Study On Identification Of Characteristic Flavor Compounds And Umami Peptides Of Four Boletus And Its Taste Mechanism

There are many kinds of wild edible fungi in Yunnan province,which have high edible and medicinal value,but the product form is relatively single,and the deep processing capacity is insufficient.These factors seriously restrict the development of wild edible mushroom in Yunnan Province.In this paper,Yunnan wild Boletus,which is the largest export volume,was selected as the research object.Firstly,the characteristic flavor components of four different Boletus species(Boletus edulis,Boletus Aereu,Boletus Auripes Pk and Boletus Rubellus Krombh)were analyzed and compared.Then,the extraction of flavor substance of Boletus edulis was optimized and compared.On this basis,the umami peptides were identified and analyzed on umami taste mechanism.The research results have a certain practical significance to enhance the added value of wild Boletus products in Yunnan,and also provide theoretical and methodological guidance for the development of other edible fungi seasonings.The main research contents and results are as follows:(1)Mushrooms from different varieties and manufacturing methods show different flavor profiles.In order to understand the sensory attributes and aroma compounds of boletus,the discrepancy of aroma profile in four varieties of boletus was determined using gas chromatography–olfactometry combined with sensory analysis,recombination experiment and partial least squares regression analysis(PLSR).Sensory analysis revealed that Boletus edulis had potent roasted and buttery attributes,Boletus Aereu exhibited woody note and Boletus Auripes Pk presented powerful floral and smoky aromas,while Boletus Rubellus Krombh showed weakness in five sensory attributes.The quantitative analysis revealed that the dominant volatiles in boletus samples were esters,aldehydes,acids,alcohols,pyrazines,ketones and phenols.A total of 42 potent aroma compounds were determined by aroma extract dilution analysis and quantitative analysis.1-Octen-3-ol and 2,5-dimethylpyrazine were the potent aroma compounds among four boletus samples.In addition,the key aroma compounds were 3-(methylthio)propionaldehyde and 2,6-dimethylpyrazine in Boletus edulis.Isovaleric acid,2,6-dimethylpyrazine,benzeneacetaldehyde and(E)-2-octenal were the key aroma compounds in Boletus aereu.In Boletus auripes Pk,isovaleric acid,3-ethylphenol and2,6-dimethylpyrazine were the key aroma compounds,while 3-methylvaleric acid,isovaleric acid and 2,3-dimethylpyrazine significantly contributed to the aroma of Boletus rubellus Krombh.Indeed,PLSR indicated that significant difference on aroma resulted from different varieties of boletus.(2)The effects of high pressure cooking and two enzymatic pretreatment methods on the release of flavor substances from Boletus edulis were studied.the results showed that the effects of three different extraction methods on the release of flavor substances were different.Compared with the blank control,three different extraction methods could promote the release of soluble sugar from Boletus edulis.Compared with cellulase and flavourzyme,the total amount of soluble sugar was lower in extracts by high-pressure cooking and alkaline protease and flavourzyme hydrolysates.In terms of organic acid,compared with the blank control,the total amount of organic acid in high pressure cooking solution increased significantly,mainly due to the significant increase in the content of malic acid,?-aminobutyric acid and succinic acid.In terms of the total amount of nucleotides,the blank control has the highest nucleotide content,indicating that several treatments are not conducive to the release of nucleotides in the extract.From the point of view of inorganic ions,Boletus edulis contains more potassium ions,which may be caused by the growth environment of the sample.As for free amino acids,the total amount of free amino acids increased after different methods,in which the most free amino acids were obtained by high pressure cooking,and the contents of umami amino acids,sweet amino acids and bitter amino acids increased most significantly.(3)The screening,taste characteristics,taste mechanism and protein source of the three kinds of processed samples of Boletus edulis were analyzed using proteomics,LC-MS/MS,computer-assisted simulation and sensory evaluation methods.421,616 and 713 peptides were identified by LC-MS/MS analysis in the blank control,high-pressure cooking and cellulase and flavorzyme hydrolysis preparations,respectively,and then umami peptides(DGF,EAP,DPY,TEWH,YDKL,HHYE,KCGQ,RNGR and YFQH)were selected based on their amino acid composition,structural characteristics and computer-aided simulation.According to the computer simulation(molecular docking)screening score,three umami peptides(DGF,HHYE and KCGQ)were selected for verification through sensory evaluation in terms of taste characteristics,threshold value,and dose structure-activity relationship.It was found that the peptides with high scores were better umami taste.The taste characteristics are more obvious.Next,through the above analysis,molecular dynamics simulations of the umami peptides DGF,HHYE and KCGQ were performed to explain their umami mechanism,and it was found that aspartic acid,glutamic acid and lysine residues play an important role in the binding of umami taste peptides to umami taste receptors.It was found that the interaction between the umami taste peptide and the umami receptor was mainly coulombic force.Finally,the main protein sources of umami peptides of Boletus edulis were fatty acid synthase subunit alpha and ribosome biogenesis protein NSA2.