| In recent years,the problem of nitrite safety has remained a hot research topic.In this study,a strain of lactic acid bacteria with the ability to efficiently degrade nitrite was selected from 197 strains of lactic acid bacteria isolated from traditional fermented dairy products in Mongolia,and the growth characteristics of acid and salt tolerance were studied.Nitrite reductases(NiRs)were used for separation,purification and enzymatic properties,and the selected dominant strains were used in kimchi fermentation.The results are as follows:1.From the 197 strains of lactic acid bacteria isolated from traditional fermented dairy products in Mongolia,one strain of lactic acid bacteria with a strong ability to degrade nitrite was selected,and its number was 36.Through morphological observation,sugar fermentation experiment and 16S rDNA gene sequence analysis,the length of 16S rDNA gene sequence of strain 36 is 1464bp,the accession number is MN611150,and it is identified as Lactobacillus plantarum,and has good acid and salt tolerance.2.The fermentation broth of strain 36 undergoes separation and purification steps such as centrifugation,cell disruption,ammonium sulfate fractionation,dialysis,lyophilization,ion exchange chromatography,and Sephadex G-150 gel chromatography.The nitrite reductase rate was 15.5%.The enzymatic properties of the nitrite reductase were studied and found that the optimum temperature of the enzyme was 50?,and the enzyme activity was still 69%at the optimum temperature for 6 h,Indicating that the enzyme has good heat resistance;the optimal pH is 6.5,which is relatively stable in the range of pH 5.5-7;Fe2+and Fe3+ can be used as enzyme activators to increase enzyme activity,and the concentration is 10 mmol/L,The enzyme has the greatest promoting effect,and Fe2+ has the strongest activating effect,and Ba2+and K+have inhibitory effect on the enzyme at low concentration(1 mmol/L)and medium concentration(5 mmol/L);EDTA has no significant effect on NiRs enzyme activity.The Km value of the enzyme kinetic parameters was 7.79 mM and the Vmax value was 5.84 mg/L min.The molecular weight of the enzyme was determined to be 47.8 kD by SDS-PAGE electrophoresis analysis.3.In the analysis of pH value and total acid,inoculated with fermented pickle(experimental group)on the 3rd day of fermentation,the pH value dropped to 3.36,and then gradually decreased to stabilize around pH 3.0,while the pH of naturally fermented pickle(control group)The value of fermentation decreased to below 3.5 on the 7th day,and then slowly decreased.The total acid in pickle reached the highest value in the experimental group on day 5 at 6.14 g/kg,while the total acid content in the control group reached the highest value on day 7 at 4.01 g/kg.36 can significantly shorten the fermentation cycle of pickle.4.In the analysis of the number of lactic acid bacteria and the content of nitrite,the number of lactic acid bacteria in the experimental group reached the highest value at the 7th day,which was 9.55X109 CFU/mL,while the number of lactic acid bacteria reached the highest value in the control group until the 3rd day.1.45X108 CFU/mL.The peak of nitrite content in the experimental group appeared on day 1 at 2.25 mg/kg,and reached a lower level(1.18±0.29 mg/kg)after fermentation to day 5;the peak of nitrite in the control group appeared on 3 d,15.00 mg/kg;fermentation until the 7th day is basically stable(2.25±0.54 mg/kg),indicating that inoculation with Lactobacillus plantarum 36 can increase the number of lactic acid bacteria in pickle,reduce the content of nitrite,and increase the consumption of pickle safety.But overall,there is no significant difference in sensory indicators between fermented pickle inoculated with Lactobacillus plantarum 36 and naturally fermented pickle. |
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