| A DVS Gluconacetobacter xylinum composite protectve agent was developed by using freeze drying echnique. Firstly, 10% skimmed milk, 5% trehalose, 1% glutamate were screened respectively as the protective agent of G.xylinum through single factor test. Furtherly, the formula of cyprotectants for G. xylinum was optimized by central composite design (CCD). The result showed that the survival rate of the freeze-dried G. xylinum was up to a maximum of 93.346% when the cryoprotectant contained 6.4% skimmed milk, 0.075% trehalose and 0.575% glutamate. Finally, the comparative trial showed that the yields of Nata were not significant among in the starter culture adding the compound freeze-dried cryoprotectant and in the starter culture with the same concentration of living bacterium liquid. |
