| Most of Lactic acid bacteria and yeasts have the abilities about high safety and edible properties,which are widely used in foods and feeds.It has been confirmed that these two types of microorganisms can bind toxic and hazardous substances such as heavy metals,mycotoxins,plasticizers,heterocyclic amines,and dyes through adsorption,thereby reducing the harm of toxic and harmful substances to the environment or the human body.Only a few scholars have studied the adsorption of organophosphorus insecticides and herbicides by Bacillus,Pseudomonas,and lactic acid bacteria,but there is no report about lactic acid bacteria or yeasts could be used for the adsorption of pyrethroid pesticides.The pyrethroid pesticides represented by cypermethrin?CY?have been widely used pesticides in agroforestry.They are easy to accumulate in the environment and enter the human body through the food chain.The metabolites are more toxic than maternal and might cause secondary pollution.Therefore,how to use a safe and effective method to remove CY from the environment and food and reduce the harm of CY to human health has become an urgent problem to be solved.Microbial adsorption has received extensive attention due to its various types,wide sources,green,high-efficiency,and economic advantages,it has received extensive attention from scholars.In this study,Lactic acid bacteria and yeast isolated from fermented foods and feces of healthy animals were used as the microbial source,and strains with high adsorption,high tolerance to CY,and good effects in the gastrointestinal tract were selected.And explore its adsorption characteristics,mechanism,and the effect of the strain on the removal of CY in fruit and vegetable juice preliminary.The main results are as follows:?1?Screening and identification of CY adsorbing probiotics.Based on the adsorption capacity of each strain,6 strains from 282 strains of lactic acid bacteria and 5 strains from45 strains of yeast strains were selected with high adsorption rate.Combining with strains resistant to CY,and the tolerance in artificial gastrointestinal fluid,adsorption rate,and adsorption stability of the strains,re-screened 4 strains with adsorption and probiotic properties.According to morphological analysis,physiological and biochemical characteristics and 16S rDNA or 26S rDNA analysis,it was determined that the strain RS60 from pickle was Lactobacillus plantarum,and the strain D15 from pickle was Pediococcus acidilactici.The strain YS81 derived from bacon and strain HP from red wine were Saccharomyces cerevisiae.?2?Characterization of CY adsorbing probiotics.The characteristics of the adsorption of CY by probiotics were investigated,including the influence of different factors on the adsorption capacity of the bacteria,adsorption stability,adsorption ability of other substance,kinetics,and adsorption isotherm curves.The adsorption of CY by lactic acid bacteria was mainly affected by the co-cultivation time,temperature,cell concentration,and CY concentration,and the pH had little effect.Strain RS60 and D15 increased CY adsorption rate with co-cultivation time within a certain range and then reached equilibrium.Temperature and cell concentration advantageous for CY adsorption,but the adsorption rate decreased with CY concentration increasing.At pH 38,the adsorption rate did not change ovbiously.The elution rate of the complex formed by lactic acid bacteria and CY in the PBS solution was lower than that of the Tween solution.The deltamethrin,fenvalerate,cyfluthrin,and 3-phenoxybenzoic acid are adsorbed to varying degrees.The kinetic adsorption and adsorption isotherms of the strains were fitted,indicating that the process of CY adsorption by the strains was in accordance with the quasi-secondary adsorption kinetic model and the Langmuir model.The adsorption of CY by yeasts is mainly affected by the co-cultivation time,temperature,and the concentration of the bacteria.The influence of pH and CY concentrations is small.Within a certain time range,the adsorption rate of CY for strains YS81 and HP was positively correlated with time,pH had no effect on adsorption rate,and the adsorption rates of the two strains of yeast were 97.33-97.89%and 98.15-99.44%.It is not conducive to the adsorption of CY by the strains in the low temperature.The adsorption rate increases with the increase of cell concentration,but the adsorption rate does not increase significantly when the cell concentration reaches 1×109 CFU/mL.When CY is 5–100 mg/L,the adsorption rate has little change.The complex formed by yeast and CY is more stable in PBS solution than in Tween solution.It has adsorption capacity for deltamethrin,fenvalerate,cyfluthrin,and 3-phenoxybenzoic acid.The process of YS81 and HP adsorption of CY were accorded with the pseudo-secondary adsorption kinetic model and Langmuir model.?3?Mechanisms of CY adsorbing probiotics.After heat treatment,the adsorption rate of CY by strains RS60 and D15 was increased,indicated that the removal ability was not related to the cell viability.Acid and alkali treatment reduced the adsorption of CY by RS60,but the adsorption rate of D15 increased after acid treatment and did not change after alkali treatment.Lysozyme treatment can increase the adsorption capacity of D15,but it has no promoting effect on RS60.The adsorption of CY by two strains of lactic acid bacteria is not affected by proteinase K.The extracellular polysaccharides of strains RS60and D15 were all involved in adsorption,and the removal rate increased without extracellular polysaccharides.After removing the surface protein,the adsorption rate showed different changes,RS60 adsorption rate decreased,while D15 adsorption rate increased.The adsorption capacity of each cell component was measured.It was found that the cell wall was the main cell component of the strain RS60 and D15 involved in the adsorption of CY,followed by the protoplasts.The peptidoglycan played a major role in the cell wall adsorption.Infrared spectrum results show that-OH,-NH,-CH3,-CH2,-CH and other groups participate in the adsorption of CY by RS60;-OH,-NH,-CH3,-CH2-CH,-CO and other groups participate in the adsorption of CY by D15.Combined the reaults of SEM and different cellular components adsorption,the mechanisms of strain RS60 and D15 might include surface adsorption and diffusion.Heat,acid,alkali and proteinase K promoted the CY adsorption capacity of YS81 and HP.Snail enzyme had no significant effect on the adsorption rate.The extracellular polysaccharides of the two yeast strains did not participate in the adsorption.After removing the extracellular polysaccharides,more adsorption sites were exposed and the adsorption rate increased.The adsorption of CY by strains YS81 and HP was mainly based on the cell wall,and the protoplast was complementary.Infrared spectra showed that the functional groups that participate in the adsorption of CY by YS81 including OH,NH,-COOH,and-P=O;the functional groups that HP adsorbs CY including hydroxyl,amino,carboxyl,amide,and phosphate groups.The mechanisms of strain RS60 and D15 might include surface adsorption and diffusion.?4?Preliminary application of CY adsorbing probiotics.The four strains inactived by high temperature could be used for the removal of CY from fruit and vegetable juices.The cypermethrin removal effect is good,and there is no obvious effect on pH,solids,total acid,color difference and other indicators,and there is a good application prospect.In this study,4 strains with high CY adsorption capacity were screened to study their adsorption characteristics.The mechanism was explored from different perspectives and used as an adsorbent for the removal of CY from fruit and vegetable juices.For the removal of CY in food or human body,it provides bacterial resources,theoretical basis and data reference. |
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