Study On The Changes Of Biogenic Amines In Douchi By Pure Starter-making With Mould During The Fermentation Process

Douchi is a kind of traditional fermented condiment made from soybean or black bean,which is made by mixing,soaking,cooking,starter-making,mixing and post-fermenting processes.Because of its high nutritional value,edible and medicinal value and unique flavor,it is deeply loved by the public.At present,the research on Douchi mainly focuses on the isolation and identification of microorganisms,nutrition and flavor composition.With the improvement of public awareness of food nutrition and safety,biogenic amines in traditional fermented foods have attracted more and more attention.However,there are few reports on biogenic amines in Douchi by pure fermentation.In view of this,the experiment first evaluated the amine-producing ability of 6 strains,they were Mucor racemosus,Actinomucor elegans,Mucor wutungkiao,Aspergillus oryzae 2339(HuNiang 3.042),Aspergillus oryzae 41380 and Aspergillus oryzae 40188.On this basis,the traditional and rapid post-fermentation methods were used to product Douchi by simulated fermentation with 6 pure strains,respectively.The content of biogenic amines,the activity of amino acid decarboxylase and the related physical and chemical indexes in the process of starter-making and post-fermentation were dynamically tracked.The aim is to provide some basic theoretical data for the actual production of Douchi and the control of biogenic amines.The main results were as follows.1.The ability to produce biogenic amines of 6 strains(Mucor and Aspergillus oryzae)was analyzed by four methods including microbial method,high performance liquid chromatography(HPLC),molecular biology technology(PCR)and the enzyme technology.The results showed that the four methods obtained similar results.Six strains could produce tyramine.Actinomucor elegans and 3 strains of Aspergillus oryzae could produce tryptamine.Three strains of Aspergillus oryzae could produce putrescine.Only Mucor racemosus had histidine decarboxylase activity.Whether mold metabolism produced biogenic amines was not species-specific,but strains-specific.In other words,the ability to produce amines of different strains of the same species was different.2.Six pure strains of Mucor racemosus(ZZ),Actinomucor elegans(YZ),Mucor wutungkiao(WTQ),Aspergillus oryzae 2339(MQA),Aspergillus oryzae 41380(MQB)and Aspergillus oryzae 40188(MQC)were used to product Douchi by rapid post-fermentation.The changes of species and contents of biogenic amines and the related physical and chemical indexes during fermentation process were dynamically tracked.The results were as follows:(1)In the stage of pure starter-making,the water content of Douchi in each test group decreased to some extent.The content of total acid increased at first and then decreased,while the corresponding pH value(except YZ group)decreased first and then increased.And the content of amino acid nitrogen and related free amino acids increased gradually.During the rapid post-fermentation process,the water content of Douchi of each test group was almost unchanged at about 45%,and the pH value showed a downward trend as a whole.while the content of total acid,AAN and related FAAs increased rapidly and then tended to be flat.(2)The raw material Soybean were found to contain putrescine,cadaverine,spermidine and spermine.In the period of pure starter-making,putrescine,cadaverine,spermidine,spermine and tyramine were detected in all groups,but only a little histamine was detected in ZZ group.Only putrescine and spermidine are detected in Douchi of each test group,and the histamine and tyramine are not detected during rapid post-fermentation process.At the end of post-fermentation,the total content of biogenic amines in each test group was much smaller than 900mg/kg,and decreased in the following order:MQA>MQC>MQB>ZZ>WTQ>YZ.In DZ group,putrescine,cadaverine,spermidine and spermidine were detected,and the contents of them were not significantly changed.The change trend of amino acid decarboxylase activity in each group was basically the same as that of the corresponding biogenic amines content.(3)During Douchi fermentation process,there was no significant correlation between the content of free amino acid and the accumulation of biogenic amines in each group.The correlation between water content and biogenic amines was not significant,but there was a significant correlation between pH value,total acid AAN and cadaverine,spermidine,spermine and TBA.3.The Mucor racemosus(ZZ)and Aspergillus oryzae 2339(MQA)were used for traditional fermentation of Douchi.And the changes of species and contents of biogenic amines and the related physical and chemical indexes were dynamically tracked during traditional post-fermentation process.The results were as follows:(1)During the traditional post-fermentation process,the water content of DZ,MQA and ZZ groups remained basically unchanged.The content of total acid increased gradually and the pH value decreased as a whole.The content of AAN and related FAAs were basically the same trend,all of which increased at first and then to be flat.(2)During the traditional post-fermentation process,four biogenic amines of putrescine,cadaverine,spermidine and spermidine were detected in DZ group and the changes of content was not obvious.The biogenic amines in MQA group gradually reduced from four biogenic amines of putrescine,2-phenylethylamine,spermidine and spermine to putrescine and 2-phenylethylamine.And during the whole post-fermentation process,the content of putrescine changed slightly(46.10~57.73mg/kg),while the content of 2-phenylethylamine increased from undetectable to 222.04 mg/kg.Three biogenic amines including putrescine,spermidine and tyramine were detected in ZZ group.And the change of putrescine content is relatively low(8.35~11.63mg/kg).The content of spermidine decreased gradually,while tyramine increased from the initial undetectable to 63.68mg/kg.The change trend of amino acid decarboxylase activity in each group was basically the same as that of the corresponding biogenic amines content during the traditional post-fermentation process.(3)The correlation analysis showed that there was no significant correlation between phenylalanine and 2-phenylethylamine,while the content of arginine was negatively correlated with the accumulation of spermidine and spermine during traditional post-fermentation process.There was no correlation between water content and BAs,while there was a significant correlation between pH value,total acid,AAN content and putrescine,2-phenylethylamine,spermidine,spermine TBA and BAI.4.Compared with two kinds of post-fermentation methods,the results showed that MQA-CT Douchi contained putrescine and 2-phenylethylamine,while putrescine and spermidine were detected in MQA-KS Douchi,and the content of MQA-CT Douchi TBA is 5.20 times higher than that of MQA-KS.Compared with putrescine and spermidine contained in ZZ-KS Douchi,tyramidine was added to ZZ-CT Douchi.And the content of TBA of ZZ-CT was 2.26 times higher than that of ZZ-KS.Therefore,the contents and species of biogenic amines in the Douchi products by fast post-fermentation were lower than those by traditional post-fermentation.