Study On The Changes Of Key Enzymes And Flavoring Substances During Koji-Making Of Pixian Soybean Paste

Pixian Soybean paste(PSP)is a traditional semi-solid fermented condiment in China,which is welcomed by the general public because of its rich and unique flavor.During the production of PSP,the maturing process of Broad bean(Vicia faba L.)is actually use the enzymes and microorganisms accumulated during the cultivation of koji to decompose macromolecules such as starch and protein in the raw materials,and then metabolized amino acids,sugars,and organic acids,then form different kinds of volatile flavor substances.Therefore,the fermentation stage of sweet petals is the key stage to influence the final product quality and flavor formation of PSP.In this paper,Broad bean(Vicia faba L.)in different stages of PSP koji-making process were taken as the main research object,analyzed the changes of the main key enzyme system,starch,protein and volatile flavor.The specific contents and results are as follows:Firstly,tracking the changes of the secondary structure of protein and five key enzymes.The results showed that protease activity fluctuated between 709.8 U/g and 1183.4 U/g,the activity of pectinase fluctuated between 12.33 U/g and 36.98 U/g,lipase and ?-amylase activity decreased from 99.3 U/g and 38.9 U/g to 10.9 U/g and 3.4 U/g,respectively;cellulase showed an overall upward trend,but its activity was low,with an average activity of 1.30 U/g.The secondary structure of sweet petal protein is mainly ?-helix,and preliminarily speculate the correlation between key enzyme activities and secondary structure.These reflect the changes of protein secondary structure and enzyme system of PSP in the early koji-making and fermentation,which has certain guiding significance for the production of PSP.Simultaneously analyzed the six basic components such as protein and total acid,as well as the microstructure changes of bio-macromolecule starch and protein.The results indicate that the content of protein,total nitrogen and total sugar decreased and remained at about13.88%,2.22% and 23.8%,respectively,total acid and fat changed little,with the average content of 0.66% and 1.53%;During the fermentation process,the koji starch granules gradually aggregated,and the protein molecules also aggregated to form a dense network structure.These changes reflect the inherent characteristics of the material conversion of PSP in the early koji-making fermentation.Then determining the change of volatile aromatic substance in koji at four different fermentation stages by headspace solid-phase microextraction combined with advanced gas chromatography-mass spectrometry analysis technology.It showed that here are detected a total of 14 alcohols,11 aldehydes,6 ketones,12 esters,7 acids,9 alkanes,12 alkenes,4phenols,6 heterocyclic substances and 7 other substances,among them,the highest contentswere(+)-limonene(0 d,42.12%),furfuryl alcohol(8 d,25.05%?16 d,24.44%?24 d,28.74%).With the progress of fermentation,the relative content of 5 kinds of substances such as alcohol,aldehyde,ester,acid and phenol increased significantly,while the relative contents of 3 kinds of substances such as alkane,olefin and heterocycle gradually decreased.Finally,the electronic nose technology was used to analyze the dynamic changes of the volatile flavor of koji with different fermentation time.Loadings analysis,principal component analysis,linear discriminant analysis were used to classify and analyze the sweet petals with different fermentation times.It showed that alcohols,aldehydes,ketones and methyl groups were the main volatile components of koji,and the linear discriminant analysis could distinguish the sweet petals with different fermentation time.