The Preparation Of Compound Plant Essential Oil Microcapsule And Its Application In Peanut Storage Process

Peanuts are important oil plants and economic crops in China,which are easily susceptible to being infected by molds during the process of harvesting,transport and storage,causing the quick reproduction of molds and the production of mycotoxin in large quantities to seriously affect the safety of peanuts.Chemical anti-mildew agents are currently adopted to reduce the loss caused by mildewed peanuts,however,the accumulation of toxicity,environmental pollution and drug resistance by chemical anti-mildew agents are more outstanding.Therefore,it’s necessary to develop safe,effective and green anti-mildew agents for peanut storage.This research screened compound plant essential oils with good inhibiting effect on dominant molds during peanut storage from the five selected essential plant oils such as cinnamon,litsea cubeba,clove,thyme,citronella essential oils;in order to change their physical state and improve their stability,compound plant essential oils were microencapsulated and the manufacturing process was optimized;the compound plant essential oil microcapsules were used for peanut storage and their effects on microorganisms and quality of peanut during storage process were investigated.This thesis mainly consists of the following three parts:（1）Firstly,the compound plant essential oils with good inhibitory effect on the dominant molds during peanut storage were screened.Two moldy strains YQM and BQM isolated and purified from moldy peanuts were identified as Aspergillus flavus and Aspergillus niger by morphological and molecular biological methods,respectively.The single or compound inhibiting effects of five kinds of plant essential oils on YQM and BQM were evaluated via the bacteriostatic circle experiment,respectively,and the results showed that the inhibiting effects of compound essential oil consisting of cinnamon and litsea cubeba essential oils were most effective,and its diameters of the inhibition zones against YQM and BQM were 40.33mm and 39.80 mm at the concentration of 60μL/m L,respectively.The fractional inhibitory concentration（FIC）index calculated by minimum inhabitory concentration（MIC）implied that the inhibiting effects of cinnamon and litsea cubeba essential oils on YQM and BQM could be added,and the best volume ratio of cinnamon and litsea cubeba essential oils was3:5;results of scanning electron microscopy（SEM）displayed that cinnamon-litsea cubeba compound essential oil（CLCEO）was able to destroy the structure of the hyphae to inhibit the growth of molds.（2）Secondly,the optimal preparation conditions,characteristics and antibacterial properties of microcapsules of cinnamon-litsea cubeba compound essential oil（MCLCEO）were studied.Beta cyclodextrin was used as wall materials and molecular embedding method was adopted to produce MCLCEO,and the best producing conditions were as following:9.70%（w/w）wall materials being added,32.4℃for embedding temperature,10:1 for the ratio of outer materials and inside materials,determined by single factor and response surface experiments.The embedding rate of MCLCEO produced under the best conditions was 67.12%（w/w）.According to results of SEM,MCLCEO was a kind of regular cube crystal particles with even size.Based on infrared spectra,results showed that the CLCEO maybe enter the cavity structure of beta cyclodextrin assisted with the interaction between hydrogen bonds.The chemical composition of MCLCEO was analyzed by gas chromatography-mass spectrometry（GC-MS）and the results showed that MCLCEO could effectively preserve the key anti-fungal substances such as trans cinnamaldehyde and citral.In addition,MCLCEO had good antifungal activity against YQM and BQM,and the antifungal activity remained basically unchanged after two months’storage under 4℃.（3）Finally,the effects of MCLCEO on the surface microorganisms and quality of peanut kernels during storage process were studied.Peanuts of control groups（without MCLCEO added）and experimental groups[0.04%、0.12%and 0.20%（w/w）MCLCEO added]were stored for 35 d at 30℃.The results showed that MCLCEO not only effectively slowed down the increasing rate of mold colonies in peanut surface,lowered the rate of peanut mildew and the relative quantity of Aspergillus spp.,but also reduced the decline of vitality of peanuts and the increasing rate of acid value and the content of aflatoxin B₁ in peanuts.Within the range set in this experiment,the adding amount of MCLCEO was higher,the quality of peanuts was better,the best adding amount of MCLCEO was 0.20%（w/w）.In a word,MCLCEO was able to reduce the colony number of molds on the surface of peanuts and improve the quality of peanuts to a certain extent during the process of storage,which is expected to be regarded as natural anti-mildew agents for peanut storage.