| Alternaria can cause grapes to rot during transportation and storage under suitable conditions,moreover,which could produce alternariol(AOH)and alternariol monomethyl ether(AME)and endanger human health.At present,silicate minerals have been used to remove mycotoxins.Sepiolite,the characteristic mineral resource in Xiangtan,is one type of silicate minerals,which is non-toxic and tasteless and has advantages of high specific surface area,porous structure,rich adsorption sites.However,most research applied sepiolite to adsorp heavy metal ions and dyes in wastewater,and the use of sepiolite to remove mycotoxins is rare.In this study,the adsorption effects of sepiolite on Alternaria toxins AOH and AME under different conditions were explored in order to provide a new way for the removal of mycotoxin and the new application of sepiolite.The main results are as follows:(1)The effects of solution pH,adsorption time,initial concentration and adsorbent dosage on the adsorption of AOH and AME by sepiolite were evaluated by single factor experiment.The optimum adsorption conditions were as follows: pH=4.0,the adsorbent dosage was 2 g/L,the initial concentration was 5 μg/mL,the adsorption equilibrium time was 120 min.and the AOH adsorption rate can reach 82.33% in this condition.The optimum adsorption conditions were: pH=4.0,the adsorbent dosage was 2 g/L,the initial concentration was 5 μg/mL,the adsorption equilibrium time was 90 min,and the AME adsorption rate was 93.78%.BET,FT-IR,and XRD results showed that the crystal structure of sepiolite did not change after adsorption,suggesting that the toxin might be adsorbed on the surface of sepiolite or entered the pores of sepiolite.The kinetic and thermodynamic analyses demonstrated that the adsorption of AOH and AME by sepiolite was more consistent with the Langmuir adsorption isotherm model and the pseudo-second-order kinetics model,indicating that the adsorption process of sepiolite to AOH and AME was similar,mainly for monolayer adsorption.Moreover,these adsorption processes have chemical actions such as electrostatic attraction and ion exchange,revealing that these adsorptions were the result of the joint action of physical adsorption and chemical adsorption.The thermodynamic parameter △G of the adsorption processes are all negative,indicating that the processes of adsorption of AOH and AME by sepiolite is a spontaneous exothermic process,which does not require additional energy from the outside.(2)The effects of solution pH,adsorption time,initial concentration and adsorbent dosage on the adsorption of mycotoxin by sepiolite were investigated by single factor experiments in buffer solution system and grape juice.The optimal adsorption conditions in buffer system were determined.It is: pH=4.0,adsorbent dosage=2 g/L,the initial concentration=5 μg/mL,the adsorption equilibrium time=90 min,and the adsorption rates of AOH and AME can reach 55.53% and 82.73%,respectively,under this condition;The optimum adsorption conditions for grape juice are: natural pH of grape juice,adsorbent dosage=5 g/L,the initial concentration=2 μg/mL,the adsorption equilibrium time=60 min,and the adsorption rates of AOH and AME can be respectively reached 38.43% and 75.42% under this condition.The effect of solution pH and sepiolite dosage on the adsorption effect is similar to that of the unit system,while the adsorption time and adsorption amount are lower than the unit system.Among them,the decrease of AOH adsorption rate is particularly noticeable,indicating that there is an adsorption competition between AOH and AME,and the affinity of AME to sepiolite is greater than AOH.Additionally,the non-selective adsorption of sepiolite lead to the adsorption of more impurities the in complex medium such as grape juice,resulting in a decrease in the adsorption amount of the adsorbed target.The adsorption processes of AOH and AME mixture by sepiolite in buffer solution and grape juice were more consistent with Langmuir adsorption isotherm model and quasi-secondary reaction kinetics model,similar to unit system adsorption.Besides,this adsorption process did not affect the pH,soluble solids and titratable acid content of the grape juice.In summary,this study revealed the adsorption mechanism of sepiolite adsorbing Alternaria toxin AOH and AME,and explored the application of sepiolite in grape juice,supporting a better theoretical on sepiolite resources application and the removal of Alternaria toxins in grape juice. |
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