| Packaging materials prepared from starch need to meet requirements such as water vapour barrier,biodegradability and mechanical properties.Especially when applied to food packaging,the safety of the food needs to be ensured.At present,research on starch-based packaging has been carried out on single-layer films,the functionality of which cannot fully meet the requirements of food packaging.Therefore,this paper will explore the preparation of a starch-based antibacterial packaging with hydrophobic function and its performance study.In order to meet the different functional requirements of food packaging,starch-based multilayer composite film materials were prepared in this study.Polyvinyl alcohol can be used as an intermediate layer due to its good insulation from water vapour and oxygen,as well as its good ductility and adhesion.The outer layer in contact with air was modified with hydrophobic properties to produce a modified starch layer with hydrophobic properties.The inner layer in contact with food is treated with antimicrobial treatment to prepare an antimicrobial starch film,which is made with microencapsulation technology to give the antimicrobial film a slow-release antimicrobial effect.After drying,three layers of hydrophobic modifier are sprayed on in stages and left to dry to produce a hydrophobic antimicrobial starch multilayer composite film.In this study,PVA/modified starch bilayers were firstly prepared.The original starch was modified with stearic acid,and the addition of 3%stearic acid modified starch had the highest degree of substitution.X-ray diffraction and Fourier infrared spectroscopy analysis showed that the-OH of starch bonded with-COOH of fatty acids and the hydrogen bonding increased,which proved the formation of starch esters.Next,the effect of cellulose nanofilaments(CNF)on the tensile strength of the starch film was investigated,and when the amount of 0.4%,the The highest tensile strength was found at a dosage of 0.4%and a temperature of 95℃ at the time of addition.Different lamination ratios of PVA/modified starch(100/0,85/15,75/25,65/35,50/50,0/100)were investigated,and the best tight lamination ratio of 50/50 was obtained by scanning electron microscope analysis.three layers of homemade hydrophobic modifier were sprayed onto the bilayer film,and the lowest water vapor transmission rate of 0.3×10-10 g.cm/cm2.s.Pa.Therefore,the PVA/modified starch ratio of 50/50 was chosen for the subsequent study.The antibacterial film preparation process method was investigated,and firstly,the antioxidant properties of cinnamaldehyde(CIN),thymol(THY)and CIN-THY complex were studied by the method of free radical scavenging,and it was found that the antioxidant properties of CIN-THY complex were better,and the antioxidant properties of different CIN-THY ratios(5:1,3:1,2:1,1:1)The antioxidant properties of different CIN-THY ratios(5:1,3:1,2:1 and 1:1)were analyzed and it was concluded that the best antioxidant properties were obtained at 1:1.By using the complex coalescence reaction as the preparation method,the microcapsules were prepared by using CIN-THY complex as the core material and gelatin(GE)and gum Arabic(GA)as the wall material.Next,the amount of microcapsules added and the drying temperature of the antimicrobial film were investigated,and the mechanical properties of the antimicrobial film were analyzed,and the tensile strength of the starch antimicrobial film reached 20.3 MPa at 1.5%of microcapsules added and a drying temperature of 50℃,which had the optimal mechanical properties.It can be seen by scanning electron that the surface of microcapsules is smooth,without folds and hollows.The antimicrobial film can be clearly seen that the microcapsules are uniformly distributed on the surface and inside of the film,and the combination of Fourier infrared spectroscopy and thermogravimetric analysis indicates that the microcapsules are successfully encapsulated.The results of the slow release tests of microcapsules and antimicrobial membranes in four(distilled water,3%acetic acid,10%ethanol,95%ethanol)food simulation systems showed that the release rate of CIN-THY microcapsules in distilled water and 3%acetic acid systems was slower and the slow release performance was more stable,which was more suitable for use in neutral and acidic.Compared with microcapsules,the antioxidant properties,bacteriostatic properties and slow release properties were significantly improved after making microencapsulated starch composite films.Finally,antimicrobial starch/PVA/modified starch composite films were prepared and their applications were investigated.The antimicrobial film and PVA/modified starch bilayer films were laminated in different ratios(80/20/0,68/17/15,60/15/25,52/13/35,40/10/50,0/25/75),and the optimal layer and ratio of 40/10/50 was obtained,and the water vapor barrier was greatly improved.The contact angle maximum value of 120.1°,WVP minimum value of 1.3×10-10 g.cm/cm2.s.Pa,and tensile strength were also improved to a maximum value of 27.1 MPa.thermogravimetric analysis yielded a more stable thermal stability for the 40/10/50 composite film compared to the single-layer antimicrobial film.The slow release performance was measured in four food simulated environments,showing that the multilayer composite film is more suitable for use in neutral and acidic environments.Finally,the mold rate of bread was measured,and the results showed that the multilayer composite film could effectively delay the mold deterioration of bread and and extend its shelf life to 6 days.compared with the blank group because the multilayer composite film continuously released antibacterial substances and could stop the growth of microorganisms for a longer period of time. |
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