| With the rapid development of microencapsulation technology in food,pharmaceutical,chemical industry and other fields,the application of microencapsulation in food packaging has gradually become a research hotspot.One of the primary ways to combine microencapsulation technology with packaging technology is to use microencapsulation technology to encapsulate antimicrobial substances,and then mix microcapsule with polymer matrix to prepare the antimicrobial active packaging film.This kind of film can enhance the stability of active substances,give packaging antibacterial activity and slow-release,can slowly release bacteriostatic substances to food and prolong the shelf life of food.For the polymer substrates,potato starch has great application prospect in food packaging due to many advantages,such as wide source,low price,recyclability,high transparency and good film-forming properties.In this study,thyme essential oil based oil-in-water microemulsion was used as core material to prepare thyme oil microcapsules by layer-by-layer self-assembly.Potato starch was used as film substrate to prepare composite film by adding thyme oil microemulsion or microcapsule as antibacterial agents.The release,antimicrobial and preservation effects of antibacterial film on chilled meat were studied.The main research contents and results are as follows:1.Self emulsifying preparation of thyme essential oil microemulsion was designed to increase the loading capacity of thyme essential oil and reduce the amount of surfactant.The structure types of microemulsions were identified by conductivity method,rheological method and staining method.Oil percolation threshold was predicted by conductivity method,and oil-in-water region was accurately divided on pseudo-ternary phase diagram.The influence of different factors like surfactant,cosurfactant,temperature and aqueous phase on the formation of microemulsion as well as the storage stability of microemulsion was investigated.The maximum area of oil-in-water microemulsion,that is,the highest oil loading formula was obtained.The formula was: the surfactant was polyoxyethylene hydrogenated castor oil / Span 80=2:1(w/w),the temperature was 25 ?,the water phase was deionized water,the mass ratio of surfactant to thyme oil was 2:1,the O/W microemulsion area was 3.68%,and particle size of microemulsion was 11-14 nm.2.The microemulsion with 80% water content prepared with the formula of the largest O/W microemulsion area was used as the core material,and the encapsulation rate,yield and thyme oil content of microcapsules were taken as indicators to optimize the preparation process of thyme essential oil microcapsules in order to obtain microcapsules with stable and excellent properties.The mass concentration of quaternary ammonium salt of chitosan and carboxymethylcellulose sodium was 1.25 mg/mL and 1.0 mg/mL,respectively.The pH of wall material was 6.5,the NaCl concentration of wall material was 0.1 mol/L,the assembly temperature was 30 ?,and the volume fraction of 2.5%(m/v)glutaraldehyde solution as curing agent was 6% of the total volume of microcapsule solution and cured for 2 hours at 4 ?.By orthogonal test,in the best condition,the encapsulation efficiency of microcapsule was 91.35%,the yield was 84.79%,and the thyme oil content was 0.056 ?L/mL.3.Potato starch was used as the film forming substrate,and the active composite film was prepared by adding thyme oil microemulsion or microcapsule.The release performance of the films was studied.In the release medium of PBS/ ethanol =4:1(v/v),the cumulative release rate of starch film containing 5% thyme oil,microemulsion and microcapsule at 20 h was 96.53%,56.71% and 41.83%,respectively,indicating that the thyme oil microemulsion film and microcapsule film had sustained release effect.4.The antibacterial effect of composite membrane on Staphylococcus aureus and Escherichia coli were studied.PE film and potato starch film had little inhibitory effect.The bacteriostatic effect of microemulsion film and microcapsule film increased with the increase of microemulsion or microcapsule concentration,and the inhibition effect on Staphylococcus aureus was stronger than that on Escherichia coli.The microemulsion film had stronger bacteriostatic effect than the microcapsule film.5.The effects of composite film on pH,color,sensory quality and total bacterial count of chilled meat were studied.When stored at 0-4 ?,thyme essential oil microemulsion film and microcapsule film had good preservation effect on chilled meat.The overall preservation effect was blank < PE film < 2.5% microcapsule film < 2.5% microemulsion film < 5% microemulsion film < 5% microcapsule film,but the composite film had little effect on the redness value of chilled meat.Compared with microemulsion film,the slow release of thyme essential oil in microcapsule film was more durable and effective.The shelf life of potato starch-based film with 5%(v/v)microcapsule for chilled meat stored at 4 ? was about 14 days,while that of control group and PE film was 6 days and 10 days,respectively. |
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