| Eucalyptus essential oil(EEO)is a natural resource which is economically friendly and has broad-spectrum antibacterial activity,therefore has a promising application prospect in the preservation of fruits and vegetables.However,EEO in liquid form is unstable,volatile,insoluble in water,and corrosive at high concentration,making it difficult for storage and applications.In this thesis,EEO was embedded using ?-cyclodextrin(?-CD)to form microcapsules,the preparation conditions were optimized,and the effects of ?-CD capsulation on the antibacterial performance and compositions of EEO were studied.The structure and properties of EEO microcapsules were investigated,and the applications of EEO microcapsules as an antibacterial preservative or to make antibacterial fresh-keeping film in preserving litchi and cherry tomato were investigated.The results will provide information for the application of EEO and for developing natural antibacterial preservatives and antibacterial fresh-keeping films for fruits and vegetables.The main research contents and results are as follows:(1)Comparisons of the determination methods of oil content encapsulated in essential oil microcapsules.Commonly used methods including dry weight loss,determination of volatile oil and ultraviolet spectrophotometry were compared,and the results showed that they all had good precision and accuracy,with relative standard deviation(RSD)lower than 5% and the recovery between 90%~120%.Dry weight loss method had larger experimental errors and higher results,and are suitable for testing samples with large quantities.Ultraviolet spectrophotometry method had many influencing factors,but it had high detection speed,although it was not easy to operate and with high costs.The method by determining volatile oil was easy to operate and had low cost,but it was time-consuming.It could be used when 0.1 mL of essential oil could be distilled from the microcapsules.(2)The effects of ?-CD capsulation on the antibacterial performance and compositions of EEO.EEO had antibacterial activities on the tested bacteria both before and after encapsulation.Its antibacterial activities after encapsulation were slightly reduced,while its minimum inhibitory concentrations(MIC)were not influenced,and its minimum bactericidal concentrations for saccharomyces cerevisiae and penicillium citrinum were slightly increased.The gas chromatography-mass spectrometry results showed that before and after encapsulation,EEO had approximately the same main chemical compositions,including mainly terpenes and alcohols.And the relative amount of the main antibacterial ingredients such as pinene,cymene,limonene,terpilene,camphene and cineole were not apparently changed after encapsulation.These results show that microencapsulation did not greatly affect the antibacterial property and its main compositions of EEO.(3)The optimization of the preparation process through combining orthogonal and response surface methodology experiments.The results of orthogonal and Plackett-Burman experiments showed that the wall-core ratio,encapsulating temperature and encapsulating time were the main factors affecting the microencapsulating efficiency of EEO microcapsules,while the ethyl alcohol-EEO ratio and water-?-CD ratio were the secondary ones.Through the combination of orthogonal experiments and response surface methodology experiments,the optimal preparation conditions were determined as follows: encapsulating temperature 46?,encapsulating time 108 min,wall-core ratio 9.59,ethyl alcohol-EEO ratio 20:1,water-?-CD ratio 10:1.Under these conditions,the encapsulation efficiency and encapsulation yield were 71.17% and 86.30%,respectively.(4)The characterization of the structure and releasing properties of EEO microcapsules.The SEM micrographs showed that EEO microcapsules were parallel quadrilateral,and were orderly and densely packed with smooth surface.The particle size of EEO microcapsules showed normal distributions ranging between 5~45 ?m,and the average particle size was 18.6 ?m.The peak type and peak position of fourier transform infrared spectroscopy(FTIR)map showed that EEO microcapsules were successfully formed.Termogravimetry(TG)and differential scanning calorimetry(DSC)results showed that the thermal weight loss of EEO microcapsules was slow when the temperature was lower than 120?.Microencapsulation could significantly improve the thermal stability and delay the volatilization of EEO.The temperature and humidity improved the release of EEO microcapsules,and the release process of EEO microcapsules was between diffusion limit and first-order kinetics,which was in good agreement with Avrami's formula.(5)The applications of EEO microcapsules as an antibacterial preservative used in preservation at 6 ? of litchi and room temperature of cherry tomatoes.The results showed that EEO microcapsules could postpone the decline of sensory quality.It could also reduce the the oxidation of vitamin C and the consumption of titratable acid,total soluble solids etc.,sustain the nutritional quality of fruits.Compared with the control samples,it could increase the fresh-keeping period of fruits by 5 days for litchi and 2 days for cherry tomatoes.(6)The preparation of EEO microcapsules as antibacterial fresh-keeping film,and its application in the preservation of litchi and cherry tomatoes were studied.The results showed that EEO microcapsules could be used as an antibacterial preservative in the preparation of antibacterial fresh-keeping film.The konjac glucomannan(KGM)antibacterial fresh-keeping film has the best performance when using EEO microcapsules with the amount account for 0.6% of the amount of ionized water in the film.KGM antibacterial fresh-keeping film used in preservation at 6 ? of litchi and room temperature of cherry tomatoes could effectively reduce the evaporation of water,inhibit respiration,reduce the oxidation of vitamin C and the consumption of TA and TSS etc.And it could reduce the weight loss rate,and maintain the sensory quality of fruits,and therefore could extend the fresh-keeping period of both fruits by 2 days compared to control samples. |
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