Experimental Investigation On Nitrite Degradation By Lactic Acid Bacteria And Application In Acid Radish

The excessive of nitrite is one of the most important problem which needed to be solvedin fermented products. In order to find out the mechanism of LAB degrading nitrite, weinvestigated effects of different strains of LAB species, defined medium and pH on thechanging of nitrite contents. The final results were also applied in fermented radish. Theresults are as follows:1.The strains of four LAB species were cultivated at MRS, their ability of nitritedegradation was that: LP＞LC＞LH＞LM. And the nitrite degradation rate after72hours’fermentation was98.19%,97.84%,95.59%and38.79%respectively. The results alsoindicated that the nitrite degradation rate is high if the total acidity of the solution is high.Among the tested LAB, LP showed great potential of degrading nitrite as well as good growthin MRS culture, so we chose LP as the test strain;2. Growth and nitrite reduction activity is restrained in mediums that only composeddifferent3%carbon source, the final degradation rate was less than8.20%after72h. Theresults indicated that the addition of carbon source and organic nitrogen source was able tomeet nutritional requirements of lactic acid bacteria and yields rapid degradation of nitrite,with2%yeast extract and2%enzymatically soy isolated protein degraded96.44%and97.18%of the nitrite in solution. Their final pH could reach3.84and3.89respectively. Andthe degradation rate in2%un-enzymatically soy isolated protein medium and ammoniumnitrate medium was36.44%and6.26%., their final pH reached only4.64and5.27. If adding3%glucose, the nitrite degradation rate varied directly with the amount of yeast extract. Ingeneral, the best C:N ratio of the culture was3:3for LP degrading nitrite.3. It was found that the nitrite degradation rate after72h in culture which had its pHadjusted to7.20,6.20,5.20and blank group was99.86%,53.55%,99.15%and99.84%respectively. The degradation course relied on enzymatic degradation and acid splitting whenoffered enough nutrition while each can make for significant effect of degrading. Enzymaticdegradation was restricted in low-acid solution, the optimum pH for enzymatic degradationwas about7.20. And acid splitting can be reinforced when LP was afforded to fermentsolution under pH of4.4. The nitrite peak appeared on5th day in pickled radish produced by naturalfermentation, the maximum content could reach as much as31.28mg/L. Using artificialfermentation in pickled radish can significantly reduce the content of nitrite: The nitrite peakwas shifted two days earlier and the maximum content was8.92mg/L in the blank group. Another group which had added3%glucose and3%yeast extract had few nitrites during itsfermentation, the content of nitrite was0.10~0.36mg/L.