Effects Of Amino Acids And Oligopeptides On The Umami Of Soldier Crab Sauce

Soldier crab sauce is a kind of aquatic fermented seasoning which is peculiar to Beihai,Guangxi.In this paper,crab sauce was used as raw material to study the umami components,emphasized on the separation,purification and identification of naturally occurring oligopeptide in crab sauce,and studied the amino acid sequence.Firstly,the basic indexes such as crude protein,crude fat,salt content,peptide content and ash of crab sauce were determined and analyzed,and their nutritional value was determined.Then,ultrafiltration,ethanol extraction,gel column chromatography,anion exchange adsorption technology,sensory evaluation and e-Tongue taste analysis method were used to separate and purify oligopeptide from crab sauce,and their amino acid composition and taste characteristics were analyzed.The amino acid sequence of the oligopeptide was determined by mass spectrometry/mass spectrometry.The secondary structure was determined by circular dichroism.The specific research results were as follows.The basic nutrients of crab sauce were studied.The crude protein content was 3.95%,the polypeptide content was 2.95%,the crude fat content was 0.10%,the salt content was 13.18%,and the ash content was 22.99%.It was nutritious aquatic fermented seasoning which had higher protein content and lower fat content.Crab sauce was rich in flavor and it was also a high-quality raw material for preparing umami peptides.UF-1(10 kDa retentate),UF-2(3 kDa retentate)and UF-3(<3 kDa)were obtained by sequentially removing the crab sauce with ultrafiltration membranes for molecular weights of 10 kDa and 3 kDa.The three components of permeate were subjected to sensory evaluation and e-Tongue taste analysis,and the UF-3 component with the strongest umami taste was selected for gel column chromatography and linear elution to obtain three components GF-1 and GF-2 and GF-3.By sensory evaluation and amino acid analysis and e-Tongue taste analysis,it showed that GF-3 containing 39.38%umami amino acid were the main umami component.Then its component were identifyed by analytical RP-HPLC and results showed that the compounds in the GF-3 component were similar in polarity,less in impurities,and could be used in the next structural analysis.The food-grade ethanol solution was used to separate the crab sauce,and the odor value of the umami taste was optimized to optimize the concentration of ethanol.At the concentration of 50%of the ethanol solution,the alcoholic component had the best umami taste.The components were extracted by anion exchange adsorption resin.The components were analyzed by amino acid analysis,sensory evaluation and e-Tongue taste analysis before and after adsorption.The analysis results showed that the component IE-3 adsorbed by the anion resin had the best umami taste and contained 56.38%umami amino acid.It could be used for the next structural analysis.The two oligopeptide sequences,LF(Leu-Phe,279.1713 Da)and TTD(Thr-Thr-Asp,336.2211 Da),which were extracted with gel column chromatography determined were identified by MALDI-TOF-MS/MS.The sequence,which may contain oligopeptide sequences,were TC-,-RE,-HE,DS-,and NM-.The oligopeptide sequence which were extracted by anion exchange resin were also determined as ER(Glu-Arg,304.0973 Da)?DVD(Asp-Val-Asp,348.1124 Da).?DPC(Asp-Pro-Cys,334.1015 Da).?WF(Trp-Phe,352.0688 Da).?DVC(Asp-Val-Cys,336.1543 Da),which may contain oligopeptide sequences such as-LD,-RE,-GH and-HR.From the results,the oligopeptide sequences detected had more umami amino acids and sweet amino acids.And the component treated by the anion exchange resin could effectively enrich the oligopeptide which containing the umami amino acids(Asp and Glu).