| Turmeric is a kind of perennial understory economic plant,and curcumin compounds are the main effective substances in turmeric.While turmeric oil,as by-product in the processing of curcumin,is not bing used properly.Turmeric oil is natural plant essential oil with physiological activities such as antibacterial,anti-inflammatory and antioxidant,but its antibacterial mechanism is not clear,and there are natural defects such as irritating odor and instability,which greatly limit its development and utilization.In this paper,the chemical composition and antibacterial activity of turmeric oil,the preparation process and performance evaluation of turmeric oil liposomes were studied,and the antibacterial mechanism was revealed.The main results were as follows.(1)Chemical composition and antibacterial activity of turmeric oil.Turmeric oil was extracted from turmeric by steam distillation,and the chemicalcomposition and content of turmeric oil were analyzed by gas chromatography-mass spectrometry(GC-MS).Foodborne pathogens such as Escherichia coli,Bacillus subtilis,Listeria erichia and Listeria monocytogenes were screened for antibacterial activity.The results showed that 13 components were identified from turmeric oil,accounting for 89.58%of the total,in which ar-tumerone(37.85%),α-curcumene(15.26%),β-sesquiphellandrene(13.08%),Zingiberene(8.13%),curcuminone(7.49%)and β-bisabolene(3.68%)were the main components.Of the four strains tested,turmeric oil had the most significant effect on Listeria monocytogenes,with bacteriostatic zone of 11.75 mm and minimum inhibitory concentration of 6.25 mL/L,followed by Listeria escherichia,Bacillus subtilis and Escherichia coli.(2)Preparation and properties of turmeric oil liposomes.Turmeric oil liposomes were prepared by the thin film hydration and sonication method.Response surface methodology was used to optimize the preparation process of turmeric liposomes.Further,the morphological structure,particle size,polydispersity index,storage stability,release performance,antibacterial performance and cytotoxicity of turmeric oil liposomes were evaluated.The optimal condition was obtained.When the volume concentration of turmeric oil was 1.2%,the mass ratio of lecithin to cholesterol was 5:1(g/g),and the ultrasonic time was 21 min,the encapsulation efficiency of turmeric oil reached 96%.Turmeric liposomes had a phospholipid bilayer structure with a particle size of 0.896±0.424 μm and polydispersion index(PDI)of 0.44 ± 0.181.The pH remained stable after 14 days of storage at 4℃ and 25℃,respectively.The cumulative release rates of turmeric oil in simulated release solution of 10%ethanol and 50%ethanol were 11.7%and 21.5%,respectively,which showed stable release effect.The release process was in accordance with Ritger-Peppas and first-order release kinetics models,respectively.Furthermore,turmeric oil liposomes had stable inhibitory effect on Listeria monocytogenes,and the inhibition rate was 97.6%at day 4.The suitable concentration of turmeric liposomes should be within 50 mg/mL.(3)Antibacterial mechanism of turmeric oilThe inhibitory mechanism of turmeric oil on Listeria monocytogenes was studied from the cell level.SEM and TEM analysis showed that turmeric oil damaged the cell structure of Listeria monocytogenes seriously.The cells appeared invagination,shrinkage,damage and even holes,and the internal tissue was obviously damaged,leading to the leakage of cell contents.After treatment with turmeric oil,the fatty acid composition of cell membrane of Listeria monocytogenes was changed,the content of saturated fatty acid increased to 3.65%compared with the blank group(2.53%),and the content of unsaturated fatty acid decreased to 0 compared with the blank group(11.95%).Mobility was reduced,resulting in structural damage,rupture,and increased permeability of the membrane.The analysis of protein gel electrophoresis showed that the molecular weight of bacterial proteins in 35-40 KDa,55 KDa,100 KDa and 130 KDa became lighter or even disappeared after 4 hours of treatment with turmeric oil.The bands with molecular weights of 35-55 KDa and 70-130 KDa of bacterial proteins basically disappeared after 16 hours of treatment with turmeric oil,indicating that turmeric oil inhibited the expression of some proteins in bacterial cells,resulting in the failure of cells to reproduce normally.This paper will provide reference for further exploring the chemical composition,antibacterial activity,mechanism and modification technology of natural plant essential oils similar to turmeric oil,as well as theoretical basis for its high-value development and utilization. |
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