The Method Of Removal Of Cd²⁺ And Pb²⁺ In Apple Juice By Magnetic Microspheres Of Inactivated Lactic Acid Bacteria

Cadmium and lead are highly toxic metals owing to their tendency to accumulate in the vital organs of humans and animals.People are exposed to them primarily through food and water.Microbial adsorption is a faster and more advanced method of removing heavy metals.The biological treatment of heavy metals contaminated with food,foodstuffs and the production in the process of transportation can only use food safe microorganisms.At present,lactic acid bacteria?LAB?are food microbiology to remove heavy metal ions in food or drinking water has aroused people's attention,in addition to Saccharomyces cerevisiae.Lactic acid bacteria are food-grade microorganisms which can be generally recognized as safe.They are capable of binding and removing heavy metals such as cadmium and lead in vitro.However,there are some difficulties in the separation of adsorbents after removal of heavy metals,and the low removal rate in low pH conditions,such as apple juice.This study has done a preliminary study to solve these problems.twelve lactic acid bacteria strains were investigated to obtain the most efficiency strain on adsorption of Pb²⁺and Cd²⁺in apple juice.Magnetic Fe₃O₄ lactic acid bacteria biomass?MB?was prepared by combining lactic acid bacteria biomass and nano-Fe₃O₄ using glutaraldehyde as a cross-link agent,and was chemically treated with ethylenediaminetetraacetic dianhydride?EDTAD?.The EDTAD-treated magnetic Fe₃O₄ lactic acid bacteria biomass?EMB?characteristics and biosorption mechanism were examined by SEM,XPS,Fourier transform infrared spectroscopy?FTIR?.The effect of different factors,including EMB dosage,initial concentration of Pb²⁺and Cd²⁺,biosorption time and biosorption temperature,on biosorption rate were assayed.In addition,the biosorption conditions were optimized.The main results of study were as follows:?1?the most efficiency strain?L23139?was selected from twelve lactic acid bacteria strains to further study by comparing the biomass,adsorption rate and adsorption capacity of Pb²⁺and Cd²⁺in apple juice.?2?Magnetic Fe₃O₄ lactic acid bacteria biomass?MB?was prepared by combining lactic acid bacteria biomass and nano-Fe₃O₄ using glutaraldehyde as a cross-link agent,and was chemically treated with three methods that ethylenediaminetetraacetic dianhydride?EDTAD?,poly?acrylic acid?,poly?amic acid?,respectively.And the most efficiency chemically treated MB?EMB?was selected to further study by comparing the adsorption rate and adsorption capacity of Pb²⁺and Cd²⁺in apple juice.The EMB characteristics and biosorption mechanism were examined by SEM,XPS,FTIR.The results revealed that the EFB possessed not only the superparamagnetic characteristic of nano-Fe₃O₄,but EDTA is modified on the biomass through the acylation reaction.After After analysis of FTIR.these changes indicate that the hydroxyl/amino,carboxyl,amide groups on the EMB were mainly involved in the adsorption process of metal ions in various degrees.Comparisons of°Brix,total sugar,total acidity,clarity and color value of apple juice before and after EMB biosorption.These results indicate that after treatment of EMB will not change the quality of apple juice.?3?The effect of different factors,including EMB dosage,initial concentration of Pb²⁺and Cd²⁺,biosorption time and biosorption temperature,on biosorption rate were investigated.In addition,the biosorption conditions were optimized.The optimum adsorption conditions of Pb²⁺in apple juice were as follows:EMB dosage,14.68 mg;initial concentration of Pb²⁺,0.88 mg/L;biosorption time,38 min.The optimum adsorption conditions of Cd²⁺in apple juice were as follows:EMB dosage,25 mg;initial concentration of Pb²⁺,0.44 mg/L;biosorption time,65 min.?4?The adsorption and desorption cycles of Pb²⁺,Cd²⁺were repeated thrice using eluents of 0.1 mol/L HCl.Metal recovery efficiency of EMB for Pb²⁺,Cd²⁺after three consecutive adsorption/desorption cycles,indicating that the EMB is an effective and reusable adsorbent and that HCl are good eluents of metal ions.