| It is a revolution to traditional natural fermentation that uses pure strain inoculation in lactic acid fermentation to make fermented vegetable, and it is a symbol of fermentation technology's modernization.In this study some strains of lactic acid bacteria would be screened for the development of fermentative vegetables with a low NaCl concentration?%). In the vegetable fermentation, NaCl not only gives products flavor, but also inhibits the growth of spoilage organism. So if NaCl concentration is lowed, some other methods must be used in order to inhibit the growth of spoilage organism. In this case , our research efforts have focused on the use of a bacteriocin nisin to inhibit them. Nisin is a bacteriocidal polypetide produced by lactococcus lactis subsp. lactis and is a readily available bacteriocin that has been approved for use in some foods in many countries /regions. But nisin is active against gram-positive bacteria including not only many spoilage organism but also lactic acid bacteria such as leuconostoc and lactobacillus species. Some lactic acid bacteria that are resistant to nisin must be isolated firstly so that nisin added not only can inhibits the growth of spoilage organism but also does not affect the fermentative progress.In this paper two high nisin-resistant strains were screened, and the optimum process parameters for fermentation pickle were studied. The main results were given as follows:1. Two strains that are resistant to nisin with high levels (up to 2000IU/ml in MRS broth ) were screened from 362 strains. One strain Ls-5105 isolated from pickles was systematically identified as leuconostoc mesenteroides subsp. mesenteroides on the basis of morphology, physiological and biochemical features with modern analytical methods and classical methods. Another strain Lb-31010 was lactobacillus plantarum obtained from our laboratory.2. The dynamics of strain Ls-5105 and Lb-31010 in MRS broth with or without 2000 IU/ml nisin including the growth, biomass, acid-producing ability, and pH value was studied. The growth of two strains were slightly inhibited at the initial stage in the presence of nisin. After 32h, the inhibition was little observed. And the effects of environment factors such as pH value,NaCl concentration, temperature on the growth of two strains were studied. The results showed that for the strain Ls-5105 , the optinum temperature and pH were 25-30 and 6.0-7.0; no growth in 5% NaCl respectively. For the strain Lb-31010, the optinum temperature and pH was 35-37 and 5. 0-7. 0, no growth in 8% NaCl respectively.3. The mechanism of nisin-resistance of two strains was studied with the measurment of residual nisin levels, production of the antimicrobial activities, and plasmid curing experiment. The results were given as follows: nisin degradation wasnot observed, no antimicrobial substance was produced, and the nisin-resistance of two strains after acridine organge treatment did not change clearly.4. The effect of various factors on vegetable fermentation with nisin and nisin-resistant strains Ls-5105&Lb~31010 was studied in the experiment with orthogonal design. The optimum fermentative conditions were given as follows: inoculation load 5%, Ls-5105/Lb-31010=1:1, Nisin 150mg/kg, salt 2%, sugar 3%, kept at 30 for 5 days. Total bacterial counts , lactic acid bacteria, pH value, titrated acid coupled with the flavor after fermentation were also studied during pickle fermentation at the best fermentative condition.
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