Study On Migration Of Caprolactam In Curdlan-based Packaging Film And Infrared Spectroscopy Detection

Caprolactam（CPL）is a common additive in food packaging materials,which can improve the mechanical properties of packaging,and is commonly used in actual production.The standard of adding quantity of CPL is unlimited at home and abroad,but the migration limit in food is 15 mg/kg.Excessive CPL will migrate to food,even exceed the migration limit,thus endangering human health.Therefore,it is very important to analyze and detect CPL in food and packaging.Near infrared（NIR）and mid infrared（MIR）spectroscopy technology is a non-destructive detection method which can be used in the analysis and detection of food and food packaging.It has the advantages of fast analysis speed,no pretreatment,good reproducibility of results,and environmental friendliness.In order to investigate the effect of CPL on the performance of bio-based food packaging film and its migration in food simulants,a new method for rapid and non-destructive analysis of CPL content in food packaging film and sauces was established.Supported by the project of"research and development of new food packaging materials and key equipment for intelligent packaging"（2018YFd0400703）of the national key R&D plan,a series of curdlan-based films containing different concentrations of CPL were prepared,and the effects of CPL content on the mechanical properties and barrier properties of the films were studied.The migration models of CPL in food simulants were established.Quantitative analysis models of CPL in curdlan-based film and sauces（ketchup,salad dressing and blueberry jam）were established based on NIR and MIR spectroscopy technology and three data fusion strategies.The research contents and results were as follows:1.The relationship between the CPL content and the packaging properties of curdlan-based filmA series of curdlan-based food packaging films with different CPL content were prepared.The packaging performances of the films were tested,and the micro-structure of the surface and cross-section of the film was analyzed.The results show that an appropriate amount of CPL improves the tensile strength and elongation at break of the film and reduces its transparency,water absorption and water vapor permeability by improving the micro-structure and the density of the film structure of the films.However,the addition of CPL will also reduce the glass transition temperature（T_g）,melting temperature（T_m）and endothermic enthalpy（ΔH）of the melting process,but has no obvious effect on the crystallization temperature（T_c）.This means that an appropriate amount of CPL can improve the mechanical properties of packaging materials,improve light-proof performance,enhance barrier properties,and at the same time make the heat resistance of the film worse.Therefore,according to a series of performance parameters and micro-structure changes of curdlan-based films with different CPL content,combined with the actual production cost,packaging safety and other factors,the optimal addition amount of CPL in food packaging materials was proposed as 5%.2.Migration law and migration model of CPL in food simulantsThe migration law and influencing factors of CPL with initial concentrations of1%,2%,3%and 5%in food simulants at 25℃,40℃and 60℃were studied by migration test.The Weibull migration model of CPL in food simulants with C∞,τandβwas established by using migration data,and the external validation of the model was carried out.The results show that the higher the temperature,the faster the initial migration rate,the higher the amount of migration at the same time,and the shorter the time to reach the equilibrium state of migration;in a certain range of time,the amount of migration gradually increases with the extension of time,and when it reaches the equilibrium state of migration,the amount of migration no longer changes with time,and basically remains at the level of the maximum amount of migration;The higher the initial concentration,the higher the maximum migration;the migration of CPL in the four food simulants from high to low is:4%acetic acid,distilled water,50%ethanol,n-hexane.Weibull migration model predicted accurately and can be applied to predict the migration of bio-based packaging film contacted with sauses.3.Determination of CPL content in curdlan-based film based on infrared spectroscopyThe PLS and SVM prediction models of the CPL content in curdlan films under9 spectral pretreatment methods were established based on NIR,MIR,and NIR-MIR fusion spectroscopy technology and chemometric methods.By comparing the evaluation parameters of the models,the optimal quantitative analysis model of CPL content in films was determined.The results show that the optimal model of NIR-SNV-SVM has R_p² of 0.9552,RMSEP of 1.251%and RPD of 4.50;the optimal model of MIR-1^st-SVM has R_p² of 0.9092,RMSEP of 1.614%and RPD of 3.38.This shows that the prediction effect of low-level and high-level fusion model is better than that of single NIR and MIR model,while the prediction effect of mid-level fusion model is slightly worse.The high-level fusion model has the best prediction effect among them with R_p² of 0.9606,RMSEP of 1.211%and RPD of 4.52.Therefore,this study provided a new method based on NIR-MIR spectral high-level fusion technology to detect the CPL content in curdlan films,which has the advantages of fast analysis speed,no damage to samples,green environmental protection and low cost.4.Determination of CPL in sauces based on infrared spectroscopyBased on NIR,MIR and NIR-MIR fusion spectroscopy,combined with nine spectral pretreatment methods and chemometric methods,the quantitative analysis models of CPL in ketchup,salad dressing and blueberry jam were established respectively.By comparing the evaluation parameters of the models,the optimal quantitative analysis model of CPL in sauces was determined.The results show that for ketchup,salad dressing and blueberry jam,the prediction effect of high-level fusion model is better than that of low-level fusion model,mid-level fusion model,single NIR model and MIR model.The R_p² of high-level fusion model for ketchup,salad dressing and blueberry jam were 0.9990,0.9929 and 0.9989,respectively;RMSEP were 1.079 mg/kg,2.930 mg/kg and 1.151 mg/kg,respectively;RPD were32.12,11.78 and 30.17,respectively.The models all have good prediction ability for CPL content.In order to further verify the applicability of NIR-MIR high-level fusion model in detecting a variety of sauces,NIR and Mir spectra of ketchup,salad dressing and blueberry jam were integrated to establish a high-level fusion prediction model based on CPL content in three sauce substrates,with R_p² of 0.9961,RMSEP of 2.151 mg/kg and RPD of 15.91.The results show that NIR and MIR spectroscopy combined with high-level data fusion method can provide a new method for non-destructive and rapid quantitative analysis of organic hazards in sauces,which has the advantages of accurate results,good reproducibility and environmental friendliness.