The Method And Mechanism Of Biosorption Of Forchlorfenuron In Kiwifruit Juice By Inactivated Yeast

Forchlorfenuron is a relatively new phenylurea plant growth regulator.The effect of this synthetic cytokinins is to promote cell division and cell enlargement.Therefore,it has been used extensively to increase the productivity and quality in kiwifruits.In last few years,the presence of residues and their safety in kiwifruits have increasingly caused concern,which was resulted in the abuse of forchlorfenuron due to pursuing economic benefits.In addition,considering its toxicity and possible health risks to consumers,it is an urgent need for industry to seek a safe and effective removal method currently.Ten yeast strains were investigated to obtain the most efficiency strain on forchlorfenuron biosorption.The effect of different factors,including yeast dosage,initial concentration of forchlorfenuron,biosorption time,pH and biosorption temperature,on biosorption rate were assayed.In addition,the biosorption conditions were optimized and kinetics models and thermodynamic model were proposed.After that,the biosorption mechanism of forchlorfenuron from kiwifruit juice by heat-inactivated yeast was investigated.The main results of the study were as follows:(1)The most efficiency yeast strain(SC5)was selected to further study by comparing the biomass,forchlorfenuron adsorption rate as well as impact on kiwifruit juice quality of different strains.(2)The effect of yeast dosage,initial concentration of forchlorfenuron,biosorption temperature,pH,and biosorption time on forchlorfenuron biosorption were investigated.Firstly,the biosorption rate increased gradually as the yeast dosage increased,and there was very little change when yeast dosage up to 32 mg/mL.Secondly,the biosorption rate increased at early stage and then decreased,and reached equilibrium finally.Thirdly,a reduction was noted in the biosorption rate at increased initial concentration of forchlorfenuron and temperature.Finally,the biosorption capacity was increased by increasing pH value,and reached a maximum value when pH 5.0.The optimum adsorption conditions were as follows: inactivated yeast dosage,28 mg/mL;initial forchlorfenuron concentration,0.2 ?g/mL;and adsorption time,3 h.(3)Kinetics curves of biosorption of forchlorfenuron were obtained at differenttemperatures by inactivated yeast biomass.It was observed that the biosorption capacity increased at early stage and then decreased,and reached equilibrium finally.Additionally,the biosorption kinetics was best described by the pseudo-second-order model and the equilibrium data fitted well with the Freundlich model when the forchlorfenuron concentration ranging from 0.5 to 10 ?g/m L.It was also found that the biosorption was spontaneous,exothermic and with the decrease of entropy.(4)Biosorption of forchlorfenuron by different parts of heat-inactivated yeast was investigated,but it can't be inferred which part played a leading role in binding process yet.Considering the cell wall was first contacted during the forchlorfenuron biosorption,so it was selected to further study of mechanism.Then which components of cell walls were participated in the biosorption was studied,and the results revealed that the protein components was essential in binding and the lipids were unlikely involved.Binding ability and characterization of heat-inactivated yeast by chemical modification were carried out,and the results suggested that functional groups,including amino,hydroxyl and carboxyl,presented in the cell walls were mainly responsible for forchlorfenuron binding to inactivated yeast.And the concentration of these functional groups were very critical.Moreover,hydrogen bonding and hydrophobic interaction were also involved.Stability of the yeast-forchlorfenuron complex was assessed by desorption studies.It was observed that both irreversible adsorption and reversible adsorption were included in the biosorption process.