| Betula alnoides Buch-Ham.Ex D.Don is a valuable broad-leaved tree species naturally distributed in Southeast Asia,South Asia and south China.It has perfect performance in wood property,and its wood can be used to make wood floor,high-grade furniture and so on,with high economic value.Its barks have high medicinal value,and they can be used to treat colds,postpartum pain,and digestive and orthopedic diseases.It is shown in the practice that the barks of B.alnoides have heavily aromatic flavour,and can be used to extract essential oils,which are of biological activities such as bacteriostasis,antioxidant,anticancer effects,etc.It is thus important for exploitation and utilization of medicinal plant resources to study on chemical composition of essential oils from B.alnoides barls.Up to now,the area of B alnoides plantations has exceeded200,000 ha in China.In order to utilize abandoned bark resources in the management(such as thinning and cutting)and processing and utilization of B alnoides plantations,in the present study extraction techniques were optimized for essential oil from B alnoides barks,and the trees with a series of ages were sampled to carry out extraction and volatilization of bark essential oil.and the trees with a series of ages were sampled to carry out extraction and volatilization of bark essential oil.Dynamical changes in the yield and composition(types and contents of chemical components)of bark essential oil were then analyzed along with tree age.Five excellent provenances were selected to extract essential oil from barks in different stem sections(stem height),comparative analysis on essential oil yield and composition of essential oil was conducted to reveal variation of these traits among the provenances.These essential oils were further used to conduct antibacterial experiments to prove the difference in antibacterial activity of essential oils among trees with different ages as well as among provenances.The objectives of the present study was to determine preliminarily the best age for harvesting B alnoides barks,to screen out elite B alnoides germplasms with high bark essential oil yield and high application value,and therefore to provide technical support for reasonable exploitation and utilization of B.alnoides bark.The main conclusions were listed as follows:(1)Single-factor and orthogonal experiments of hydrodistillation were conducted in succession so as to optimize technique for extraction of essential oil from B alnoides barks taking particle size after smashing,extracting time and ratio of solid to liquid into consideration.The results showed that yield of essential oil from B alnoides barks was affected significantly by these three factors,especially by particle size.The optimized technical condition was determined as particle of 80 meshes,extracting 180 min and the solid to liquid ratio of 1:5,and the oil yield was 0.076% under these conditions.The findings will provide technical support for comprehensive development and utilization of B.alnoides.(2)Stem and branch barks were collected from B.alnoides trees(Guangxi Pingxiang provenance)of 11,21,29 and 40 years old,and their essential oils were extracted using the optimized method developed aboved.Gas chromatography-mass spectrometry(GC-MS)was then applied to separate volatile components,and their relative contents were calculated using the peak area normalization method combined with artificial parsing computer-aided automatic retrieval system.With the increase of tree age,the extraction rate of essential oil from stem barks of B.alnoides decreased from 0.08% for 11-year-old trees to 0.02% for 40-year-old ones.The extraction rate of essential oil from branch barks of 11-year-old and 21-year-old trees were the highest,both above 0.09%,and that for 40-year-old was the lowest(0.03%).A total of 19 volatile components were identified by GC-MS,including 7 esters,6 alcohols,3 hydrocarbones,2phenols and 1 ketone.15 constituents were identified from stem barks and 14 from branch barks.The main constituents of the essential oils of stem and branch barks were all methyl salicylate(96.44% and 98.00%),linalool(2.16% and 0.41%)and benzoic acid,2-hydroxy-,ethylester(0.96% and 0.53%).The other common constituents for both barks were ethyl2-(5-methyl-5-vinyltetrahydrofuran-2-yl)propan-2-yl carbonate,eucalyptol,terpinen-4-ol and(+)-2-bornanone.The number of volatile components in essential oils from stem bark increased gradually from 4 compounds for 11-year-old trees to 6 compounds for 40-year-old trees,while there was no significant difference in those from branch barks between trees with different ages.The contents of essential oils in B.alnoides barks were significantly correlated with tree ages and tree parts.The volatile components were mainly esters.In particular,the relative content of methyl salicylate was high up to above 96 %,while it was not obviously diffed between tree ages as well as tree parts.(3)Essential oils were extracted from B.alnoides barks for trees of five provenances,including Pingxiang in Guangxi(P),Tengchong in Yunnan(G),Baise in Guangxi(V),Shuangjiang in Yunnan(M),and Ruili in Yunnan(I).For each tree,stem was divided into 5sections according to heights(0-1.3 m,1.3-5.3 m,5.3-9.3 m,9.3-13.3 m,13.3-17.3 m),and barks were collected in each section sepatately.The volatile components of essential oil were identified by GC-MS technology.The oil yield increased with increase of stem height.For example,the oil rate increased from 0.044% and 0.048% at section 0-1.3 m to 0.075% and 0.073% of section13.3-17.3 m for Provenances M and I.The oil yield differed obviously among provenances at the same height.The oil yield of provenance G at 0-1.3 m and 1.3-5.3 m is significantly higher than those of provenances M,V and I,while significant difference was absent between it and provenance P.For section 9.3-13.3 m and 13.3-7.3 m,no significant difference was observed in oil yield among five provenances.A total of 19 compounds were in the bark essential oils of all5 provenances,including six olefins,five esters,five alcohols,two ketones,and one phenol.14,17,12,12,11 volatile components were identified from provenances G,M,I,P and V,respectively.The main components were methyl salicylate,linalool,eudesmol,and their relative contents were 91.72-99.01%,0.11-2.62%,and 0.15-1.24%,respectively.For the same provenance,the content of methyl salicylate gradually increased while the contents of linalool and eudesmol decreased with increasing stem height,.18,11,12,9,11 compounds were identified sections of 0-1.3 m,1.3-5.3 m,5.3-9.3 m,9.3-13.3 m and 13.3-17.3 m for all five provenances.At the same section,the relative content of volatile components differed considerably among provenances.The relative content of methyl salicylate,the main component of provenance M,was the lowest at 0-1.3 m.In the 1.3-5.3 m section,the relative contents of linalool in provenances M and P were 2.62% and 1.14%,respectively,which was significantly higher than those in other stem sections(height).(4)Four strains of Monilia albican,Salmonella typhimurium,Escherichia coli and Staphylococcus aureus were used to test the bacteriostatic properties of the bark essential oils of birch trees with different ages as well asfrom different provenances by filter paper method.The results showed that the antibacterial effect of the essential oils were significantly correlated with tree ages.With the increase of tree age,bacteriostatic effect of essential oil on Monilia albican and S typhimurium declined,and the relevant diameter of inhibition zone for bark essential oils from 40-year-old trees were 6.45% and 11.52% lower than those from 11-year-old trees,while the bacteriostatic effect on Escherichia coli and S aureus increased,and the relevant diameter inhibition zone for 40-year-old trees were 24.27% and 5.25% larger than those for 11-year-od trees.The average diameter of inhibition zone for Monilia albican was the largest(9.63 mm).The anti-bacterial effects of bark essential oils on the four strains were significantly different among five B.alnoides provenances.The antibacterial effects on M albican and S aureus were better than those on E coli and S typhimurium.The bacteriostatic effect of provenance M on M albican was 18.50%,12.42% and 5.07% better higher than those of provenance V,I and G,,respectively,while significant difference was absent between it and provenance P.The present study selected the optimized technical condition for extraction of essential oil from B alnoides barks,which was particle of 80 meshes,extracting 180 min and the solid to liquid ratio of 1:5,and the oil yield was 0.076% under these conditions;found out that the extraction rate of essential oil from stem barks of B.alnoides decreased with the increase of tree age,whilst there was no significant difference in those from branch barks;explored the effects of 5 provenances with different sections on the yield and compound content of essential oils,with which the oil yield differed obviously among provenances at the same section and increased with the increment of stem height,the relative content of volatile components differed considerably among provenances with the same section;and tested the bacteriostatic properties of the essential oil from B alnoides barks on four tested strains.The results can lay a foundation for the further development of essential oil from B alnoides barks. |
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