Investigation On Off-flavor Substances And Salty Peptides In Various Yeast Extract Products

Yeast extract(YE)is rich in amino acids,nucleotides,peptides,and other flavor substances,and is a natural nutrient,umami,and flavor enhancer.However,certain YE samples impart off-flavor that affects the quality parameters of YE.This study analyzes the odor substances in the yeast extract with gas chromatography-olfactometry-mass spectrometry(GC-O-MS)for qualitative and quantitative analysis.According to the types of odorous compounds that can be smelled in the GC-O-MS analysis as indicators,the most suitable extraction method for odor compounds in yeast extract under the current conditions is selected,there are four pre-treatment methods to choose: solid-phase microextraction(SPME),dynamic headspace sampling(DHS),solvent-assisted flavor evaporation(SAFE),and stir bar sorptive extraction(SBSE).The results show that SPME can smell 7 kinds of odorous compounds,which is the most of the 4 methods.All samples are pre-treated with SPME and then analysis with aroma extract dilution analysis.Using NIST Mass Spectral Database search,RI value verification,and standard verification,it was determined that 9 of the odor substances detected in all samples were sweaty butyric acid,sour acetic acid,rancid propionic acid as well as guaiacol corresponded to a smoky note,styrene to gasoline-like smell,n-octanal to a fatty note,o-xylene to a geranium-like smell,sterol to a caramel-like smell,and isovaleric acid to a rancid smell.According to quantitative results,the total quantity of odorous compounds of all YE products of FX-2 strain is lesser than that of YE products of DE-2 strain.In case of identical strains,the products obtained by enzymatic hydrolysis using various enzymes have fewer odor compounds.In addition,after autolysis,yeast separates the heavy phase for enzymatic hydrolysis,which produces less odorous substances than that produced by direct enzymatic hydrolysis.Moreover,the production of odorous substances in YE are inseparable from the strains,enzymes,and enzymatic processes,as well as from the altering strains in the YE production process,the use of a variety of enzymes to complex enzymatic hydrolysis,and changing enzymes.The process can impart a fuller and less odorous flavor profile to the YE.In summary,there is a small quantity of odor in yeast that primarily generated during its processing.First,the production of odorous substances in YE has a specific association with the strain.In a series of production processes,YE will derive different flavors for different yeasts used.Since the enzyme has different enzyme cleavage sites,different enzymatic hydrolysis processes will cause significant differences in the odor substances from various YEs.There are less odorous substances in YE when the cell wall is removed by centrifugation than in uncentrifuged YE,as the presence of the cell wall induces production more odorous substances by the YE.At present,the research on the taste substances in YE mainly focuses on the umami and kukomi taste peptides.Rarely,the separation and identification of salty peptide is carried out.In this study,FA31 with a salt reduction effect of up to 80% of the peptide content was carried out isolation,purification and identification of salty peptides.In this study,the peptides in FA31 were separated step by step using ultrafiltration,gel permeation chromatography,and preparative liquid chromatography,combined with sensory evaluation to find the salty components,and ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry is used to identify the peptide sequence.ESI-UPLC-Q-TOF MS/MS is used to fragment the peptide molecules,combined with the peptide chain break rule;sequences of 5 peptide were manually analyzed,which were Asp-Asp,Glu-Asp,Asp-Asp-Asp,Ser-Pro-Glu,Phe-Ile.These five salty peptides were synthesized,and sensory evaluation was performed after dissolving them in water,vegetable soup and beef broth to determine the taste characteristics.All five peptides has a salty taste.Among them,Asp-Asp and Glu-Asp has salty,umami and sour taste,Asp-Asp-Asp has salty and umami taste,Ser-Pro-Glu has a salty and sour taste,and Phe-Ile has a salty and bitter taste.Therefore,the five peptide chains analyzed are all salty peptides,which realizes the separation,purification and identification of the peptide sequence in the yeast extract.It provides a theoretical basis for the salt reduction effect of yeast extract FA31.