| Litsea cubeba is an important aromatic plant in Southern China,and its main constituent is Litsea cubeba oil.Litea cubeba oil is not only a kind of food condiment and perfume,but also has antibacterial,insect repellent and other biological activities.Therefore,Litsea cubeba oil has a wide application prospects in food industry,medicine and agriculture.The aim of the paper is to high efficient use of Litsea cubeba resources and development of value-added products.Extraction kinetics model of Litsea cubeba oil was established,and its chemical composition was analyzed.In addition,antimicrobial activity of Litsea cubeba oil,and its application and mechanism in the preservation of fresh food were studied.This work has important theoretical value and application value for the application of Litsea cubeba oil and other plantessential oils in the preservation.(1)Extraction kinetics model of Litsea cubeba oilBased on mass transfer theory and Fick's second law,two extraction kinetic models were established for steam distillation method(SD)and microwave assisted steam distillation method(MASD),and the model of inner diffusion and gas film controlled diffusion were V=V0[1-exp(-kt)]and V=kt,respectively.The cubeba Litsea with different particle sizes was used to extraction of essential oil,and extraction kinetic models parameters of SD method were obtained.When particle size was 3-5 mm and 10?40 mesh,the process was controlled by inner diffusion,and kinetic equations were V=3.28[1-exp(-2.69×10-3t)]and V=3.28[1-exp(-4.48×10-3t)]respectively,and extraction kinetic constant increased with the decrease of particle size.When the particle size was 40?60 mesh,the internal diffusion resistance and the film diffusion resistance can not be ignored.The extraction kinetic models parameters of MASD method were obtained by experimental data fit.When particle size was 3?5 mm and 10?40 mesh,the process was controlled by inner diffusion,and kinetic equations were V=3.28[1-exp(-8.53×10-3t)]and V=3.28[1-exp(-12.10×10-3t)],respectively.When particle size was 40?60 mesh,extraction kinetic equationsof gas film diffusion were V=21.68×10-3t.Extraction process of the Litsea cubeba oil was strengthened by microwave.Extraction kinetic constant of MASD was more than that of SD with same particle size.The obtained kinetic model has good applicability for the extraction of essential oil.(2)The chemical components and content of Litsea cubeba oilChemical components of Litsea cubeba oil extracted by different extraction methods were same,but their content has significantly different.The content of monoterpene compounds in ZCSD-LCO was significantly higher than that in ZCMASD-LCO and ZCUMASD-LCO,but the content of monoterpene oxide in ZCSD-LCO was less than that in ZCMASD-LCO and ZCUMASD-LCO.Monoterpene compounds were transformed to monoterpene oxides under microwave irradiation.The effect of storage time on chemical components and content of Litsea cubeba oil is significant.Content of citral in XXSD-LCO and ZCSD-LCO was 74.07%and 32.77%,respectively.Content of linalool,cineole in ZCSD-LCO was more than that in XXSD-LCO.There were significant differences for components and content of Litsea cubeba oil extracted from different origin Litsea cubeba.Citral content in ESSD-LCO(78.56%)was the highest,followed in XXSD-LCO(74.07%),and then in ASSD-LCO(57.41%)and YZSD-LCO(54.85%).Some chemical components in Litsea cubeba oil has obvious geographical characteristics.(3)The separation of citral in Litsea cubeba oilHigh purity citral was prepared by chemical addition method using RM-?-CD as phase transfer catalyst.The regression model between the citral yield and influence factors was established by Box-Behnken experiments.The regression model was as following:Y=86.60 +2.40A-0.53B-0.31C-5.28A2-3.17B2-2.84C2-1.87AB+1.38AC-1.40BC.Yield and purity of citral were 86.60%and 96.50%respectively under optimum separation conditions of reaction time 3.30 h,catalyst dosage 0.65mol%and reaction temperature 15.0?.(4)Antimicrobial activity of Litsea cubeba oilAntimicrobial activity of Litsea cubeba oil and citral against six kinds of tested strain was investigated by filter paper method.The results showed that Litsea cubeba oil against 6 kinds of tested strain exhibited good antimicrobial activity.The minimum inhibitory concentration(MIC)of XXSD-LCO against Escherichia coli,Staphylococcus aureus,Bacillus subtilis,Aspergillus niger,Rhizopus and Saccharomyces cerevisiae were 3.12,6.25,3.12,1.56,3.12 and 1.56 mg/mL,respectively.The MIC of citral against six kinds of tested strain listed above were 3.12,6.25,3.12,1.56,3.12 and 1.56 mg/mL,respectively.The MIC of XXMASD-LCO against six kinds of tested strain listed above were 6.25,6.25,6.25,3.12,6.25 and 3.12 mg/mL,respectively.The antifungal activity of three samples was better than that of bacteria.After the addition of Litsea cubeba oil,the cell membrane structure of strain was destroyed,and the permeability of the cell membrane increased,therefore,strain growth was inhibited.(5)Fresh-keeping effect of Litsea cubeba oil on pepper and its mechanismFresh-keeping effect of Litsea cubeba oil on pepper and changes of its physiological and biochemical indexes were investigated by fumigation.The fumigation with Litsea cubeba oil could effectively inhibit the decay of pepper during storage.After 30 day storage,the decay rate and decay index of pepper in Litsea cubeba oil group were significantly lower than that of the control group,and the decay rate and decay index of pepper in 1.0 mL Litsea cubeba oil group decreased by 22.5%and 15.0%respectively compared with the control group.After the pepper treated by Litsea cubeba oil,the decrease of nutrients was delayed,and content of TA,Vc and protein of pepper in Litsea cubeba oil group was more than that in the control group.Therefore,the aging and decay of pepper tissue was delayed in Litsea cubeba oil group.The fumigation with Litsea cubeba oil could induce the increase of phenylalanine ammonialyase(PAL)activity of pepper,inhibit the increase of peroxidase(POD)activity,and reduce the increase of malondialdehyde(MDA).Therefore,lignification of cell wall,and synthesis of phenolic compounds and phytoalexins etc were promoted,and membrane lipid peroxidation was delayed in pepper.The fumigation with Litsea cubeba oil could improve resistance of pepper,and extend the shelf life of peppers.However,the fumigation with high dosage Litsea cubeba oil might cause damage to pepper tissue.(6)Fresh-keeping effect of Litsea cubeba oil on fresh meatFresh-keeping effect of 1.0%and 2.0%Litsea cubeba oil on meat was studied.After meat treated with Litsea cubeba oil,the increase of TVB-N value and pH were delayed,and total volatile basic nitroge(TVB-N)value of 2.0%Litsea cubeba oil groupis 45.55%lower than that of the control group after 18 day.The decrease of nutrients in meat treated by Litsea cubeba oil was delayed.The more the dosage of Litsea cubeba oil was used,the more slowlyprotein content decreased.Therefore,the increase of TVB-N value and pH for meat treated by Litsea cubeba oil were slowed by delay of protein degradation.After meat treated with Litsea cubeba oil,the decrease of superoxide dismutase(SOD)activity was inhibited,and the increase of MDA content decreased.SOD activity of 2.0%Litsea cubeba oil group was 46.36%higher than that of the control group after 18 day.Membrane lipid peroxidation of meat treated Litsea cubeba oil for excessive O2-·accumulation was inhibited by delay of the decrease of SOD activity.Therefore,Litsea cubeba oil exhibited good fresh-keeping effect for meat,and extended shelf life of meat.The fresh-keeping effect was related to the dosage of Litsea cubeba oil. |
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