| Biogenic amines(BAs)are produced by microorganisms in fermented foods such as wine through decarboxylation.The safety of BAs has become an increasingly widespread concern because of their dangerous cardiovascular effects at high concentrations.It was shown that the use of biological control during food fermentation can effectively reduce BAs in fermented foods without compromising the flavour.Lactic acid bacteria is the dominant strain in MLF of wine.Therefore,in this thesis,aimed to screen lactic acid bacteria with good BAs degradation ability was selected from wine and white wine grains,and test its growth characteristics and BAs degradation characteristics of different conditions,including pH,ethanol and temperature.The BAs degrading strains were applied in fermentation of wine,It also clarifies the degradation of BAs,the fermentation capacity and the effect on wine quality,and provides a theoretical basis for the regulation of biogenic amines in the process of wine fermentation.The lactic acid bacteria freeze-dried bacterial powder was also prepared by response surface methodology to study its storage stability and provide data support for the development of fermenters.The main research conclusions of the thesis are as follows:1.Screening of the biogenic amines degrading LAB.The BAs(chromogenic)medium was used to initially screen BAs degrading strains from wine and liquor glycine.HPLC was used to determine the degradation rate of biogenic amines in MRS liquid medium containing six BAs,after the comprehensive study of the BAs degrading ability of primarily screening strains,two strains with strong BAs degrading ability were isolated and identified as Lactobacillus plantarum NXU-Q7 and Lactiplantibacillus plantarum NXU-Q12.2.The growth and characterization of BAs degradation by Lactobacillus plantarum under different environmental conditions,including pH,ethanol and temperature.It was found that under normal culture conditions,the acid-producing capacity of L.plantarum NXU-Q12 was slightly better than that of L.plantarum NXU-Q7.The two strains can grow and have BAs degrading ability under different pH,ethanol,SO2 and temperature conditions and have the ability to degrade BAs,With the change of environmental conditions,the growth activity of both strains and the ability to degrade BAs are simultaneously inhibited.At pH 3.0,14%ethanol,80 mg/L SO2 and 18℃,the degradation capacity of histamine,tyramine and tryptamine,L.plantarum NXU-Q12 was better than L.plantarum NXU-Q7.Therefore,L.plantarum NXU-Q12 was selected as the final excellent biogenic amine-degrading stain.3.L.plantarum NXU-Q12 was inoculated in wine processing.The results showed that the physicochemical indicators of the wine samples fermented with L.plantarum NXU-Q12 complied with the national standards.The non-significant difference in acid reduction ability of L.plantarum NXUQ12 compared to commercial Lactobacillus O.oenil indicates that this strain has good fermentation ability.Meanwhile,the total biogenic amine degradation rate of the two wine samples(Cabernet Sauvignon wine and Matheran wine)fermented by L.plantarum NXU-Q12 was 31.07%and 41.51%compared to commercial Lactobacillus O.oenil.The flavour components of the wines were measured at the end of MLF and the results showed that L.plantarum NXU-Q12 increased the content and variety of some esters and higher alcohols in both wine samples,imparting floral and woody aromas as well as fruity flavours such as pineapple and pear to the wines.Thus,L.plantarum NXU-Q12 was not only effective in controlling the biogenic amine content of the wines,but also had good wine fermentation potential.4.The preparation of L.plantarum NXU-Q12 freeze-dried bacterial powder.The response surface method was used to optimize the formulation of freeze-dried L.plantarum NXU-Q12 freeze-protectant,and to study the collection conditions of the bacterial bodies,the re-solubilization conditions and the storage stability of the powder.The experimental results were:the best collection condition was 4500 r/min and centrifugation for 10 min,the optimum formulation of the lyophilised powder protectant was 9.19%skimmed milk,8.30%alginate and 8.09%monosodium glutamate.86.57%bacterial survival was achieved in this formulation,the optimum re-solubilisation conditions were 30 min in the original protective medium liquid environment and the optimum storage temperature was 4℃. |
