| Patulin is a kind of microbial source pollutant which is widely existed in fruit, vegetable and their products. As research continues, the biosynthesis mechanism of patulin has been recognized primarily and more effective methods of controlling the production of patulin at gene level are researched at present.and beganing to try to understand from the level of gene and even control the synthesis of patulin. Current research work shows that patulin may cause acute toxicity, subacute toxicity and chronic toxicity to human. Although the current study still remains at the level of animal and cell experiment, but the potential toxicity to human health of patulin is acknowledged around the world, European countries first established the standard of safety limit for patulin, Other countries such as the United States, China and Japan support the draft maximum level of 50 μg/kg for patulin in foods.Chitosan is a kind of biological alkaline polysaccharide which has stable chemical properties. There are a lot of amino and hydroxyl groups on the molecules of chitosan and this special construction provides good solubility and chemical activity. Therefore it has has extensive value of application in the field of environmental protection, food, medical, chemical and cosmetics. Chitosan powders could be prepared into chitosan beads by reversed phase suspension crosslinking method which can provide excellent adsorption properties. In addition, chitosan beads could be modified to enhance adsorption performance.In this study, chitosan beads was used as basic adsorption material and its adsorption properties of patulin and the absorption mechanism were investigated, which could lay a foundation for next research step about modified chitosan beads adsorption characteristics and adsorption mechanism of patulin.1) Chitosan beads were applied to patulin removal for first time. The maximum adsorption capacity for patulin was 626.4 μg/g at pH 7.0,40℃ for 24 h. It was showed that chitosan beads could remove patulin from aqueous solution effectively. Chitosan powders and its beads were characterized by FTIR, XRD and DSC analysis. It was confirmed that chitosan had been crosslinked and the crosslinked chitosan beads were prepared.2) Chitosan beads were suitable for modification because of its high content of active amino and hydroxyl groups. The method of compounding, grafting and replacing group was used to prepare modified chitosan beads. By comparing the three kinds of modification method, it was showed that modified chitosan beads by modifying group had the most effective adsorption property and safety. The optimization of synthetic process improved the adsorption efficiency of macroporous resins. The adsorption experiment results showed that a small amount of thiourea modified chitosan beads could obtain higher adsorption property under low temperature and pH condition which was more suitable for removing patulin from juice. The results of FTIR and EDS confirmed that thiol groups were connected on chitosan beads.3) In order to get full knowledge of the adsorption process of chitosan beads and thiourea modified chitosan beads for patulin, the adsorption mechanism was researched by thermodynamic and kinetic analyzing. The result showed that the chitosan beads adsorption process of patulin belonged to multilayer adsorption and the adsorption rate was affected by two kinds of reactants, thiourea modified chitosan beads adsorption of patulin belonged to chemical adsorption and the adsorption rate was mainly affected by one kind of reactants. Rate-limiting step of the two kinds of beads adsorption of patulin was liquid film diffusion. The movement speed of patulin outside the beads was slower than that inside. The two kinds of adsorption belonged to spontaneous endothermic adsorption process. Better understanding can be obtained by structural simulation and reaction principle analysis. In this assay a reaction mechanism of thiol and patulin is presented under acidic condition and the modification process was showed by the form of drawing.4) According to the content of organic acids, amino acids, total sugar and aroma components in apple juice before and after the adsorption, the results showed that there was no obvious effect on nutrition and aroma components. The removal rate of 0.1 g thiourea modified chitosan beads were 16.61% and 30.29% under the condition of 25 and 40℃, respectively. But 0.5 g thiourea modified chitosan beads could completely remove patulin in apple juice contained 10 mg/mL patulin at 40℃. Reducing patulin concentration could improve the rate of removal. The effect of dynamic adsorption experiment was more effective, especially at low flow rate. |
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