Effects Of Irradiation On The Migration Of Nanometal From Nanometal Composite Films To Food/Food Simulant

Application of nanometal materials in food packaging can improve the mechanical and barrier properties of the packaging,and exhibit good antimicrobial activity for longer shelf life of foods.As a popular non-thermal sterilization technique,irradiation could produce desired food preservation effects without significantly affecting food attributes compared with the traditional thermal sterilization techniques.The utilization of metallic nanoparticles and irradiation are both effective approaches for preventing food spoilage and these two approaches exhibit their own features in the aspect of antimicrobial activity.The combination of the two sterilization techniques is an effective way toward better and longer food preservation.In this study,three kinds of nanometal were selected to produce eight nanometal composite films.The effects of irradiation on nanometal in three food simulants under three irradiation conditions were studied.The effects of irradiation on the migration of nanometal under two irradiation types and different polymer matrix were compared.And the migration of nano copper and nano zinc oxide into real foods were studied on the basis of our previous study.The specific studies are listed as follows:(1)Eight nanometal composite films were prepared by melting blending three nanometals with LDPE and PP,and then converting to films by a casting method.The initial content and thickness of nanometal in nanocomposite films were measured.(2)Three nanometal composite films(Cu-LDPE-1,Zn O-LDPE-1,Ag-LDPE-1)were treated under three different Gamma irradiation(10 k Gy)condition(no irradiation,Gamma irradiation without solvent contact,Gamma irradiation with solvent contact).The 20 d of migration concentration of nanometal in three food simulants(pure water,95% ethanol,3% acetic acid)was determined by ICP-MS.According to the migration results,we designed a verification experiment by using XPS to investigated the effect of irradiation on the oxidation of nano silver.TEM was used to characterize the micro morphology and dispersion of nanometal in the nanocomposite films,and the thermal and barrier properties of the nanometal composite films before and after irradiation were characterized.The results showed that: firstly,the maximum migration of nano copper,nano zinc oxide and nano silver in 3% acetic acid were higher than that in pure water and 95% ethanol.Secondly,in 95% ethanol,the migration of nano copper and nano zinc oxide of the solvent contact irradiation group were 19 and 3 times than that in the control group,and the migration of the two nanometal in ethanol follows the following regulation: irradiation with solvent contact >irradiation without solvent contact >no irradiation.Finally,in the migration of nano silver,the release of nano silver in the three food simulants follows the same regulation “solvent contact >irradiation without solvent contact >no irradiation”.Therefore,the effects of irradiation on the release of nanometal is related to the type of nanometals,the type of food simulants and irradiation conditions.XPS results that there exist oxidation effects of irradiation on nano silver,which confirms that irradiation oxidized nanometal to promote metal dissolution.(3)On the basis of the previous research,the factors(eg.irradiation type,polymer matrix)related to the effects of irradiation on the migration of nanometals were further studied.Gamma and electron beam irradiation were used in this study.Ag-LDPE-1 and Ag-PP-1 films were selected to conducted the migration test.The results showed that under room temperature,the migration of the nano silver in Ag-LDPE-1 was larger than that of Ag-PP-1 in the same irradiation condition.Secondly,the effects of Gamma irradiation and electron beam on the migration of nano silver was related to the food simulants.In the release to water and 3% acetic acid,the highest migration amount appears in the group of electron beam solvent-contact irradiation while in 95% ethanol,Gamma solvent contact irradiation had the greatest effects on the migration of nano silver(both in Ag-LDPE-1 and Ag-PP-1).It is confirmed that the effect of irradiation on the migration of nanometal was related to the type of irradiation,the type of polymer and food simulants.(4)The migration of nano copper and nano zinc oxide from Cu/LDPE and Zn O/LDPE nanocomposite films into pure milk and yoghurt was studied under ambient temperature of 70 ? for 2 h,and compared with the migration of nanometals in the corresponding food simulants of pure milk and yoghurt.The migration of nanometals from UV-treated nanocomposite films to milk products and the migration of nanometals under the cooking conditions were detected.The results showed that both the migration of nano copper and nano zinc oxide in yoghurt(Cu: 49.91?171.57 ?g/kg,Zn O: 224.99?711.05 ?g/kg)was significantly higher(P<0.05)than that in pure milk(Cu: 46.32?64.21 ?g/kg,Zn O:136.54?239.61 ?g/kg).Significant differences exist between the migration of nano copper and nano zinc oxide in milk products and its corresponding food simulants.Therefore,the current standards for selecting food simulant of pure milk and yoghurt were not suitable for nano copper and nano zinc oxide.UV treatment had no effects on the nanocomposite films because whether the films were treated with UV or not,the migration of the nano copper and nano zinc oxide in the milk products showed no significant difference(P>0.05).For the release of nano copper and nano zinc oxide under the cooking condition,the maximum migration of copper and zinc oxide were 23.63?60.35 ?g/kg and 100.21?233.86 ?g/kg,which were far lower than the special migration limits(SML)recommend in the regulation(5 mg/kg).