Study On The Characteristics And The Freeze-Dried Protective Effect Of The Biofilm On Nata De Coconut Of Lactic Acid Bacteria

As a new technology in the industrial production, biofilm technology currently is drawing more and more people’s attention. And many scholars have carried out a lot of in-depth study of biofilm which laid a solid foundation of the development and application of biofilm technology. As is known, the biofilm cell has more strong resistance to the antimicrobial agents, the toxic substances and adverse environment more than the planktonic cell. In the period of the detachment of biofilm, the cells are released continuously with a good activity and stability. Although the biofilm is troubling the researchers in the medical profession, it gives us an inspiration in the study of lactic acid bacteria. If we develop the lactic acid bacteria biofilm, we can apply the good biofilm characteristics in the lactic acid bacteria, thus promoting the probiotic make a greater contribution in the human life.Because of the fermentation stability and the good fermented yogurt flavor and taste, Streptococcus thermophilus and Lactobacillus bulgaricus are most basic lactic acid bacteria in the yogurt production. Nata de coconut, as a new bacterial cellulose material, has many advantages as follows:rich in fibre and mesh structure; large surface area, which afford good bacteria adhesion; good adsorption of bacteria; good mechanical strength; the wide raw material sources, low cost, low production cost. So the nata de coconut is a kind of excellent biofilm carrier. If Streptococcus thermophilus and lactobacillus Bulgaria can form a LAB biofilm in the surface of the nata de coconut, we can use the ability of releasing bacteria in the period of the detachment of biofilm to improve the efficiency of industrial production, at the same time, use the high activity of bacteria and the strong resistance to the adverse environment to improve the quality of the product. Biofilm technology, in short, if it can be successfully applied in industrial field of lactic acid bacteria, it will bring a very broad market prospect.1. We do research on the LAB biofilm on nata de coconut of Streptococcus thermophilus and Lactobacillus Bulgaria. We optimized the ultrasonic plate method which is one of quantitative detection methods of biofilm in order to guarantee the minimum damage and fall off more bacteria. And we get the optimal conditions of ultrasonic treatment:ultrasonic power 140 w, ultrasonic processing time 14 min, ultrasonic initial temperature 35℃. And in order to make the biofilm biomass reached the maximum, we choose to optimize the culture condition. The optimized culture condition of LAB biofilm on nata de coconut was:time 60h, temperature 37℃, solid-liquid ratio 1:30(g/mL), inoculation amount 2%. Under such condition, the viable count of mixed-species biofilm on nata de coconut reached the maximum of 5.79×108CFU/cm2.2. We analyze and compare the fermentation yogurt characteristics of the biofilm bacteria and the planktonic bacteria. We find that the reduce speed of fhe pH value of the biofilm group is faster, the increase speed of acidity value of the biofilm group is faster, the time of fermentation is shorter, no big difference in the viscosity of yogurt and the increase speed of viable count of the biofilm group is faster. At the same time, the sensory evaluation result shows that the yogurt fermented by the mixed-species biofilm on the nata de coconut is more acid. So these results illustrate that the biofilm lactic acid bacteria has stronger fermentation ability.3. Selon the study on bacteria survival rate of the biofilm bacteria and the planktonic bacteria in the condition of the high temperature, the acid, the bile salt, the high permeability and the artificial environment of gastrointestinal tract, we find biofilm may help to significantly increase the resistance to the severe environment. And the freeze-dried protective effect of the biofilm on the nata de coconut is superior to the single freeze-dried protective additive. The survival rate reached 55% which is 12,71 times higher than the planktonic bacteria. After the freeze-dried process, the bacteria activity of the biofilm bacteria is stronger. It shows that the reduce speed of the pH value of the biofilm group is faster, the increase speed of acidity value of the biofilm group is faster, the time of fermentation is shorter. In the storage experiment at 4℃ and 30 ℃, biofilm can effectively protect bacteria.4. We improve the whey medium and add two kinds of growth promoting factor (the carrot juice and the leaching of malt powder) in the medium. The optimized food-grade medium formula of LAB biofilm on nata de coconut was (L-1):100g whey powder,90mL carrot juice,60g leaching of malt powder 60g,850mL water. In such medium, the viable count of LAB biofilm on nata de coconut reached the maximum of 1.58×108CFU/cm2.