Preparation And Properties Of Phenolic Acid-chitosan Composite Films For Food Packaging

The application of chitosan?CS?film in the field of food packaging has been limited due to their relatively low mechanical properties,antioxidant and antibacterial activities.Therefore,many related researches are devoted to finding materials from a wide range of sources that can ensure food safety,high antioxidant and antibacterial activities to improve properties of the CS film.Recently,in order to expand the application of CS film in the field of food packaging,there has been a growing interest in the modification of CS film with natural polyphenols.Polyphenols?such as tea polyphenols,gallic acid,curcumin,etc.?are often added to CS film by conjugated or incorporated to prepare the corresponding polyphenol-chitosan conjugated films or incorporated films.Compared to CS film,polyphenol-chitosan conjugated films or incorporated films have significantly improved various properties of the composite films,especially in antioxidant and antibacterial properties.However,there is less report about the comparison of conjugated films with incorporated films on the properties of composite films.The chlorogenic acid-grafted-chitosan conjugates?CA-g-CS?with three different grafting ratios were synthesized by carbodiimide mediated coupling reaction,the grafting ratios of CA-g-CS was 60.11,170.31 and 250.13 mg/g according to the Folin-Ciocalteau method.Then the CA-g-CS conjugated films?CA-g-CS?,CA-g-CS?,and CA-g-CS??and the CA-CS incorporated films?CA-CS?,CA-CS?,and CA-CS??with equivalent CA content were prepared,respectively.The physical,mechanical,antioxidant and antibacterial properties of CA-g-CS conjugated and CA-CS incorporated films were evaluated.The results showed that the thickness of the conjugated films were not significantly different from that of the CS film,but the thickness of the incorporated films increased.The opacity of the conjugated films decreased,the opacity of the incorporated films increased,water content of conjugated and incorporated films decreased,but water solubility,water vapor permeability?WVP?,antioxidant and antibacterial properties of conjugated and incorporated films increased with the increasing of CA content.Compared with incorporated films,conjugated films possessed higher water solubility and lower WVP with equivalent CA content.CA-g-CS?had the lowest WVP(0.92±0.02×10^-7 g mm/h cm² Pa).The mechanical properties of the incorporated films were better than those of the conjugated films,but the antioxidant and antibacterial activity of the conjugated films were better than that of incorporated films.CA-g-CS?showed 87.4%DPPH radical scavenging activity,and its inhibition zone diameter against Staphylococcus aureus reached 17.61 mm.Salicylic acid was grafted onto chitosan to synthesize salicylic acid-grafted-chitosan conjugates?SA-g-CS?under the same reaction conditions for the synthesis of CA-g-CS.The grafting ratios of SA-g-CS were determined by the Folin-Ciocalteau method as 40.70,85.45 and 105.71 mg/g.The SA-g-CS conjugated films?SA-g-CS?,SA-g-CS?,and SA-g-CS??and the SA-CS incorporated films?SA-CS?,SA-CS?,and SA-CS??with equivalent SA content were prepared,respectively.The physical,mechanical,antioxidant and antibacterial properties of SA-g-CS conjugated films and SA-CS incorporated films were evaluated.The thickness of the conjugated films were not significantly different from that of the CS film,the thickness of the incorporated films increased,the opacity,water content and WVP of conjugated and incorporated films did not change significantly,but the water solubility,antioxidant and antibacterial activity were enhanced with the increasing of SA content.Compared with incorporated films,conjugated films possessed higher water content,water solubility,antioxidant,antibacterial activity and lower WVP with equivalent SA content.The mechanical properties of the conjugated and incorporated films were related to the content of SA.The tensile strength of SA-g-CS?and SA-g-CS?were lower than that of CS film,but its elongation at break were enhanced.The tensile strength of SA-g-CS?which higher grafting ratios were increased to 67.36MPa,but reduced elongation at break.The incorporated films possessed better tensile strength than CS film,SA-CS?and SA-CS?possessed better tensile strength than SA-g-CS?and SA-g-CS?.CS film,CA-g-CS?,CA-CS?,SA-g-CS?,and SA-CS?were chosen to evaluate the preservative effect on Penaeus vannamei at 4±1?.The changes of weight loss,p H,total volatile basic nitrogen?TVB-N?,total bacterial count and sensory score of shrimp during the 8 days storage were determined.The results showed,conjugation and incorporation of CA or SA effectively delay the increase of these indicators.The p H of shrimps threated with CA-g-CS?was 7.1,TVB-N was 18.17 mg N/100 g,total bacterial count was 4.9 log CFU/g,sensory score was 5.3 on the 8th day of the storage.And the p H threated with CA-CS?packaging group was 7.3,TVB-N was 20.87 mg N/100 g,total bacterial count was 5.1 log CFU/g,sensory score was 4.7.The p H value of Penaeus vannamei treated with SA-g-CS?on the 8th day was 7.5,TVB-N was 23.48 mg N/100g,total bacterial count was 5.5 log CFU/g,and the sensory score was 4.5.The p H value threated with SA-CS?packaging group was 7.7,TVB-N was 26.1 mg N/100 g,total bacterial count was 5.9 log CFU/g,and the sensory score was 3.The above showed that both CA and SA can be used as modified materials.Compared to CS film,the films with conjugated and incorporated CA or SA exhibited positive effect on the preservation of Penaeus vannamei,wherein the conjugated films had the best preservative effect.