Extraction,Nano-emulsion Preparation And Antimicrobial Effects Of Coreopsis Tinctoria Nutt.Oleoresin

Coreopsis tinctorial Nutt.(Kunlun Chrysanthemum)is a kind of rare psychrophyte which is rich in natural products with versatile biological activities.The extract of C.tinctorial Nutt.exhibit excellent antioxidant,antibacterial,hypoglycemic,hypotensive and hypolipidemic activities.Previous reports are limited to the characterization and biological activities of flavonoids and polysaccharides from C.tinctorial Nutt..There were few studies focusing on the volatile oils,especially oleoresin.This situation significantly limited the application of C.tinctorial.Based on this,the present thesis extracted C.tinctorial Nutt.oleoresin(CTO)using supercritical fluid extraction(SFE),optimized the extraction conditions by response surface methodology and analyzed the chemical composition of it.In view of the volatilization and poor water solubility of CTO,the present thesis further emulsified CTO to form a CTO nano-emulsion system(CTO-NE),evaluated its antimicrobial activities and offered a glimpse of its antimicrobial mechanism.The main results are as follows:(1)C.tinctorial Nutt.was used to extract oleoresin by supercritical CO₂extraction technology.The extraction conditions were optimized by response surface methodology,and the chemical composition of CTO were analyzed.The antioxidant activity were also determined.The results showed that the optimal extraction process conditions are extraction pressure 27.5 MPa,extraction temperature 45 ^oC,and extraction time 3 h.Under these extraction conditions,the yield of oleoresin was up to3.171±0.019%.Compared with steam distillation extraction,CTO extracted by SFE has more contents,volatile and non-volatile components with antioxidant.(2)C.tinctorial Nutt.oleoresin nano-emulsion was successfully constructed by PIT method.The influence of different emulsifier,HLB and water content on CTO-NE was studied,and the storage performance was also evaluated.The results show that with Span80/Tween80 as mixed emulsifier,the corresponding series of CTO-NE can be prepared at the ratio of CTO:ethanol:emulsifier=1:1:3 in HLB 13.Under these condition,the particle size of CTO-NE with 95%water content is 94.0±9.0 nm,the zeta potential is-42.3±4.6 m V,and the PDI value is 0.185±0.018.It was found that when the water content was 5%-15%,the emulsion was W/O type microemulsion system.When the water content was 20%-35%,the emulsion convert to bi-continuous type.When the water content reached 40%-95%,the emulsion changed from bi-continuous to O/W type.CTO-NE has good storage performance,and maintains good stability in 3 weeks of normal temperature storage.(3)The antimicrobial activities were assayed by inhibition zones,MIC and kinetics of killing analysis against typical Gram-positive bacteria,Gram-negative bacteria and yeast-type fungi,and its rudimentary antibacterial mechanism was explored.The results demonstrated that Emulsification significantly enhanced the antimicrobial activities of CTO.Compared with single CTO,CTO-NE treatment group had larger inhibition zones.CTO and CTO-NE have better inhibitory effects on Gram-positive bacteria and yeast-type fungi than Gram-negative bacteria.The sensitivity of the experimental strains is ranked as follows:B.subtilis>C.albicans>S.aureus>E.coli.With the increase of water content,the antimicrobial effects of nano-emulsion gradually decreased.Further investigation suggested that reducing the surface hydrophobicity of bacterial and fungal cells,destroying the integrity of bacterial and fungal cell membranes and cell walls,and causing leakage of cell contents may be the mechanism of CTO-NE antimicrobial effects.