Study On The Residual Contaminants In Paper And Board Food Packaging Materials And Their Migrations

Due to their unique physical and mechanical properties and environmentally benign feature, paper base package materials are importance for food packaging industries. During manufacture and the subsequent treatment processes, chemicals are added as additives and are generated as byproducts. Some of those chemicals are toxic and can migrate into foods. The migration of harmful substances from these package materials to food results in contamination and thus constitutes a great threat toward public health. the safety and health of paper based packaging materials have increasingly drawn attention in the developed nations, and the researches on the contaminations analysis and in theory establishment for contaminant migration became hot topics.This study is on the quantitative and qualitative determinations of volatile organics and alcohol extractives in paper base package materials. Partitioning coefficients of model contaminants between the packaging materials and air were investigated through microsampling and volume ratio method. Desorption kinetics of model organic contaminants and transfer phenomena of model organic contaminants between package materials and food were also studied. The results obtained are as follows:The study on the optimal conditions for solid phase micro extraction (SPME) of volatile organics in paper base packaging materials showed that the optimized extraction condition is follows: 100μm polydimethylsiloxane (PDMS) SPME fiber was placed in the headspace of paper sample at 60℃for 80min, and the adsorbed organics readily desorbed in a gas chromatography injection port and completed in 2 minutes at 270℃.The SPME extracted volatile organics and ethanol extracts of 20 paper base package samples were analyzed by using GC-MS. It was determined that the major volatile organics in the samples include alkane, chloralkane, alkyl phthalates, aldehyde, ester, alcohol and aromatic compound, naphthalene and phenol, and the main components found in the ethanol extracts consist of alkane, chloralkane, alkyl phthalates, amide, aldehyde, ester, ketone, carboxylic acid, aromatic compounds and heterocyclic compounds. The contents of the alkane in the unprinted paper or the deinked handsheet are less than those in printed ones,that indicates the sourses of hydrocarbon is during printing process.Partition coefficients (Kpaper/air) of o-xylene, dodecane, naphthalene, diphenyl oxide and diisobutyl phthalate in cartonboard, kraft and fluting medium were determined by microsampling and the adsorption isotherms of the contaminants were plotted. Results indicated that it was obviously that not only the boiling point of the model compounds, but also the chemical properties and the stereochemistry of the compounds play important role in their Kpaper/air value. Kpaper/air value had a proportional relationship with the grammage and the thickness of paper sample. The lower of the grammage and the thickness, the lower of Kpaper/air value would be. Kpaper/air values of selected model compounds increased in this order: o-xylene, dodecane, naphthalene, diphenyl oxide, diisobutyl phthalate. Kpaper/air decreased with an increasing temperature, which indicated that the comtaminants in paper and board packaging materials is more dangerous to food at high temperature. Based on the theory of indirect headspace gas chromatographic method for vapor-liquid phase equilibrium study, volume ratio method was developed to measure the partition coefficient of organic contaminants between paper base packaging materials and air, Kpaper/air. The derived calculation procedure to determine Kpaper/air is , precision analysis and accuracy of the method was experimental verifiied and mathematical analysed. It was found that the relative standard deviation of 5 repeating determinations was 3.6%. The ratio of peak area and the sample volume had significant effect on the testing result. Comparing to the microsampling procedure, volume ratio method was similar in term of their accuracy. The volume ratio method was further validated with the calculations and tests. It was concluded that the volume ratio method was a fast and convenient procedure; it requires neither sample pretreatment nor the information of organic contaminants prior to the test. Consequently, the method is suitable for the determination of Kpaper/air of organic contaminants.A procedure has been applied to determine the transferring kinetics of model contaminants from paper base packaging materials to air through multiple headspace extraction (MHE-GC). The procedure was applied to study the kinetics of selected contaminants (o-xylene, dodecane, diphenyl oxide, diisobutyl phthalate) desorbing from paper and transferring to air. Results indicated the desorption reaction rate constant increased with an elevated temperature. The boiling point and chemical structure of model contaminants also affects the desorption reaction rate constant. Temperature constitutes a predominant effect on the desorbing kinetics of contaminants. The equilibrium time of desorption decreased with an increasing temperature, and the equilibrium time of model contaminants, o-xylene at 100℃,70℃,40℃, are 1h,4h and≥4h, respectively.Temperature had great effect on the migration of the organic contaminants. In the temperature range studied(25℃,50℃,75℃and 100℃), migration rate increased with an increasing temperature, whereas desorbing equilibrium time decreased with an elevating temperature. The grammage and thickness of the paper samples affected the migration rate. The lower the grammage and thickness, the higher of the migration rate and the easier to reach desorbing equilibrium. Whole milk and Tenax displayed similar results in terms of their adsorbing capacity. Both of them demonstrated high adsorption toward the selected model compounds, although Tenax showed a poorer adsorption under an elevated temperature. This may attribute to the thermal degradation of Tenax. Result thus indicated that Tenax is a very good food model for experimental study under low temperature. As a real food, powder mill posses great adsorption capacity and is stable under elevated temperature. As a result, powder mill is a good candidate for the migration studies.