| Biogenic amines(BAs)are nitrogenous organic compounds,which can be found in various fermented food.They can cause human urticaria,migraine and other allergic symptoms.Soybean paste is a typical traditional fermented food and it is made using soybean and flour as raw materials through fermentation by a variety of microbes.Due to the open fermentation environment,the interactions of various microorganisms may lead to the gradual accumulation of biogenic amines during the soybean paste fermentation,thus affecting the quality and safety of soybean paste.To ensure the quality and safety of traditional fermented foods,this study aimed to screen the biogenic amines degrading strains from bean paste samples and test the influence of different conditions,including salinity,temperature and p H on the degradation characteristics of the biogenic amines degrading strains on the degradation of histamine and tyramine.The biogenic amines degrading strains were applied in fermentation of soybean paste and the concentrations of total amine,histamine and tyramine during fermentation were monitored,which could be as a reference for the biogenic amines control of fermented soybean paste in the future.The main findings of the thesis are as follows:(1)The biogenic amines degrading strains were isolated from bean paste mash samples.In this study,the strains were preliminarily isolated by using the solid medium of biogenic amines as the sole nitrogen source(BAs)and modified MRS(MMRS).After the comprehensive study of the biogenic amines degrading ability and biogenic amines producing ability of primarily screening strains,two strains with strong biogenic amines degrading ability were isolated and identified as P.acidilactici M-28 and S.carnosus M-43.(2)The degradation characteristics of the two isolated optimal strains towards histamine and tyramine,which were relatively toxic among all biogenic amines,were tested in different conditions,including salinity,temperature and pH.The result shows that the degrading ability of P.acidilactici M-28 and S.carnosus M-43 on histamine and tyramine were relatively high between 0-9% salinity and the highest degrading percentage could reach 89.02% and 31.49%,54.46% and 35.45%,respectively.The optimum temperature for the two strains was 30?-40?,and the highest degrading percentage of histamine and tyramine could reach 65.51% and 28.06%,48.93% and 33.66%,respectively.The optimal pH for P.acidilactici M-28 degrading histamine(62.73%)and tyramine(23.78%)was pH 6,while high degrading ability of S.carnosus M-43 on histamine and tyramine were achieved when the p H was around 5-7 and the highest degrading percentage could reach 43.91%(pH 7)and 16.77%(pH 6),respectively.(3)These two optimal strains were inoculated in soybean paste fermentation separately or together.The results showed that the biogenic amines concentration of PA group(inoculated with P.acidilactici M-28),SC group(inoculated with S.carnosus M-43)and PA+SC group(inoculated with P.acidilactici M-28 and S.carnosus M-43 at a ratio of 1:1)increased at a much slower rate than that of control during the fermentation of soybean paste.After 35 days fermentation,the amino acid nitrogen concentration of soybean paste was stable.At the end of fermentation,PA+SC group showed the most effective effect in degrading biogenic amines.Compared with control,the degrading percentage of total amines,histamine and tyramine were 39.69%,12.5% and 62.59%,respectively.The flavor compounds of soybean paste were also analyzed.Compared with control,the experimental group(PA,SC,PA+SC)increased the flavor compounds,and the group PA+SC possessed the highest concentration of aldehydes and free amino acids,which could improve the flavor quality of soybean paste.Therefore,inoculated with mixed starter culture P.acidilactici M-28 and S.carnosus M-43 in soybean paste fermentation not only decrease the concentration of biogenic amines to ensure the quality and safety of soybean paste,but also improve the quality of soybean paste. |
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