| Hyperuricemia caused by purine metabolism disorder is a serious threat to human health.Traditional methods of lowering uric acid require drugs that inhibit the production of uric acid,which are not only expensive but also with side effects.Lactic acid bacterium,as the normal flora in the human intestine,can regulate the metabolic processes such as blood lipids and blood glucose,degrade nucleosides in food,and competitively reduce the absorption of nucleosides by intestinal epithelial cells and with which uric acid synthesis can be reduced.Lactic acid bacterium has incomparable advantages in the treatment of hyperuricemia.In this theses,172 strains of lactic acid bacteria isolated from different sources of samples were screened by taking the degradation rate of guanosine and the inhibitory ability of xanthine oxidase,and their fermentation characteristics were investigated,laying the foundation for subsequent development and utilization.The main research contents and results are as follows.(1)Isolation and identification of lactic acid bacteria from different sources.239 strains were isolated from longevity intestine,infant intestine and traditional fermented food products,then acid production experiment and 16s rDNA identification were carried out onstrains conforming to lactic acid bacteria morphology.The results showed that 25,73 and 74 strains of lactic acid bacteria were derived respectively from longevity intestine,infant intestine and traditional fermented food products.Among strains sourced from longevity intestine and fermented food products,Lactobacillus plantarum accounted for 64.00%and 64.86%respectively,while L.rhamnosus accounted for 50.68%among strains derived from infant samples.(2)Study on the ability of lactic acid bacteria to degrade nucleosides.By investigating the degradation ability of uric acid and nucleoside in vitro of 172 strains of lactic acid bacteria,direct degradation on uric acid was not found among the 172 strains.In the determination of degradation ability of nucleoside,68.00%of the lactic acid bacteria derived from the intestine of longevity could completely degrade guanosine and inosine,which was significantly higher than the lactic acid bacteria from infant intestine(5.48%,p<0.05).A total of 56 lactic acid bacteria that could completely or almost completely degrade guanosine and inosine were obtained from the above sources,among which 16 strains of lactic acid bacteria that could completely degrade 0.72 mmol/L guanosine into guanine within 30 minutes,with the degradation rate ?1.43mmol/(L·h),including 9 strains source from intestinal and 7 strains source from fermented food.(3)Inhibition of xanthine oxidase by lactic acid bacteria.The inhibition rate of xanthine oxidase(XO)in 16 strains with relatively fast rate of nucleoside degradation was determined.The results showed that the XO inhibition rate of MRS supernatant in 9 strains was higher than 90%,and that of 11 strains fermented endive extract was higher than 80%.L.plantarum S7BA,56A and 67A sources from intestine of longevity,L.plantarum fA and wy02A from traditional fermented food products and L fermentum Q23A from the intestinal tract of infant intestine were highlighted through the comprehensive screening by the XO inhibition rates of the fermented endive extract.Among them,the most effective ones were L.plantarum S7BA and L fermentum Q23A,whose XO inhibition rates were 95.25%and 96.56%in the MRS fermentation broth,and 96.22%and 90.27%in the endive fermentation broth,respectively.(4)Study on dairy fermentation characteristics of screened strains.From the above 6 strains in the fermentation characteristics of skim milk,there are 5 strains besides L.plantarum 56A could get the skim milk system curded within 48 h.The pH values of Q23 A and 67A were 4.77 and 4.88,the titration acidity was 110.89°T and 93.81°T at the time of 48 h,and the viscosity was 644.00 mPa.s and 564.33 mPa.s,L.plantarum 67A showed the highest water holding power with 49.14%among the strains tested. |
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