Construction And Fish Preservation Of Chitosan/Alginate Dialdehyde Trilayer Films Incorporated With Cinnamaldehyde And Tea Polyphenol

The primary purpose of food packaging is to maintain food quality,ensure food safety,and expand the shelf life of food against microbial,physical,and chemical hazards during storage and transport,thus it displays a critical role in the food industry.However,traditional petroleum-based plastic packaging materials are single-functional,non-renewable,and non-biodegradable,resulting in constrained application,resource consumption,and environmental deterioration.At present,natural biopolymers such as polysaccharides,proteins,and lipids,have the potential to substitute traditional plastic packaging materials and attracted much attention.Among them,chitosan has been developed as a food packaging material owing to its good film-forming,biodegradability,and biological properties,and its preservation application in fruit,vegetables,aquatic products,livestock,and poultry products is studied.Yet,pure chitosan film has some disadvantages,such as insufficient mechanical properties,barrier ability,water resistance,antibacterial and antioxidant activities,which limits its applicability.Crosslinking modification and multilayer composite films can enhance the physicochemical properties and biological activities of the film,improve its practical applicability,and inhibit oxidation of the food and retard the development of rancidity.Therefore,chitosan and alginate dialdehyde were used as film-forming matrix,cinnamaldehyde and tea polyphenol were used as functional components.The purpose of this study was to construct the thermally-crosslinked chitosan/alginate dialdehyde-cinnamaldehyde/chitosan-tea polyphenol trilayer composite films（CMR/ADA-CA/CS-TP）with good physicochemical,antibacterial and antioxidant properties though thermally-induced crosslinking and layer-by-layer casting method,and to evaluate the preservation of grass carp fillets.It is expected to provide new ideas for seeking alternatives to plastic packaging and provide technical support for solving the bottleneck of fresh aquatic products.The main contents and conclusions are as follows:At first,the influence of the different thermally-induced crosslinking temperatures（25℃,90℃,100℃,110℃,120℃and 130℃）on the microstructure,mechanical properties,barrier ability,and water resistance of pure chitosan film was explored.Tracing the consumption of-NH₃⁺by Fourier transform infrared spectroscopy（FTIR）revealed that CS molecules of the heat-treated films were self-crosslinked through the Maillard reaction.X-ray diffraction（XRD）and scanning electron microscope（SEM）analysis showed that the crystalline structure of the CMR films was reintegrated,and film microstructure was more compact.With the increase in the temperature,the color of the CMR films gradually darkened,resulting in the gradual increase of the browning index（BI）.Compared with the control film（C25）treated at 25℃,the BI of CMR film（C110）treated at 110℃reached 51.55%.Thermally-induced crosslinking modification increased the tensile strength（TS）of the CS film,but decreased its elongation at break（EB）.Especially,the TS of the C110 film was the highest level of 54.3 MPa,which was nearly 4 times higher than that of C25.The ultraviolet,water vapor,and oxygen barrier capacity of all the CMR films was enhanced.By contrast,the water content（WC）,water solubility（WS）,and swelling degree of all the CMR films were reduced.Compared with that of the C25 film,the value of the C110 film decreased by 48.3%,62.7%,and 93.5%,respectively.In summary,the thermally-induced crosslinking modification strategy improved the mechanical properties,barrier ability,and water resistance of the CS film,and the comprehensive physicochemical indexes of the C110 film were better.Next,the effects of different concentrations of cinnamaldehyde nanoemulsions（CANE,2%,4%,6%,8%,and 10%）and tea polyphenol（TP,0.02%,0.04%,0.06%,and 0.08%）on the microstructural,physicochemical,antibacterial,antioxidant,and slow CA controlled-release of properties of the CMR/ADA-CA/CS-TP films were studied.For CMR/ADA-CA/CS trilayer composite film,FTIR analysis indicated that Schiff base,hydrogen bond,and electrostatic interaction existed between the trilayer film.Crystal structure of the composite film by XRD showed that the components have good compatibility.SEM images presented a clear and cohesive trilayer structure.The appearance of all the films was observed a uniform and transparent surface,indicating that their packaging performance was good and they did not affect the observation of the packaged food.The color and ultraviolet blocking capacity of the films were gradually enhanced with the increase of CANE concentration,but the influence of adding 6%-10%CANE on the color and transmittance of the film was little changed.The increase in CANE concentration increased the TS and EB of the films.The TS and EB values of the films supplemented with 6%-10%CANE were close to 1.6-1.7 times and 1.2-1.3 times of the film without CANE,respectively.Water vapor permeability（WVP）and oxygen permeability（OP）of the films decreased first and then increased with the increase of CANE concentration.The lowest value appeared at 8%CANE addition,and the WVP and OP of the corresponding film decreased to 44.7%and 57.6%of the control film,respectively.In the food simulants（10%and 95%ethanol）,the trilayer films had a slow-release effect on CA.The increase in CANE concentration improved the antioxidant properties of the films with a positive correlation trend.In addition,the antibacterial effect of films containing 2%-4%CANE was weak.More than 8%CANE concentration was added in the films,their inhibition effects on the Staphylococcus aureus and Escherichia coli.were no longer significantly reduced（p（29）0.05）.Overall consideration,the addition 0f 8%CANE was preferred.For CMR/ADA-8%CANE/CS-TP trilayer composite film,the hydrogen bond between TP and CS was demonstrated by FTIR.The increase in TP concentration deepened the color of the film and decreased its transmittance.Compared with the control group,the total color difference of the film with 0.08%TP increased by 2 times,and the whiteness index decreased to 25.3%.With the increase of TP,the TS of the film increased first and then decreased,and reached the maximum at the concentration of 0.04%TP.However,the EB of the films was almost constant,ranging from 19.59%to 22.21%.The addition of TP reduced the water vapor,oxygen barrier ability,and water resistance of the films.Moreover,the DPPH·free radical scavenging ability of the films with 0.06%-0.08%TP was more than 81%,and there was little difference in the inhibition effect on the Staphylococcus aureus and Escherichia coli.Overall consideration,the addition 0f 0.06%TP was preferred.At last,optimized C110/ADA-8%CANE/CS-0.06%TP film was prepared and the preservation effects of different processing methods（unwrapped（CK group）,commercial PE wrapped（PE group）,pure chitosan film wrapped（CS group）and trilayer composite film wrapped（AF group））on the quality of grass carp fillets were evaluated.Within 8 d of storage,AF group had no bad effect on fish color and pH.The texture,total volatile basic nitrogen（TVB-N）,thiobarbituric acid-reactive substances（TBARS）,hydrosulfuryl content（-SH）,and microbial inhibition of fish in CS and AF groups were better than those in CK and PE groups.This was because the trilayer composite film had good oxygen barrier,antioxidant and antibacterial properties,which can inhibit lipid oxidation,protein oxidation,and the rapid propagation of pseudomonas and H₂S-producing bacteria.On the 8 d of storage,the TVB-N,TBARS,oxidized-SH contents,and total viable counts in the AF group were decreased by45.7%,50.7%,68.0%,and 2.33 log₁₀CFU/g compared with CK group,respectively.In conclusion,chitosan/alginate dialdehyde trilayer films incorporated with cinnamaldehyde and tea polyphenol could prolong the shelf life of fish and have the potential to be used as active packaging for food preservation.