| Lactic acid bacteria(LAB) are widely distributed in nature and exist naturally as indigenous microflora of Gram-positive bacteria in raw milk and play an important role in many food and feed fermentations. LAB include Lactobacillus, Lactococcus, Pediococcus and Leuconostoc, et al. They strongly determine the flavour, texture and frequently the nutritional value of food and feed products. It is very difficult to separate and store lactic acid bacteria. Lactic acid bacteria separated from Direct Vat Set (DVS) can only subculture 3 times. There hasn't any report on the genetic stability of lactic acid bacteria during subculture and storage recently. This study evaluated the genetic stability of the 3 lactic acid bacteria strains which were separated from DVS during subculture and storage by the following aspects: DNA patterns changes of RAPD, the whole cell protein SDS-PAGE, fermentation properties, morphological features.The results discovered that Streptococcus thermophilus and Lactobacillus 1 could be subcultured in improved PY medium for 15 times; Lactobacillus 2 could be only subcutured 10 times. The RAPD patterns, morphological features, SDS-PAGE, fermentation properties of Streptococcus thermophilus didn't change a lot during 4℃ storage; Streptococcus thermophilus could be stored in 4℃ for 30d; Lactobacillus 1 and Lactobacillus 2 could be stored in 4℃ for 15d; During -80℃ storage Streptococcus thermophilus could be stored for 30d while Lactobacillus 1 and Lactobacillus 2 could be stored for 15d without much change; The best choice to store lactic acid bacteria separated from DVS for a long time is by lyophilization.The present study has set up the methods to subculture and store lactic acid bacteria strains separated from DVS through morphology obsearvation , fermentation properties ,SDS-PAGE and RAPD analysis. This is the first time to use RAPD technique as a tool to analysis LAB strains' property change when they are subcultured and stored.
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