Construction And Fish Preservation Of Chitosan Films Doped With Proanthocyanidins-loaded Nanoparticles

Food packaging helps to regulate food and its surrounding conditions,reduce corruption and deterioration in the process of storage and circulation,and plays a vital role in food quality control and safety assurance.Compared with non-degradable synthetic polymer packaging materials,bioactive films prepared from natural biopolymers show great potential in food packaging applications.Among them,chitosan is a natural polysaccharide whose content is second only to cellulose.It has the advantages of rich sources,good film-forming,high biocompatibility and biodegradability,which has great application potential in food packaging.However,the films prepared by single chitosan（CH）have some defects,such as poor antioxidant,mechanical and barrier properties.Directly blending CH and active substances is easy to be affected by environmental conditions,resulting in the decline of their activity.In this paper,chitosan/chondroitin sulfate（CH/CS）nanoparticles（NPs）loaded with proanthocyanidins（PC）were prepared for the first time and blended with CH solution to prepare chitosan-nanoparticles（CH-NPs）composite film with excellent performance,which was used for the preservation of refrigerated grass carp fillets.The specific research contents are as follows:Firstly,PC was encapsulated by CH/CS system,and ultrasonic treatment was introduced to prepare CH/CS-PC NPs.Ultrasonic treatment broke the complex into NPs through acoustic cavitation effect,inducing the formation of amide bond and promoted the cross-linking of CH and CS.The particle size of NPs was the smallest when the ultrasonic duration was 1 min.The preparation parameters such as CH/CS mass ratio,total CH/CS concentration,PC concentration,and p H affected the particle size,Zeta-potential,entrapment efficiency and loading capacity of NPs by regulating the charge,ionization degree and binding site of polyelectrolyte.The prepared CH/CS-PC NPs had a particle size of 293 nm,a Zeta-potential of-21.8 m V,a PC encapsulation efficiency of 37.5%,and a loading capacity of 11.1%（1:3 of CH/CS mass ratio,1.5 mg/m L of total CH/CS concentration,0.5 mg/m L of PC concentration,and 3.25 of p H）.By observing the micro morphology of PC-loaded and blank NPs,it was found that the addition of PC would lead to the shape distortion and aggregation of NPs,and increased the particle size.Compared with free-PC solution,NPs suspension loaded with PC showed higher free radical scavenging rate after storage under illumination conditions,indicating that CH/CS structure has a protective effect on PC activity.The NPs suspension was mixed with CH solution,and the CH-NPs composite film was prepared using the tape casting method.The effect of the addition ratio of NPs（4%,8%,12%,and 16%）on the performance of the composite film was investigated.CH/CS-PC NPs were dispersed and embedded in CH film matrix due to the good compatibility.With the increase of the addition ratio,the surface roughness of the film increased,and the antioxidability and UV-vis light barrier ability increased.Zeta-potential measurement,FTIR,and rheological tests showed that there were hydrogen bonds and electrostatic interactions between NPs and CH film matrix.The cross-sectional morphology and SAXS analysis of the film showed that the addition of NPs reduced the size of CH aggregates in the film matrix and made the composite film structure more compact.Therefore,CH-NPs composite film showed stronger mechanical properties and water vapor and oxygen barrier properties than pure CH film.The tensile strength of NPs-16%film was 88.4%higher than that of CH film,and the elongation at break,water vapor permeability,and oxygen permeability were 24.4%,22.7%,and 34.7%lower than those of the control group,respectively.The addition of NPs further enhanced the antibacterial performance of CH film and effectively inhibited Staphylococcus aureus,Escherichia coli and fish spoilage bacteria（Pseudomonas aeruginosa and Aeromonas hydrophila）.In addition,the encapsulation effect of CH/CS on PC slowed down the damage of environment to the antioxidant activity of PC.The free radical scavenging rate of CH-NPs film was 7.1%-94.3%higher than that of CH and PC blend film after UV/thermal treatment for 1 h-2 h.Finally,CH-NPs（NPs-16%）composite film was used to pack the fish fillets,which was used for the preservation of refrigerated grass carp fillets.The effects of PE film,CH film and CH-NPs film on the quality of fish were explored.The results showed that CH-NPs film had no adverse effect on the color and p H of fish.CH-NPs composite film had higher surface roughness,reduced the contact area between the film and the fish fillet,and had no adhesion and damage after 8 d storage,showing better packaging characteristics than CH film.The physical and chemical indexes such as texture,TBARS,total sulfhydryl content,TVB-N,biogenic amine and microbial analysis of fish fillets packed with CH film and CH-NPs film were better than those of the control group.CH-NPs film could better inhibit microbial growth and fat and protein oxidation due to its stronger antioxidant,antibacterial,and oxygen barrier properties.After 8 d storage,the TBARS value and sulfhydryl oxidized content of fish in CH-NPs group were 51.1%and 38.0%lower than those in the control group,respectively,and the total viable counts were 2.24 log₁₀ CFU/g lower than the control.CH-NPs film has the potential to be used as active packaging for fresh fishery product preservation.