| With the increasing of people's awareness for food safety in modern society,“eating at eace” has become a primary psychology of mass comsumption.The food safety problem caused by abusing of chemical food preservative is still one of the public concerns.Therefore,developing a green,safe,efficient and nutritious natual preservative just can meet this demand.As an important direction of the natural food preservative,the plant original food preservative has become the focus of food industry based on the advantages of abundant resources,nature,safety,nutritional and healthy properties.This thesis aimed to screen out a preservative with a wide antimicrobial spectrum and an effective antibacterial effect from eight plant resources which can be used as medicine and food by modern extraction technology and detection analysis method.The extraction of antibacterial ingredients,identification,antimicrobial effect and application in food storage and preservation were studied.The primary contents as follows:(1)Eight plant materials,such as Lonicera Japonica Thunb,Chrysanthemum,Sophora japonica,Fructus Schisandrae Chinensis,Folium Isatidis,etc,were used to extract antimicrobial active ingredients.The antimicrobial effect of plant extracts against the harmful micro-organisms in foods were investigated by the Oxford Cup method.Using ethanol as extraction solvent,the antibacterial ingredients were extracted by ultrasonic-assisted reflux extraction method.Tested bacteriostatic effect against some bacteria commonly exist in foods,FSC(Fructus Schisandrae Chinensis)was selected for further study.Using response surface methodology to optimize the extraction process: the optimum extraction conditions were determined as ethanol concentration 80%,ultrasonic extraction time 30 min,and the liquid to solid ratio 8 mL/g,under these conditions the schisantherin A,main antibacterial component in FSC was measured to be 1.05 mg/g.The bacteriostatic circle diameter to Escherichia coli,Staphylococcus aureus,mucormucedo and aspergillus were 26 mm,26 mm,23 mm and 28 mm,respectively,and the antiseptic effect was better than that of chemical preservatives.The MIC(minimal inhibitory concentration)for Staphylococcus aureus and mucormucedo was 1.25 mg/mL,and that for Escherichia coli and aspergillus were 6.25 mg/mL,0.625 mg/mL respectively.The content of schizandrol A,schisantherin A and deoxyschizandrin was 11.07 mg/g,1.28 mg/g,1.02 mg/g respectively measured accurately with HPLC under the optimum conditions.(2)More attention was emphasized on the mechanism of antibacterial action against microbiology by measuring the growth curve,electrical conductivity,the use of sugar and scanning electron microscope(SEM)observation.Bacterial growth curve showed that lignanoid inhibite bacterial growth.In addition,the results showed that one of its antibacterial mechanism was that the cell membrane of bacteria cells was broked,a large number of contents outflowed,and the metabolism was influenced,all these are why FSC ethanol extracts can inhibite pathogenic microorganism.(3)The antibacterial activity of FSC in the food simulation system was further studied,the results showed that the antibacterial effect of FSC ethanol extracts had good stability of the ultrasonic,and was suitable for the application of acidic foods;with the extension of time under normal temperature,the inhibitory effect was gradually weakened;the inhibitory effect of ethanol extract had synergistic effect with glucose;the inhibitory effects against Eescherichia coli and aspergillus increased when added metal ions,but besides Fe3+,the inhibitory effect against staphylococcus aureus weakened and against mucormucedo was not obvious.The effects of different concentrations of NaCl on the antimicrobial activity were different.The lignanoid can delay the deterioration of noodles effectively,and the antiseptic effect was better than that of chemical preservatives.Also,the lignanoid can prolong the acid production time of pickled cabbage,and the preservation effect was better than chemical preservative.FSC antibacterial ingredients have the potential to be developed for natural preservatives and bacterial in hibitor. |
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