| Due to heightened awareness of food safety and the need for environmental protection,the development of a safe and environmentally friendly natural edible film has become a hot topic in the field of food research.Flaxseed gum(FG)has good edible properties,antioxidant properties,and film formation characteristics,but its poor mechanical properties limit its applications.In this study,FG was extracted by ultrasound-assisted extraction,with FG and chitosan(CS)as the film forming substrate,cassia bark aldehyde(Cinnamaldehyde,CIN)as the antibacterial agent,blueberry anthocyanins(BA)as the indicator agent,made a sandwich structure with FG/CS,FG/CS/CIN antibacterial film and FG/CS/BA intelligent film with a p H color response.The physicochemical properties,structure,and functional properties of the composite film were studied systematically.The two types of films were applied to the preservation of pork and fish,providing theoretical support for the research,development,and application of functional multilayer films.The main results are as follows:(1)FG was prepared by ultrasound-assisted extraction,and its structure was characterized to investigate its functional properties.The results show that the FG prepared by ultrasound-assisted extraction has low molecular weight(767 KDa)and a concentrated molecular weight distribution.Its monosaccharide composition is mainly arabinose,xylose,and galacturonic acid,negatively charged in the range of p H 3 to 11,and it is a noncrystalline substance.The flaxseed gum structure has a characteristic polysaccharide absorption peak,loose structure,and good thermal stability;it is a non-Newtonian fluid and has good oxidation resistance.(2)FG film liquid and CS film liquid were prepared as a "sandwich" multilayer film using a multilayer fluid delay method to determine the influence of different factors on the properties and structure of the multilayer film.Through principal component analysis,the optimal preparation conditions for multilayer films were determined to be: FG film liquid and CS film liquid at 20:10(v/v),chitosan concentration at 1.0%(w/v),and glycerol addition at 21%(w/w).The comprehensive performance of multilayer films prepared under these conditions was 0.724.Compared to the pure FG films,the mechanical properties,barrier properties,and thermal stability of these multilayers were significantly improved,and the light transmittance was reduced.During the film formation process,a dense mesh structure was formed due to new forces between the FG and CS molecules,which then improved the performance of the multilayer film.(3)CIN was added to the middle layer of the FG/CS film,and the effects of different CIN additions on the properties and structure,as well as the effect of the antibacterial film on the quality change of cold pork,were investigated.The results show that the optimal amount of CIN to add is 1.5%(v/v),which tensile strength,fracture elongation,oxygen transmittance,water vapor transmittance,and light transmittance were reduced by 27.34%,10.67%,13.51%,9.72%,and 12.63% compared with the FG/CS multilayer film.In the process of film formation,hydrogen bonds,electrostatic interactions,and C-O-C bonds were generated between the components and Schiff bases,which improved the crystallinity of the film.The film structure changed from a mesh to a sheet,which significantly improved the oxidation resistance of the film but had no significant effect on the thermal stability of the film.The antibacterial film showed higher antimicrobial activity against Staphylococcus aureus than against Escherichia coli.By destroying the integrity of the cell wall and cell film of the bacterial body,it eventually led to the death of the organism.The shelf life of pork treated with antibiofilm can resch 8 d,which was effectively extended by 4 d compared with the control group.(4)Based on the prepared FG/CS,BA was added to the outer film to construct a smart film with a p H color response.The color change of BA in different p H solutions was analyzed,and the structure of the smart film and its responsiveness to different p H solutions and volatile ammonia was characterized and applied to the monitoring of fish body freshness.The results show that BA reduces the mechanical properties,oxygen barrier properties,and light transmittance of the intelligent film but improves the water vapor barrier capacity,changes the internal structure of the film,and reduces the thermal stability.The intelligent composite film showed good color response to both changes in p H and the presence of volatile ammonia.In the monitoring of fish freshness,it was found that with prolonged storage time,the p H and TVB-N values of the fish increased.The color of intelligent composite film changes from light purple to light gray,and finally to yellow also changed,which could play the role of an indicator. |
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