Screening Of Strains For Degradation Of Nitrite In Pickles And Its Degradation Mechanism

The safe control of nitrite?NIT?has always been one of the key problems in the fermentation process of pickles.This paper screened a lactic acid bacteria with high efficiency of nitrite degradation from natural fermented pickles.The factors affecting the degradation of nitrite and the degradation mechanism were studied.The results are as follows:1.75 strains of suspected lactic acid bacteria were screened from natural fermented radish.A strain of Lactobacillus plantar?m LP-7501 with high ability to degrade nitrite was screened by nitrite degradation ability test and actual fermentation test.2.Through the carbon source and nitrogen source test,the ability of LP-7501 to grow and metabolize acid and degrade nitrite in carbon source medi?m is inhibited,its utilization of the simple carbon source is monosaccharide>disaccharide>polysaccharide;when LP-7501 uses ammoni?m nitrate as a nitrogen source,the ability to grow and metabolize acid and degrade nitrite is inhibited,but the yeast extract,corn paste and peptone can promot the growth and metabolism of LP-7501and the ability to degrade nitrite;the nitrite degradation rate of LP-7501 in all three organic nitrogen media was over 99%within 72h,and the degradation rate is yeast extract>corn paste>peptone.The rate of degradation of nitrite by LP-7501 in the three organic nitrogen source media was higher than that of total acid growth,so it is speculated that there may be an enzymatic degradation pathway in the pathway of LP-7501 degradation of nitrite.According to the carbon-nitrogen source ratio test,when the amount of glucose added is 3%,the higher the amount of yeast extract added,the faster the rate of nitrite degradation by LP-7501,however,after 36 h,the degradation effect of nitrite was not much different among the groups with a carbon-nitrogen source ratio of less than 1.Through the detection of organic acid species in different samples,it can be known that LP-7501 can produce lactic acid under a single carbon source condition,and can produce a small amount of acetic acid under the conditions of fructose,sucrose and dextrin,can produce lactic acid,acetic acid,citric acid and succinic acid under the conditions of yeast extract,corn paste and peptone.These organic acids can react with nitrite to form NO and NO₂,which constitutes the acid degradation pathway of LP-7501 to degrade nitrite.3.After crude extraction,DE-52 chromatography and Sephadex G-150chromatography,2.1 mg of nitrite reductase?NiRs?with an enzyme activity of 36.72U/mg was obtained,and the purification yield was 12.8%.After electrophoresis,ICAP detection and property analysis of purified NiRs,it can be concluded that the NiRs may be trimeric Cu-NiRs with a molecular weight of about 130kDa,and the concentrations of Cu²⁺and Fe²⁺in the protein are 413mg/kg and 98.4mg/kg.The optim?m enzyme expression activity temperature of the NiRs was 35?and the pH was 6.0.Cu²⁺,Fe²⁺and Fe³⁺all promoted the enzyme activity,and Zn²⁺had a great inhibitory effect on the enzyme activity.By detecting ammoni?m nitrogen and N₂O,it was found that there was no NH₄⁺in the product of LP-7501 degradation of nitrite,and there was N₂O,so the pathway of LP-7501 enzyme to degrade nitrite was respiratory denitrification.The nitrite degradation rate curve and the N₂O gas concentration curve in the MRS reaction system are basically coincident,indicating that the degradation rate of nitrite can be basically detected by detecting the N₂O gas concentration.4.By studying the organic acids in the fermented radish,the content of oxalic acid and malic acid in the LP-7501 pure-fermented radish was lower than that in the naturally fermented radish,and the contents of lactic acid,citric acid and succinic acid were increased.Through single factor experiment on sucrose addition,salt addition,nitrogen source addition,fermentation time and fermentation temperature,based on single factor experiment,orthogonal design was designed to screen for nitrite degradation during LP-7501 actual fermentation.The optimal fermentation process is:The sucrose addition amount was 0.9%,the salt addition amount was 4%,the nitrogen source addition amount was 0.7%,the fermentation time was 84 hours,and the fermentation temperature was 30?.Under the fermentation conditions,the total acid content of the fermented radish was 0.73g/100 g,the nitrite content was 0.432 mg/kg,and the sensory score was 75 points.