Preparation And Antioxidant,Antibacterial Activity Of The Citrus Peel/Bacterial Cellulose Composite Films

The non-biodegradability of petroleum-based plastics has a severe negative impact on the environment,and there is a growing trend in the use of biodegradable polymers as food packaging and medical wound dressings.New food packaging materials not only have to be improved in mechanical and physical properties,but also require improved properties such as their antioxidant activity.The citrus fruit processing industry produces a large amount of peel residue,which will cause serious ecological problems if it is discarded or improperly handled.Citrus peel is rich in polyphenols and other bioactive substances,which have good antibacterial and antioxidant effects.In this experiment,citrus peel powder was used as the matrix,and BC with high degree of polymerization,high crystallinity and high purity was added to the citrus peel matrix as a reinforcing agent.Using the unique three-dimensional network structure of BC to improve the mechanical properties of the composite film,a biologically active packaging material was prepared.This will allow for good recycle and re-use of citrus peel residues.Finally,sorbic acid was added into the composite material to endow the composite packaging material with antibacterial property.The main content and results of this experiment are as follows:(1)3%and 5%(w/w)citrus peel suspensions were prepared respectively,and plasticizer glycerol was added to obtain citrus peel composite films.Then the active films were prepared by adding four concentrations of BC(0%,5%,10%,and 15%)into the citrus peel suspensions.(2)The CP/BC composite films were characterized by scanning electron microscopy,X-diffraction rays and infrared spectroscopy.The results showed that:The surface structure of the composite films were observed by scanning electron microscope,and them were found that with the addition of BC,the holes on the surface of the composite films have been decreased,became smoother,and formed a denser surface layer;Through X-diffraction rays analysis,there was found that the addition of BC made the X-diffraction peaks higher and sharper,indicating that the addition of BC increased the polymerization degree of the films,and the internal network structure of the films were more uniform and dense.Using Fourier transform infrared spectroscopy analysis,there was found that no new peaks appeared after the interaction between the citrus peel matrix and BC molecules,indicating that the two showed good biocompatibility.With the increase of BC content(0%-15%),the water content of 3%and 5%(w/w)CP/BC composite films decreased to 10.58%and 20.20%,the swelling degree decreased to 10.15%and 13.10%,the solubility drops to 23.09%and 28.02%,the porosity drops to 21.26%and 30.63%These results indicated that the addition of BC makes the composite films form a denser network structure,which hinders the interaction between the composite films and water molecules.These also indicate that BC is beneficial to maintain the stability of the membrane structure.By measuring the mechanical properties of the composite films,when the BC content of the 3%citrus peel composite films were 10%,the maximum load of the composite films were increased from 11.31 N to 19.84 N,and the tensile strength was increased from 4.92 MPa to 8.34 MPa.The results showed that hydrogen bonds were formed between BC and the citrus peel matrix,and with the increase of BC concentration,the crosslinking density of the two increased,showing a significant increase in the tensile strength of the composite films.However,when the BC content was increased to 15%,the mechanical strength was reduced to 7.87 MPa.A high concentration(15%)of BC will reduce the interaction force between the polymers,thus resulting in a relative decrease in mechanical properties.(3)After measuring the properties of the composite films,the optimal process conditions for the BC composite films based on the citrus peel matrix were determined as:3%citrus peel powder,10%BC.(4)By measuring the total phenolic release of the active composite films,the total phenolic release of the 3%citrus peel/bacterial cellulose composite film was 0.0091 mg/g when reacted in the alcohol food simulant for 60 mins,while the total phenolic release in the fat simulating system was 0.0061 mg/g.indicating that the active composite material could exert stronger antioxidant effect in foods with lower fat content.The scavenging activities of the modified composite films on ABTS and DPPH radicals were tested,and the results showed that the scavenging activity of 3%CP/BC composite films were 99.29%for ABTS free radicals,and the scavenging activity for DPPH free radicals were 95.60%,indicating that the CP/BC composite films had good antioxidant activity.(5)The CP/BC composite films with different concentrations of sorbic acid were added to test the antibacterial ability of bacteria and S.cerevisiae.The results showed:The inhibition rates of 20%sorbic acid against E.coli,P.aeruginosa,S.aureus,B.subtilis and S.cerevisiae were 85.53%,78.53%,77.66%,69.90%and 94.21%.These indicated that the sorbic acid-modified composite films had stronger inhibitory ability to G~--bacteria than G~+-bacteria,and better inhibitory ability to S.cerevisiae.Although the antibacterial properties of SA/CP/BC active composite films are still lower than many antibiotics,they still have certain application value in food packaging and medical dressings.