Research On The Preparation And Antioxidant Characteristics Of Tea Polyphenol-chitosan Nanoparticle Gelatin Composite Films

As the concerns of people on environmental problems increase,the development of edible films based on renewable and biodegradable environment-friendly natural biopolymers to substitute traditional synthetic plastic packaging films has been the current research focus in the field of food packaging.However,edible films generally show poorer mechanical strength and water vapor barrier properties than those of plastic polymer films due to their own physical and chemical properties.Moreover,the protective effects of pure edible films on food are limited.These all limit their industrial uses.In this study,gelatin was used for the formation of edible films.The influences of chitosan-sodium tripolyphosphate(CS-TPP)and chitosan hydrochloride-sulfobutyl ether-β-cyclodextrin(CSH-SBE-β-CD)nanoparticles on the mechanical and barrier properties of gelatin films were firstly studied.The CSH-SBE-β-CD nanoparticles(CSNs)were selected to encapsulate tea polyphenol(TP).The influences of formulation parameters on the encapsulation efficiency and properties of CSNs,as well as the pH and temperature stability of CSNs were then analyzed.Finally,gelatin films incorporated with TP-CSNs were prepared to study their antioxidant activities in real oil system.CS-TPP nanoparticles and CSNs,with similar particle sizes(around 150 nm),were firstly prepared by ionic cross-linking.With the addition of CSNs,the gelatin films had a maximum 18% increase in tensile strength,a maximum 20% decrease in elongation at break and a maximum 10% decrease in water vapor permeability.However,the gelatin films with CS-TPP nanoparticles had a maximum 40% decrease in tensile strength,a maximum 300% increase in elongation at break and a maximum 45% increase in water vapor permeability.The tensile strength of gelatin films decreased and the elongation at break increased as the content of Na OAc increased from 0 to 12.25%.The dynamic mechanical thermal analysis suggested that the presence of NaOAc promoted the mobility of gelatin chains and decreased the glass transition temperature from.Combing with the isothermal water absorption analysis,NaOAc could act as a plasticizer through absorbing moisture and disturbing the interactions between gelatin chains.The decrease in tensile strength and the increase in elongation at break of films with CS-TPP nanoparticles might be caused by the formation of NaOAc when using NaOH to adjust the pH of CS solution.The CSNs,which improved the mechanical and barrier properties,were used to encapsulate TP.The particle sizes and the encapsulation efficienies of TP-loaded CSNs(TP-CSNs)increased with decreasing CSH/SBE-β-CD mass ratios from 1.2/1 to 0.75/1.Atomic force microscopy images showed that TP-loaded CSNs were regular spherical in shape.Cross-linking between CSH and SBE-β-CD was demonstrated with FTIR analysis,and TP was mainly located in the core of CSNs.Epigallocatechin gallate(EGCG)were used as a model guest molecule to study the encapsulation mechanism.The stoichiometry of EGCG-SBE-β-CD inclusion complexes(EGCG-ICs)was determined to be 1:1,based on the Job’s method.The formation of inclusion complexes was further confirmed by the fluorescence and NMR spectroscopy,and A-ring of EGCG might be included.Therefore,inclusion complexes of TP and SBE-β-CD were initially prepared and then cross-linked with CSH for TP-CSNs formation.Also,the particle sizes increased with increasing CSH concentrations.The encapsulation efficiencies increased with increasing CSH concentrations while decreased significantly with increasing TP concentrations.The pH range(2-7.5)and temperature range(25-55 °C)which was commonly used during film-forming process were selected to investigate the stability of TP-CSNs.EGCG,the main component in TP,was also used to prepare EGCG-loaded CSNs(EGCG-CSNs).The particle sizes of EGCG-CSNs were unchanged in the pH range of 3 to 5,but disaggregation occurred in pH < 3 and aggregation happened in pH > 5.The microenvironment of EGCG-ICs appeared to be intact in the p H range of 4 to 6.5,disaggregation happened beyond this range.However,the in vitro antioxidant activities(DPPH radical scavenging activity,ferric reducing power)of EGCG-CSNs,EGCG-ICs and EGCG could be maintained when pH < 5.When pH was above 5,the in vitro antioxidant activities of EGCG-CSNs were lower than those of EGCG-ICs and EGCG due to the aggregation of EGCG-CSNs.The particle sizes of EGCG-CSNs were increased and the microenvironments of EGCG-ICs were gradually affected as storage time(0-24 h)increased at any temperature,which were further affected as temperature increased from 25 to 55 °C.The decrease in antioxidant activities of EGCG-ICs and free EGCG with increasing storage time and temperature were modest compared to the prominent decreases in antioxidant activities of EGCG-loaded CSNs.The extreme entrapment of EGCG-ICs and/or free EGCG in the aggregated CSNs restricted the release of EGCG,thus inhibiting the antioxidant activities.According to the previous results,gelatin films incorporated with TP-CSNs with three different encapsulation efficiencies(~50%,~80%,~100%)and particle sizes(140,170,240 nm)were prepared by three different CSH concentrations(0.5,1,2 mg/mL).The mechanical strength and barrier properties were enhanced with increasing encapsulation efficiencyies and particle sizes.The stability of TP-loaded nanoparticles was maintained during the film drying process from the analysis of free TP content in the redissolved film solutions.Nanoparticles appeared to be homogeneously dispersed within the film matrix by microstructure analysis.Composite films showed no significant difference in visual aspects,while the light transmittances(250-550 nm)were decreased with incorporation of TP.TP-loaded films had ferric reducing and DPPH radical scavenging power that corresponded to the EEs.Sunflower oil packaged in bags made of gelatin films embedded with nanoparticles of 80% EE showed the best oxidation inhibitory effect,followed by 100% EE,50% EE,and free TP,over 6 weeks of storage.However,when the gelatin films were placed over the headspace and were not in contact with the oil,the free TP showed the best effect.The controlled-release tests in 95% ethanol showed that the free TP had the largest release rate followed by 50%,80% and 100% encapsulation efficiency.Also,films maintained their structures in the simulant.These results indicate that the sustained release of TP in the contacting surface can ensure the protective effects,which vary with free/encapsulated mass ratios,thus improving antioxidant activities instead of increasing dosage.