| Star anise essential oil is a natural plant essential oil extracted from dried star anise fruit.It has good anti-oxidation activity and antibacterial activity.However,due to its low solubility in water,strong volatile and unstable physicochemical properties,its application is limited.In this study,the extraction method of anise essential oil was optimized.The inclusion complex of star anise essential oil was prepared by cyclodextrin molecular inclusion technology,and its inclusion mechanism was investigated.In addition,using sodium alginate as the film-forming substrate,a composite film system was constructed by adding star anise oil and inclusion complex.Furthermore,the composite membrane was applied to preserve the color and freshness of fresh-cut yam.The main research contents and results are as follows:(1)Study on extraction process of star anise essential oil.Taking the gan-zhi star anise as the research object,the yield,aroma performance,composition and biological activity of anise essential oil obtained by steam distillation,ethanol Soxhlet extraction,supercritical carbon dioxide extraction and sub-critical n-butane extraction were different.By comprehensive evaluation for yield and biological activity,ethanol Soxhlet extraction was determined as the best extraction method.The correlation analysis confirmed that the relative contents of volatile trans-Anethole,Estragole,D-Limonene,Eucalyptol and trans-?-Bergamotene in essential oil had a strong correlation with the antibacterial activity of essential oil.And the contents of volatile D-Limonene,Eucalyptol and non-volatile total flavonoids and polyphenols had a strong correlation with the DPPH scavenging activity of essential oil.On the basis of single factor experiment,the optimal extraction conditions were determined by Box-Behnken central composite design of response surface method.The optimum extraction conditions of ultrasonic-assisted ethanol Soxhlet extraction were as follows:ultrasonic frequency 80 KHz,crushing particle size 60 meshes,liquid-to-material ratio 8:1(mL:g),ultrasonic treatment for 35 min.Under these conditions,the yield of essential oil was 25.51%+0.21%.(2)Inclusion of anise essential oil with different cyclodextrins.It was confirmed by phase solubility test that?-,?-and hydroxypropyl-?-cyclodextrin can form an inclusion complex with star anise essential oil with a molar ratio of 1:1 in addition to?-cyclodextrin.Based on the inclusion const ant and solubilization factor,hydroxypropyl-?-cyclodextrin was identified as the best cyclodextrin for inclusion of star anise essential oil.The inclusion consta nt is 3688.869 L/mol at 55°C and the water solubility of essential oil can b e increased to 21.695 times at the same temperature.The results of thermodyn amic parameters analysis showed that the inclusion of four cyclodextrins on sta r anise oil was an endothermic reaction with entropy increase,and the increase of disorder was the main driving force of inclusion reaction.(3)Preparation,properties,characterization and inclusion mechanism of star anise essential oil/hydroxypropyl-?cyclodextrin inclusion complex.The inclusion rate was selected as the evaluation index.Based on the single factor experiment,the optimal inclusion condition was determined by quadratic regression orthogonal rotation combination design:the concentration of hydroxypropyl-?-cyclodextrin was 2.8%,and the inclusion time was 67.6 hour,the inclusion temperature was 27.0°C,and the maximum inclusion ratio was 51.5%±0.49%.The formation of inclusion complex and the encapsulation structure of the host-guest were confirmed by TEM,SEM,UV,FT-IR and ~1H NMR analysis.The trans-Anethole and the quercetin,which was representative of the flavonol and polyphenols,were selected as the prototypes,the inclusion mechanism was inferred by spectral data and molecular simulation as follows:the benzene ring in essential oil molecule entered the cavity of cyclodextrin through hydrogen bond and van der Waals force,and the inclusion complex molecular structure was the side of benzene ring connected with ether bond in trans-Anise molecule and the A ring in the quercetin molecule was close to the large mouth of cyclodextrin molecule.Due to the encapsulation selectivity of cyclodextrin,the components of star anise essential oil have some loss during the inclusion process,which lead to the decrease of its biological activity,but its volatilization stability,light stability and thermal stability were improved significantly(p<0.05).(4)Preparation and characterization of sodium alginate active composite film containing star anise essential oil/cyclodextrin inclusion complex.Sodium alginate was used as the film-forming substrate,and glycerin was used as the plasticizer,the optimum film forming concentration was determined to be 2%by comprehensive evaluation of tensile strength,elongation at break and water vapor permeability.The sodium alginate composite film systems were constructed by adding anise essential oil or inclusion compound to the blank film solution.The TEM,SEM,UV,FT-IR and ~1H NMR analysis confirmed the electrostatic and hydrogen bond interactions between the anise essential oil(or the inclusion complex)and sodium alginate.The composite film system models were simulated by Hyperchem 8.0 MM+optimization method,and the composite films with different proportions were compared.The results showed that the ratio of the number of molecular chains of sodium alginate to the number of molecules of free compound in the essential oil(or inclusion complex)was 3:1,and the energy of the whole system was the lowest.Moreover,its properties were analyzed.In the concentration range of 0.5 mg/mL to1.0 mg/mL,the addition of essential oil or inclusion complex reduced the mechanical properties of composite films in varying degrees,but significantly improved the antibacterial activity and DPPH free radical scavenging activity of sodium alginate(p<0.05).The inclusion complex composite film with the same essential oil dosage has better inhibitory effect on Rhizopus stolonoifer than the essential oil composite film,while the essential oil composite film has better DPPH scavenging activity.The light stability of the inclusion complex composite film was better than that of the essential oil composite film(p<0.05)under the irradiation of 8 W ultraviolet light and dark conditions,and its the slow-release and thermal stability were better than those of the essential oil composite film.(5)The application of compound film in preserve the color and freshness of fresh-cut yam.The constructed compound films of anise essential oil and inclusion complex were applied to preserve the color and freshness of fresh-cut yam.The results showed that during the 8-day simulated storage test,blank treatment films had a little effect on the browning inhibition and prevent VC loss of fresh-cut yam,and the protective effect was further enhanced by adding essential oil and inclusion compound films.It is related not only to the natural oxygen barrier formed by sodium alginate,but also to the activity of the anise star essential oil.In addition,the inclusion of the hydroxypropyl-?-cyclodextrin improved the water solubility of the essential oil and made it have some sustained release property,which further enhanced the color protection and freshness preservation function of the composite films.However,compared with the blank films,the inhibitory effect of the composite film system on water loss of fresh-cut yam was not significant(p<0.05).In this study,a novel active composite film material was constructed by blending anise star essential oil/cyclodextrin inclusion complex to a traditional sodium alginate matrix material.The properties and structural characteristics of the product were researched and applied to preserve the color and freshness of fresh-cut yam.It layed a foundation for studying the micro-nano materials of plant essential oil and their application in active packaging film,and provided a basis and reference for expanding the application of plant essential oil in the field of food preservation. |
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