Construction Of Gliadin/Carboxymethyl Chitosan Nanosystem Co-Encapsulated Natamycin-Theaflavins And Its Application In Edible Antibacterial Film

As a natural preservative,Natamycin（Nata）has a good inhibitory effect on filamentous fungi and yeast,but its low water solubility and light instability limit its application in food.In this paper,Nata was embedded in a nanocarrier system constructed by Gliadin/Carboxymethyl chitosan（CMCS）to improve its water solubility,and its photostability was improved by co-embedding Theaflavins（TFs）.Firstly,the stabilized Gliadin nanosystem by CMCS was constructed,and its stability and physicochemical properties were investigated.Secondly,the physicochemical and antibacterial properties of Glia-CMCS nanosystem for co-embedding Nata and TFs（TNGC nanosystem for short）were investigated.Finally,nanosystems were used as antibacterial,antioxidant and structural strengthening additives in CMCS edible films.The results of this paper provide a feasible scheme for the application of natamycin in food and the development of functional edible films.The main research contents and conclusions of this paper are as follows:Firstly,the CMCS-stabilized Gliadin nanosystem was prepared by antisolvent method.The solubility of Gliadin in 70%ethanol was determined to be 3.9±0.1 mg/m L by solubility method.The optimized preparation conditions were as follows:the mass ratio of Gliadin to CMCS was 1:0.5.Under the optimum conditions,the particle size,zeta potential and PDI of Gliadin-CMCS nanosystem are 315.1±19.5 nm,5.6±0.7m V and 0.22±0.01,respectively.The protein content in the supernatant was 97.44±1.79%.The turbiscan stability index（TSI）of Gliadin and Glia-CMCS nanosystems after 1d was 15.7 and 1.0,respectively.The stability of Glia-CMCS nanosystem at different pH and salt ion concentration was investigated.When the pH is 5,the particle size,zeta potential and PDI of Glia-CMCS nanosystem were 508.1±36.6 nm,-1.3±0.6m V and 0.59±0.05,respectively.When the salt ion（Na Cl）addition is 100 ppm,the particle size of Glia-CMCS nanosystem is 304.77±2.15 nm.The results show that Glia-CMCS is obviously superior to Gliadin nanosystem.The results of FTIR spectrometer showed that no new covalent bond was formed between Gliadin and CMCS.Secondly,the photostability of Nata is realized,the water solubility of Nata is improved,and the nanosystem has antioxidant and antibacterial abilities by co-embedding TFs.The degradation rate decreased from 90.07±0.02%to 38.44±0.03%in 50 ppm Nata solution with 25-200 ppm TFs when irradiated by ultraviolet light with power of 20 W and wavelength of 254 nm for 1 hour.TNGC nanosystem containing 200 ppm TFs and 0-100 ppm Nata was prepared.The average particle size and zeta potential of the nanosystem was 120 nm and-30 m V.The embedding rate and loading rate of Nata ranged from 30.92±0.04%to 34.54±0.04%and 0.65±0.10%to 2.48±0.27%,respectively.Through the methods of DPPH and FRAP,it is proved that the nanosystem has antioxidant capacity.The inhibition zone method proved that the nanosystem had the characteristics of inhibiting Aspergillus Niger.When the nanosystem was irradiated by ultraviolet light,the diameter of inhibition zone increased with the increase of TFs content,which proved that TFs had the function of protecting Nata from photodegradation.The results of molecular docking show that the interaction between Gliadin and TFs is van der Waals force,hydrogen bond and hydrophobic interaction.The interaction between Gliadin and Nata is van der waals force and hydrogen bond.Finally,the effect of adding TNGC nanosystem on CMCS edible films and its application in cheese were investigated.The dosage of CMCS for preparing films was optimized,and the condition of film-forming solution was 2%（w/v）CMCS.With the increase of nanosystem content in the film,the a*value of color of the film is from-0.28±0.05 to 0.68±0.09,and the b*value is from 0.98±0.09 to 2.36±0.22.The opacity has also increased,from 0.50±0.15 to 11.87±1.82,which can better block ultraviolet light.Through the tests of mechanical properties and water vapor permeability,it was found that the elongation at break and tensile strength of the films with 50%and 70%nanosystem were increased.The lowest water vapor permeability of 50%TNGC film is 1.92±0.26*10^-8*g*PA^-1*m^-1*s^-1.Through the measurement of water contact angle,it is found that the outer layer of the film is hydrophobic and the inner layer is hydrophilic.The film can not only block the invasion of external moisture,but also fit the food surface well.The antibacterial test proved that the film had a certain inhibitory effect on Aspergillus Niger.50%and 70%TNGC films can effectively inhibit the growth of mold on cheese surface.