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Isolation Of Lactobacillus From Pickles And Their Adsorption Of Heavy Metals

Posted on:2019-05-25Degree:MasterType:Thesis
Country:ChinaCandidate:R LiFull Text:PDF
GTID:2370330566474536Subject:Food Science and Engineering
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With the rapid development of industrialization in the world,a large number of heavy metals have entered the natural environment where human beings rely on,causing serious heavy metal pollution.At present,most of the methods for dealing with heavy metal pollution are physical methods and chemical methods.Such methods not only invest too much,have higher costs,but also easily introduce secondary pollution,which brings serious problems to human production and life.The biological treatment method has become a research hotspot of heavy metal pollution in the current processing environment with its highly efficient and low-energy treatment mode.The biological treatment method has shown great potential in the microbiological adsorption method with advantages of small individuals,rapid propagation,high adsorption rate,and large quantities.Lactic acid bacteria are widely recognized as a food-grade microorganism in the human intestine,which is widely recognized in the human intestine.In this study,three plants were obtained from the kimchi purchased from farmers'households around a waste iron and steel plant in Sichuan.Suspected of the lactic acid bacteria strains P1,P2,and P3,after screening,the strain P1 was found to be more tolerant to heavy metals than P2 and P3.The strain P1 was selected as the dominant strain for subsequent adsorption and simulated gastrointestinal fluid tolerance determination.Using traditional physiological and biochemical identification,MALDI-TOF MS identification and 16S rDNA analysis,the strain was initially identified as a Lactobacillus plantarum belonging to the genus Lactobacillus and named Lactobacillus plantarum P1.The colony of this strain was milky white in shape with smooth edges and a smooth,moist surface.The colonies were viscous and raised in the middle without diffusion.In order to improve the productivity of the bacteria and reduce the production cost,this experiment optimized the optimal growth conditions of Lactobacillus plantarum P1.The results showed that the strain was in logarithmic growth phase within 6-15 hours of culture.At this time,the growth rate of the strain was the fastest,and the strain quality was the best.Using the single factor experiment,it was found that the optimal amount of the seed fluid was 3%,the most suitable initial pH for growth was 6.2,and the optimum growth temperature was 37°C.Under these conditions,response surface methodology was used to optimize the culture conditions to achieve high density culture.The experimental results showed that the initial inoculation amount,initial pH,the influence of initial inoculation amount ~2,initial pH~2 and culture temperature ~2 on the growth of the strain were all significant,and the interactions between the factors were not significant,indicating the experimental factors.The quadratic relationship between the growth of the bacteria and the interaction between the factors was small.The best growth conditions of the strain Lactobacillus plantarum P1 were predicted by the model:the initial inoculum size was 3.2%,the initial pH was 6.32,and the culture temperature was 37.1°C.Under this condition,the predicted number of lactic acid bacteria can reach8.79 log10cfu/mL.This experiment proves the effectiveness of the model by verifying the experiment with the best conditions.The bacteria as a biosorbent had good tolerance and adsorption performance to Pb(II),Cr(VI)and Cu(II).The influencing factors showed that the bacteria had Pb(II)and Cr(VI).The tolerances of Cu(II)and Cu(II)were 6.67 mmol·L-1,0.67 mmol·L-1and 2.17 mmol·L-1,respectively;the optimum initial pH values??were 4,6,and 6respectively;The initial ion concentrations were 100 mg/L,100 mg/L,and 50 mg/L,respectively;the optimal additions were 3 g/L,6 g/L,and 5 g/L,respectively;the optimal adsorption time was 12 h.,2 h and 8 h.The adsorption rates of Pb(II),Cr(VI)and Cu(II)at the initial ion concentration of 100 mg/L reached up to 96%,61%and49%.However,its tolerance to heavy metals has no significant correlation with the adsorption of heavy metals.In order to ensure that the strain Lactobacillus plantarum P1 can play a probiotic role in the human intestinal tract,the bacteria should have a strong ability to tolerate gastrointestinal fluids.The low pH value in human gastric juice and the high bile salt content in intestinal fluid become important barriers that can affect the activity of the bacteria after entering the gastrointestinal tract,so this experiment will make the bacteria tolerant in the simulated gastrointestinal environment.The assay showed that the strain was resistant to bile salts.The strain was cultured in the presence of 0.2%,0.3%,0.4%,and 0.5%bile salts in 0.5,1,2,3 hours,the survival rate was kept at a high level,and the survival rate could reach 75.3%at 3%bile salt concentration for 2 h.After3h incubation in simulated gastric fluid(pH=3),the survival rate can reach about73.34%.The survival rate in the simulated intestinal fluid(pH=8)after 8 h can reach73.88%.Therefore,the fungus has a strong ability to tolerate gastrointestinal fluids,can ensure that a certain number of viable cells pass through the gastric acid environment to reach the intestinal tract,has the potential for colonization in the human body,and can be used as a new lactic acid bacteria species in containing Lactobacillus foods,such as yoghurt,beans,grains and other lactic acid fermentation products or feed formulations.
Keywords/Search Tags:lactic acid bacteria, high-density culture, heavy metal, adsorption, tolerance
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