| In this paper,pepper leaves essential oil was extracted by deep eutectic solvent assisted technology combined with microwave assisted distillation.The process of microwave assisted distillation based on deep eutectic solvent was optimized by single factor and response surface,and the chemical composition of pepper leaves essential oil was analyzed by gas chromatography-mass spectrometry(GC-MS).The bacteriostatic effect of pepper leaves essential oil was studied.O/W microemulsion system was used to study the microemulsion system,and the stability and antioxidant activity of the microemulsion system were studied.The main conclusions of this paper are as follows:(1)Different kinds of deep eutectic solvents were used to extract essential oil from pepper leaves.It was found that deep eutectic solvent of choline chloride-urea was the best,and the extraction rate of essential oil was the highest.Pepper leaves essential oil was extracted by microwave-assisted distillation based on deep eutectic solvent.Single factor experiments and response surface optimization of three factors affecting the yield of essential oil,such as liquid-to-material ratio,microwave power and extraction time,were carried out.The results showed that when the ratio of liquid to material was 16:1(mL/g),microwave power was 480W and extraction time was 53 min,the maximum yield of essential oil was 1.42±0.02%.Through the comparative analysis of five different methods of extracting pepper leaves essential oil:distillation(HD),ultrasonic-assisted distillation(UAD),microwave-assisted distillation(MAD),ultrasonic-assisted distillation based on deep eutectic solvent(DES-UAD)and microwave-assisted distillation based on deep eutectic solvent(DES-MAD),it was found that the yield of essential oil from pepper leaves was the highest by microwave assisted distillation based on deep eutectic solvent(DES-MAD).The yield of essential oil extracted by distillation(HD),ultrasound-assisted distillation(UAD),microwave-assisted distillation(MAD)and ultrasound-assisted distillation based on deep eutectic solvent(DES-UAD)increased by 17.48%,6.14%,5.66%and 3.15%,respectively.(2)Gas chromatography-mass spectrometry(GC-MS)was used to detect the chemical constituents of five kinds of pepper leaves essential oils:distillation(HD),ultrasound-assisted distillation(UAD),microwave-assisted distillation(MAD),ultrasound-assisted distillation based on deep eutectic solvents(DES-UAD)and microwave-assisted distillation based on deep eutectic solvents(DES-MAD).It was found that there were 34 common components in five kinds of pepper leaf essential oils,including 18 olefins,11 alcohols,1 aldehydes,1 phenols,1 esters and 2 other compounds.The main components include?-Eiemene,Isospathulenol,?-Cubebene,Caryophyllene,?-Elemene,Germacrene D,Ledene,among which the content of olefins is the highest.It was found that the?-elemene in the essential oils of ultrasound-assisted distillation(DES-UAD)based on deep eutectic solvents and microwave-assisted distillation(DES-MAD)based on deep eutectic solvents were18.53%and 17.52%,respectively.The extraction of essential oil from pepper leaves by deep eutectic solvent-assisted technology increased the content of?-elemene.(3)The bacteriostatic effect of pepper leaves essential oil on four kinds of main food safety bacteria(Escherichia coli,Salmonella typhimurium,Bacillus subtilis and Staphylococcus aureus)was studied by agar diffusion method and double dilution method.The results showed that pepper leaves essential oil had inhibitory effect on all four kinds of bacteria.Among them,the bacteriostatic effect of microwave-assisted distillation based on deep eutectic solvent(DES-MAD)was significantly higher than that of distillation(HD),ultrasonic-assisted distillation(UAD),microwave-assisted distillation(MAD)and ultrasonic-assisted distillation based on deep eutectic solvent(DES-UAD).The bacteriostatic effect of pepper leaf essential oil on Gram-negative bacteria(Escherichia coli and Salmonella typhimurium)was significantly better than that of Gram-positive bacteria(Staphylococcus aureus and Bacillus subtilis).Through bacteriostatic zone test,MIC(minimum inhibitory concentration)and MBC(minimum bactericidal concentration),it was found that five kinds of pepper leaves essential oil had bacteriostatic effect,but the effect was different.Among them,microwave-assisted distillation based on deep eutectic solvent(DES-MAD)had the best bacteriostatic effect on Escherichia coli,and the bacteriostatic zone diameter was 22.41 mm,MIC was 0.25 mg/mL,MBC was 0.5 mg/mL.The effect of essential oil extracted by deep eutectic solvent is more effective.(4)The microemulsion system of pepper leaves essential oil was constructed,and the effects of different surfactants,cosurfactants and K_m factors on the microemulsion were investigated,and the suitable microemulsion components were selected by pseudo-ternary phase diagram to prepare pepper leaves essential oil microemulsion.Finally,the O/W type pepper leaf essential oil microemulsion was prepared with Tween 80 as surfactant,anhydrous ethanol as cosurfactant and 70%deionized water as water phase.Its physical and chemical properties are as follows:electrical conductivity is 250.50±0.5?s/cm,viscosity is 20.76±0.22 m Pa/s,and average particle size is 138.95±1.52 nm.Finally,the antioxidant activity of pepper leaves essential oil and pepper leaves essential oil microemulsion was determined and compared by DPPH,ABTS free radical scavenging ability.The results showed that the antioxidant activity of pepper leaves essential oil microemulsion was significantly better than that of pepper leaves essential oil in aqueous environment. |
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