Migration Of Plasticizer From Zein Films To Food In Simulation Systems

Zein has good film-forming properties,and the addition of plasticizers can effectively improve the mechanical properties of zein films.However,the migration of plasticizers would induce the changes of film properties.Up to now,the effect of the packaged food on plasticizer migration have not been focused.Therefore,on the basis of the previous research about mechanical properties of zein films,glycerol/citric acid and glycerol/polyethylene glycol were selected as composite plasticizers to prepare zein films with good barrier properties,and oil and salt were used as flavor simulant and packed with zein films to investigate the migration of plasticizers and the structure change of proteins during storage.A mathematical model of migration was investigated by accelerating experiment to predict the migration of glycerol during storage.Firstly,the barrier properties of zein films with different plasticizers were studied,and the results showed that the kinds and ratio of plasticizers all had significant effect.The moisture absorption rate,water vapor transmittance,oxygen permeability and oil permeability of the films increased gradually with the increase of glycerol ratio when the film was plasticized with glycerol/citric acid.With the increase of citric acid ratio,the oxygen permeability increased and the oil permeability decreased gradually.The moisture absorption rate and water vapor permeability decreased firstly and then increased,and the lowest value of both was all located at the ratio of 0.2 g/g zein.When the film was plasticized by glycerol/polyethylene glycol,the oxygen permeability increased gradually,and the moisture absorption rate,water vapor permeability and oil permeability of the films increased firstly and then decreased along with the increase of polyethylene glycol ratio,the maximum was located at 0.3 g/g zein.Comparatively,zein films plasticized by glycerol(0.2g/g zein)and citric acid(0.2 g/g zein)(CG films),and plasticized by glycerol(0.15 g/g zein)and polyethylene glycol(0.2 g/g zein)were selected to pack oil and salt to proceed the storage test for 24 weeks(W)at 5℃ and 25℃.Secondly,the change of moisture content and plasticizers migration in zein films during storage were studied,and the results showed that.The moisture content in CG film decreased gradually at first 16 W and in PG film at first 20 W,and then increased gradually during storage.The moisture content of film was affected by storage temperature,and lower moisture content of the film was observed at 25℃ rather then 5℃.The migration amount of plasticizer increased firstly and then tended to equilibrate during storage.The migration of plasticizer from films to salt was greater than it to oil for the same film at same temperature.The glycerol migration from from film to salt and oil all reached equilibrium at 12 W.When stored at 5°C and 25°C,the migration of citric acid from film to oil and salt all reached equilibrium at 16 W.The migration of polyethylene glycol from film to oil all reached equilibrium at 16 W,and the migration from film to salt all reached equilibrium at 12 W under 5°C and 25°C.Thirdly,the changes of protein structure during storage were studied.The results showed that with the increasing of storage time the free sulfhydryl content in the films decreased,and the free sulfhydryl content at 25℃was lower than at 5℃.The hydrophobic interactions and hydrogen bonds decreased gradually.Both films maintained an intact appearance and no leakage of contents.At the first 12 W,the moisture content of the salt had no significant change.At the 24 W,the moisture content of the salt packed with CG films increased 0.10% and 0.27% at 5℃ and 25℃,and the moisture content of the salt packed with PG films increased 0.99% and 0.06%,respectively.The acid value and peroxide value of the oil packed with PG and CG films after 24 W storage were all in line with the national standard.But the acid value and peroxide value of oil packed with PG film were all higher than those of packed with CG film.The acid value and peroxide value of the oil packed with CG film and PG film at 5℃ were all lower than at 25℃.So,CG film is more suitable for the package of high-fat foods,while PG film is more suitable for high-salt powders.Finally,the factors influencing the glycerol migration and a mathematical model of plasticizers migration were investigated.The results of the acceleration experiments showed that the glycerol migration increased rapidly at beginning stage and then tended to reach equilibrium which presented a greater migration rate at the initial stage.Higher storage temperature would induce more glycerol migration and shorter equilibrium time.Hydrophilic material induced greater glycerol migration.Higher glycerol ratio led to more migration,but the migration amount is not proportional to the addition amount.The migration of glycerol was influenced by the interaction between glycerol and other plasticizers.Weibull distribution probability model was fitted to the migration of plasticizers based on the accelerated experiments.The results showed this model can predict the migration of plasticizers from films to oil at different storage time.