Effect Of Exogenous Amino Acids On The Flavor Quality Of Pixian Broad-bean Paste And Establishment Of Sensory Evaluation Method

Pixian broad-bean paste(PXBP)is a local specialty product that enjoys worldwide reputation and is a necessary seasoning in the production of Sichuan cuisine.Flavor is one of the important factors to measure its quality.Nowadays,the research on the flavor of PXBP is still focused on the identification of flavor compounds in the fermentation process,and there are few reports on the improvement and regulation of flavor.The formation of various flavor compounds in PXBP is closely related to the metabolism of amino acids,and exogenous addition of amino acids to regulate flavor is a method worthy of discussion.In this research,the maillard reaction simulation system of amino acids and water extract of PXBP was constructed to determine the species and amount of amino acids added,and then applied to the actual fermentation system of PXBP.After that,the effects of the adding species and amount of amino acids on the physicochemical indexes and flavor of PXBP during fermentation were analyzed,and the sensory evaluation method was established to evaluate its quality.The addition of exogenous amino acids provided data for improving flavor quality,optimizing fermentation process and shortening fermentation period of PXBP.Solid phase micro-extraction-gas chromatography-mass were used to evaluate the contribution of single amino acids to the key flavor compounds in PXBP.Then selected phenylalanine,methionine,arginine,aspartic acid,lysine and leucine to build the maillard reaction simulation system of compound amino acids and water extract of PXBP.The effect of the dosages and proportions of compound amino acids to the flavor compounds in PXBP were investigated combined with sensory evaluation.Finally,the appropriate amount of amino acids was determined as follows: based on the mass of PXBP,0.0140 g aspartic acid,0.0072 g arginine,0.0010 g methionine,0.0074 g leucine,0.0048 g phenylalanine and 0.0050 g lysine were added to every 33 g PXBP.Five groups of PXBP were fermented by adding different amounts of amino acids at different fermentation stages.They were as follows: PXBP A-amino acids were added in the pre-fermentation process based on the weight of Meju,PXBP B-amino acids were added in the pre-fermentation process based on the weight of PXBP,PXBP C-without amino acids added,PXBP D-amino acids were added in the post-fermentation process based on the weight of Meju,PXBP E-amino acids were added in the post-fermentation process based on the weight of PXBP.The results showed that the total acid contents of fermented broad bean in the pre-fermentation process were reduced by the addition of exogenous amino acids.And the number of alcohols increased,the number of aldehydes and esters decreased,while the content of alcohols and aldehydes increased and the content of esters decreased.The content of amino acid nitrogen increased in Meju B,the reducing sugar conversion rate was accelerated,and the content of various flavor compounds increased.In the post-fermentation process,the total acid content of PXBP with exogenous amino acid addition in conformity with national standard,the conversion rate of reducing sugar was faster,but the content of amino nitrogen decreased.The total color value of PXBP A and PXBP B declined,while PXBP D and PXBP E increased.Adding amino acids in the pre-fermentation process promoted the accumulation of alcohols,acids,phenols,ethers and other substances in PXBP,and shorten the accumulation time of alcohols,esters,alkanes,phenols and ethers.Whereas,addition of amino acids in the post-fermentation process promoted the accumulation of aldehydes,esters,ketones and other substances in PXBP,and shorten the accumulation time of esters,ethers and other substances.Furthermore,adding amino acids coordinated the accumulation time of various flavor compounds,and formed PXBP with the most abundant flavor compounds at 50 days.Hence,the fermentation period could be shortened from 90 days to 50 days.Adding amino acids had positive effect on the formation of isovaleraldehyde,ethyl isovalerate,3-methylthiopropanol and 3-methylthiopropanal(PXBP D),benzaldehyde(PXBP D,PXBP E),nonanal and ethyl acetate(PXBP B,PXBP D,PXBP E),negative effect on the formation of styrene,nonanal and ethyl palmitate(PXBP A),and no obvious effect on the formation of isoamyl alcohol,isovaleric acid,myrcene,linalool,phenethyl alcohol,phenylacetaldehyde,ethyl nonanoate,ethyl acetate(PXBP A),ethyl butyrate,ethyl palmitate(PXBP B,PXBP D,PXBP E),ethyl 2-methylbutyrate,2,5-dimethylpyrazine,4-ethylphenol and 4-ethyl-2-methoxyphenol.The Flash Profile method and Quantitative Descriptive Analysis method were used to conduct sensory analysis of six different PXBP,so as to establish a sensory method suitable for PXBP.The comparisons were made from the description words,data reliability,sample score graph,attribute loading graph,sample clustering and correlation coefficient of the two methods,and then,the optimized Quantitative Descriptive Analysis method was established.This method was used to evaluate three common types of PXBP,red oil PXBP and frying PXBP with exogenous addition of amino acids.The results indicate that adding vegetable oil and frying could affect the sensory quality of PXBP in flavor.Cluster analysis divided PXBP A~E into AB,CD and E,because of the different amino acid adding process,the sensory quality of PXBP were different.PXBP D and PXBP E were not classified into the same category,and they showed significant differences in the properties of humidity,herbaceous,grease,particle and salty taste,etc.Therefore,amount of amino acids added in the post-fermentation process would also lead to different sensory qualities.