The Rule Of Nitrite Change, Isolation And Fermentation Characteristics Study Of Related Bacteria From Fermented Carrot

The new brine and aged brine was used to ferment carrot. We analysised the formation and degradation of nitrite both in new brine and aged brine fermented carrot. Nitrate-reducing bacteria and lactic acid bacteria with nitrite degradation ability were isolated and screened. Then the factors affected nitrate reducing and nitrite degradation was studied. These results could have great theory meaning for improving the safety and processing of fermented vegetable in china. The main conclusions are following:1. We studied nitrate and nitrite content of new brine and aged brine and their fermented carrot. We got that the nitrate content in carrot was gradually reduced. Both of nitrate content in carrot and their brine reduce to96mg/kg below in third day. Nitrite content was increasing while the nitrate content was reducing. The highest PCN formed at second day reaching to65mg/kg in new brine carrot. Nitrite content in new brine carrot was as18.6times as that in aged brine carrot. The PCN in new brine was164mg/kg while128mg/kg in aged brine.2. We studied the nitrate reductase (NR) activity, nitrite reductase activity (NIR) and microbes change rule of carrot and their brines. We got that nitrate reductase activity in new brine and aged brine were both higher than that in carrot. There was significant and positive correlation between nitrite content and nitrate reductase activity (r=0.749, p=0.01). The formation of nitrite in brine was due to the NR in microbes. During the fermentation period, Nitrite reductase (NIR) in microbes was higher than that in carrot. Correlation between nitrite content and nitrite reductase activity was analysised, the result indicated that they was positive correlation between the two(r=-0.999, p=0.022). The degradation of nitrite in brine was due to the NIR in microbes. There is correlation between microbes and nitrite content (r=0.885, p=0.046). Then, the organic acid caused the nitrite reduction was studied, Lactic acid has the highest nitrite degradation activity.Two nitrate reducing bacteria were screened by the dermination of conversion ability of nitrate to nitrite. According to the biochemical and molecular identification, E5was identified as Enterobacter cloacae, E6was Klebsiella oxytoca. The fermentation characteristic of Enterobacter cloacae was studied. The optimum pH, temperature were5.5and37℃, when salt concentration below6%and nitrate concentration was0.5%, the nitrate reducing ability was high. In the process of fermented vegetable should be not in this fermentation condition.Three strains of lactic acid bacteria with strong ability to degrade nitrite were isolated from fermented carrot. Through the physiology and biochemisty experiment, R5was Leuconostoc mesenteroides and R2, R4was Weissella sp. The effect factors of the nitrite-degeneration ability were studied. The Leuconostoc mesenteroides have high temperature resistance, the appropriate temperature was20～37℃, the nitrite-degeneration ability was higher in the high temperature than that in the low temperature. When salt concentration was above8%, the growth of strain was inhibited. The optimum pH was5.5, the optimum nitrite concentration was200mg/kg; the most optimum incubation period was12～24hours.