| With the frequent appearances of food safety problems in China, food quality and safety had drawn great attention of researchers. Food packaging safety is one of the most important parts in food safety. Most pollution of food packaging materials results from the uses of inferior packaging materials and raw materials during manufacturing process. Food is a complex matrix including sugar, acid, salt and oil which could contact with the packaging container. The interactions of the food ingredients and the packaging container will cause the physical and chemical changes of the packaging materials. These reactions result in the migrations of harmful substances from the packaging materials to the food and thus the food is polluted.Plastic, as a kind of synthetic polymers, is one of the fastest growing food packaging materials recently. Polycarbonate (PC) plastic is widely used in the production of plate, kitchen supplies, coffeemaker, filter, baby bottles and water bottles and so on because of its characteristics such as toughness, high transparency and heat resistance. Bisphenol A (BPA) is an important monomer compound for PC synthesis, but BPA can migrate from PC plastic to the food materials and may play harmful effect on human health. In the present research, the BPA was selected as the main research target and its migration from PC plastic to food materials was investigated by liquid chromatography-fluorescence detection. The effects of different external conditions including temperature, time and heating methods on the migration features of BPA from the PC plastic to acid, sugar and water at different pH and hardness were investigated. The surface morphology of the plastic was observed by atomic force microscopy to further illuminate the microscopic characteristics of the migration of BPA in PC materials. The results showed that:(1) The PC buckets and PC baby bottles were dissolved by dichloromethane and the dissolved chemical substances were detected by gas chromatograph-mass spectrometer. The main pollutants in the PC plastics are alkanes, esters and phenolic substances and the phenolic substances displayed the highest BPA concentration. The BPA concentrations in the market PC samples ranged from3.24to9.10mg/kg as detected by high performance liquid chromatography-fluorescence. It is revealed that PC containers are commonly polluted by BPA.(2) The migration amounts of BPA from PC plastics to distilled water and different concentrations of ethanol solutions (15%,65%and95%) were detected to explore its migration features in the alcohols. The results showed that the migration of BPA in ethanol was affected by ethanol concentrations, temperature and time. The migration amounts in different concentrations ethanol were95%ethanol>65%ethanol>15%ethanol> distilled water. In the same ethanol concentration, the migration amounts of BPA increased with the contact temperature increased form20℃to75℃. The diffusion coefficient increased with the increasing temperature and ethanol concentration. The diffusion coefficient value measured in the present experiment is higher than the predicted value by the general diffusion coefficient model.(3) The effects of pH and heating methods on the migration process of BPA were investigated. The pH of the water was regulated by glacial acetic acid, NaOH, citric acid-sodium citrate. The migration amount of BPA significantly increased above pH7(P<0.05). It is revealed that the alkaline conditions are favorable for the migration of BPA in PC materials. The observations with atomic force microscopy showed that the plastic surface became rougher after soaked by alkali solution. The surface layer is exposed which make bisphenol A easier to dissolution. There is a significant difference in the migration of BPA in tap water, mineral water and distilled water in the microwave heating process (P>0.05). In the constant temperature heating process, there is no significant difference in migration of BPA (P>0.05) between mineral water and tap water. The equilibrium time of the migration by the microwave heating was shortened nearly12times than that by constant temperature heating.(4) The migration of BPA from PC materials to the salt, sugar and acid solutions at different temperature were investigated. The results showed that the migration of BPA in two valent salt solution was higher than that in the monovalent salt solution. In the two valent salt solution, the migration of BPA was higher in Ca+salt than that in Mg+salt. In the monovalent salt solution, the migration of BPA was higher in Na+salt than that in K+salt. When the NaCl and KCl concentrations were higher than0.1%, the migration amount of BPA in NaCl and KCl solutions were significantly different from that in distilled water (P<0.05). When the CaCl2and MgCl2concentrations were0.01%, the migration amount of BPA in CaCl2and MgCl2solutions were significantly different from that in distilled water (P<0.05). The0.1%-9.0%concentrations of acetic acid, citric acid, tartaric acid, malic acid and lactic acid were selected as acid food simulants. Different types of acids showed different effects on the migration amount of BPA. There is a significant difference of the BPA migration amount between the0.1%acid soaking solution and distilled water (P<0.05). With the increasing concentrations of sucrose, glucose, lactose and xylitol, the migration amount of BPA increased. The migration amounts of BPA in1%lactose,2%glucose,2%sucrose,1%xylitol were significant different from that in distilled water (.P<0.05) and the xylitol solution showed the highest migration amount of BPA.(5) The effect of temperature and time on the migration amount of BPA in the PC containers containing tea and reconstituted food were investigated. When the same kind of tea at1.25%,2%,5%concentrations were heated at95℃for1h, the BPA amount displayed significant differences at different concentrations of tea (P<0.05). Different types of tea played different roles on the migration of BPA. When the tea level was1.25%, there is no significant difference among different types of tea (P>0.05). When the tea concentration increased to2%, the BPA amount were significantly different among different types of tea (P<0.05). At high concentration (5%), the migration amount of BPA in Tie Guan Yin was the highest, and the jasmine tea showed the least migration amount of BPA. There is no significant difference between the Mao Feng and black tea (P>0.05). Different temperature and food types resulted in different migration amount of BPA. The migration of BPA in different food is in the range of3.44-41.74μg/kg, in which coffee and milk powder showed higher migration amount of BPA. |
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