Effects of Co-culture of Lactobacillus casei NA-2 and Lactobacillus rhamnosus LGG on Antibacterial Activity
The application of lactic acid bacteria in food,medicine and other industry depend on their antibacterial activities.To improve antibacterial activity by optimizing the co-cultural conditions of different lactic acid bacteria,the antibacterial activity of Lactobacillus casei NA-2 was determined by double agar diffusion method using Escherichia coli K88 as indicator bacteria,and the culture system was supplemented with Lactobacillus rhamnosus LGG in order to monitor any changes in antibacterial activity.The co-culture conditions of L.casei NA-2 and L.rhamnosus LGG including inoculation ratio,culture temperature,time,aerobic,carbon and nitrogen sources and pH were optimized by single factor test.The total viable cell counts and lactic acid contents of L.casei NA-2 and L.rhamnosus LGG were detected by quantitative real-time PCR method and high performance liquid chromatography,respectively.The results showed that the antibacterial activity was significantly increased after L.rhamnose LGG was added into L.casei NA-2 for co-culture.By comparing L.casei NA-2 pure culture with co-culture without optimization in optimal co-culture conditions,it revealed increases in antibacterial activity of 20.7%and 11.0%and lactic acid production of 15.2%and 7.3%,respectively.The overal viable cell counts decreased from 2.74×108 to 1.57×108 CFU·mL-1 after co-culture conditions optimized,but the proportion of L.casei NA-2 increased from 7.0%to 65.6%.Above results provided data support for further research and application of lactic acid bacteria co-culture system.
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