Study On The Release Mechanism Of Essential Oil From Fermented Guava Leaves And Its Nano Preparation

Guava?P.guajava?is a kind of myrtle medicinal plant widely used in traditional folk medicine.Its fruits and leaves have great nutritional and medicinal value.Guava-leaf essential oils have been proved to have the effects of anti Toxoplasma,pain relief,heat stress relief,as well as inhibition of Sclerotinia sclerotiorum and insecticidal and chemotaxis.It is a potential medicinal resource and has commercial potential as a new green pesticide,therefore development of eco-friendly and inexpensive techniques for improving the yield of essential oils is a research hotspot.In this work,the release of essential oils from guava leaves by mixed fermentation of Monascus anka and Bacillus megaterium were investigated.The relationship between the contents of essential oil and the activities of key hydrolases was analyzed to explore the enzymatic mechanism of the release of essential oil from guava leaves by solid-state fermentation.Chitosan was used to embed the essential oil from the guava leaves to improve its instability,poor water solubility,slow and controlled release and in vitro biological activity.It provided a theoretical basis for the development and application of guava-leaf essential oil in different fields.The specific results are as follows:Effect of solid-state fermentation of Monascus anka and Bacillus megaterium on essential oils of guava leaves.There were 33 compounds in the essential oils extracted from the guava leaves produced in Jiangmen,of which the total sesquiterpene content was 92.62%.The fermentation of Monascus anka and Bacillus megaterium would not change the chemical construction of the essential oil components of guava leaves,but Monascus anka would release sesquiterpenes more significantly;Bacillus megaterium would release oxysesquiterpenes and aldehydes and ketones oxyfatty compounds more significantly;the co-fermentation would release the whole essential oil system of guava leaves evenly.On the 10th day of co-fermentation,the total release of guava-leaf essential oils was 6.42 times higher than unfermented samples.On the 10^th day of fermentation,the maximum total release of guava-leaf essential oils was 5514.48?g/g,which was 6.42 times that of the unfermented sample.The effect was superior to ultrasonic,microwave,enzyme-assisted,and supercritical extraction techniques.Enzymatic mechanism of microbial eelease of guava-leaf essential oils.Eleven key hydrolase enzymes secreted by the two strains played an important role in the solid-state fermentation on the release of guava-leaf essential oil.?-glucosidase?r>0.990,p<0.01?,endoglucanase?r>0.993,p<0.01?and xylanase?r>0.800,p<0.01?were the main enzymes that promoted the transformation of non-volatile aromatic glycosides into free volatile compounds.Esterase,protease,lignin degrading enzymes and three cellulases played a key role in destroying cell structure and promoting the release of volatile aromatic compounds.Two peroxidases were responsible for the release of more oxygen-containing sesquiterpenes and oxygen-containing aliphatic compounds by Bacillus megaterium during fermentation.?-galactosidase from Bacillus megaterium was not significantly related to the release of each component because the content was too low.Preparation and characterization of chitosan-fermented guava-leaf essential-oil nanoparticles.In order to reduce the evaporation rate of essential oils,increase the stability and water solubility,chitosan essential oil nanoparticles with hydration particle sizes,actual particle sizes,polydispersity indexes and zeta potentials of 150.8±0.2 nm?218.7±0.6 nm?43.90 nm?92.10 nm?0.231±0.002?0.252±0.002 and 27.4±0.1 m V?30.7±0.1 m V were prepared by using chitosan and sodium tripolyphosphate as entrapment agent.Their entrapment efficiency and drug loading were 9.90%±0.03%?20.30%±0.13%and 4.83%±0.02%?9.01%±0.05%with a delayed and controlled release effect of more than 12 hours.These ensured the basic solution stability of essential oil nanoparticles and the in vivo membrane permeability.Among them,when the mass ratio of chitosan to essential oil was 1:0.50,the nanoparticles had the largest in vitro release of essential oils of 5.30%.Effects of co-fermentation and chitosan nanoparticles entrapment on the in vitro bioactivity of guava-leaf essential oils.After 10-day fermentation,DPPH radical scavenging ability of guava leaf essential oil decreased by 26.15%,but ABTS⁺radical scavenging ability,5-lipoxygenase and tyrosinase inhibition ability increased by 32.66%,18.73%and 7.87%,respectively,the corresponding IC₅₀ reached 21.47±1.95 mg/m L,20.47±2.49 mg/m L,23.21±1.92?g/m L and 107.41±3.48?g/m L.Overall,fermentation can improve the antioxidant and biological activities of the guava leaf essential oils.The embedding of chitosan nanoparticles further increased the four biological activities of guava-leaf essential oils by 1.05,1.27,1.29,and 1.43 times,respectively.