrogen bond and electrostatic interaction,（2）Aspartic acid（Asp）and glutamic acid（Glu）were the main binding sites in T1R1-T1R3 receptor.（3）In the docking of five peptides with the T1R1-T1R3 receptor,the alkaline amino acid and hydrophilic amino acids in the peptides were the main sites of docking,such as lysine（K）,glycine（G）,and aspartic acid（D）.The docking score of peptide GVIHFQQQGSGPVK with T1R1-T1R3 receptor was the highest.,and the docking force between peptide VDVLEDKLK and T1R1-T1R3 receptor was the most.（4）The docking results of"peptide+sodium glutamate"with T1R1-T1R3 receptor showed that the main sites in peptides were arginine（R）,lysine（K）,and glycine（G）.The docking score of"GFFDRGASIVE+MSG"with the T1R1-T1R3 receptor was the highest,and the docking force between"QPLDDDFVR+MSG"and T1R1-T1R3 receptor was the most.（5）Compared with the docking of a single peptide with the T1R1-T1R3 receptor,the addition of sodium glutamate changed the site of conjugation,the type and quantity of force between peptide and T1R1-T1R3 receptor,and the influence of sodium glutamate was related to the structure of peptides and has specificity.In this study,the synergy of sodium glutamate and taste peptide was to increase the stability of the binding of peptides with a high proportion of flavor amino acids to T1R1-T1R3 receptor and decrease the stability of the binding of peptides with a high proportion of bitter amino acids to T1R1-T1R3 receptor.