6个特早熟与早熟荔枝种质果实挥发性化合物的鉴定及香气特征分析

Identification of volatile compounds and analysis of aroma characteristics in litchi fruits of 6 special-early maturing and early maturing germplasms

【目的】探究特早熟与早熟荔枝果实挥发性成分特征及差异,为荔枝栽培、育种、加工等提供参考依据。【方法】基于顶空固相微萃取(HS-SPEM)与气相色谱质谱(GC-MS)联用技术,系统地分析了6个特早熟与早熟荔枝种质成熟果实的挥发性化合物,并运用多元统计方法比较了这两类种质挥发性组分的差异。【结果】共鉴定出103种挥发性组分,10种为共有的化合物、34种为各种质的特有化合物,以单萜类、醇类、醛酮类、酯类及倍半萜为主要成分,其中特早熟种质的挥发性物质种类以醇类、醛酮类及酯类为主,早熟种质挥发性物质则以萜类(单萜及倍半萜)及醇类为主。运用OPLS-DA方法获得上述特早熟-早熟组间的差异代谢物39个,其中下调的化合物包括异戊醇、正辛醇、异戊醛、反-2-辛烯醛、乙酸乙酯、3-甲基-3-丁烯醇乙酸酯、乙酸苄酯、戊酸苄酯、苯甲酸异戊酯、α-筚澄茄油烯、α-古巴烯、异戊酸、十四烷,上调的化合物包括α-蒎烯、月桂烯、α-松油烯、邻伞花烃、(+)-柠檬烯、罗勒烯、(E)-Β-罗勒烯、γ-萜品烯、萜品油烯、别罗勒烯、对-薄荷-1,5,8-三烯、芳樟醇、β-香茅醇甲醚、对伞花烃-8-醇、蒎烯-10-醇、α-松油醇、橙花醇甲醚、香茅醇、异香叶醇、β-柠檬醛、香叶醇、乙酸香叶酯、(E)-β-金合欢烯、1,3-环己二烯、α-姜黄烯、α-姜烯,这些差异代谢产物结合各种质特有的化合物可作为区分上述特早熟-早熟种质的特征性挥发性化合物。结合香气活度值(OAV)筛选出对6个特早熟和早熟荔枝种质香气具有贡献的化合物35种,以香叶醇的OAV值最高;发现1-辛烯-3-醇、乙醛、正己醛、壬醛、左旋玫瑰醚、香叶醇、青叶醛为6个特早熟、早熟荔枝种质所共有的香气化合物,其中左旋玫瑰醚、异戊醇、乙酸乙酯、壬醛及1-辛烯-3-醇是特早熟种质三月红、香蜜早和大新荔共有的特征香气成分,而月桂烯、香叶醇、壬醛、邻伞花烃及1-辛烯-3-醇是早熟种质水东、妃子笑、白糖罂共有的特征香气成分。通过香气特征分析发现特早熟种质香型以果香为主,花香、青植香为辅,早熟种质香型以花香为主,果香、青植香为辅。【结论】综上所述,特早熟及早熟荔枝种质挥发性代谢物具有丰富的多样性,不同熟性及不同种质荔枝果实间的挥发性成分及香气成分存在显著差异,挥发性化合物可作为鉴定不同荔枝种质的指标之一。

【Objective】Litchi germplasm resources are very important for litchi breeding,scientific research,and production.Compared with mid and late maturing germplasms,special-early maturing and early maturing lychee germplasm have smaller proportion of planting area and as maller less number ofvarieties due to their sour and astringent taste.However,due to the early maturity trait,they still have a significant place in the market.Volatile substances affect the flavor quality of fruits.Terpenes are extremely important volatile substances,among them monoterpenes and sesquiterpene have special smell and widely exist in plants.The volatile components are important sources of litchi flavor and resistance.However,there have been a few reports on special-early maturing,early maturing germplasm and wild germplasm of litchi.The purpose of this experiment was to explore the characteristics and differences of volatile components in the fruits of special-early maturing and early maturing litchi,and to provide a reference basis for litchi cultivation,breeding,and processing.【Methods】6 accessions of litchi germplasm were selected and divided into special-early maturing group and early maturing group,namely Xiangmizao,Sanyuehong and Daxinli were in the special-early maturing group,and Feizixiao,Shuidong and Baitangyin in the early maturing group.The volatile compounds in mature fruits were systematically analyzed using headspace solid-phase microextraction(HS-SPEM)combined with gas chromatography-mass spectrometry(GC-MS).Principal component analysis(PCA)and orthogonal partial least squares discriminant analysis(OPLS-DA)were used to predict the stability and reliability of the model.The multivariate statistical analysis was used to screen differential metabolites;Hierarchical clustering analysis was used to analyze the metabolites of each group,and the difference of volatile components between the special-early maturing and early maturing germplasm was compared.【Results】A total of 103 volatile components were identified,of them the monoterpenes,alcohols,aldehyde ketones and sesquiterpene were the main components.The alcohols,aldehyde ketones and lipids were the main volatile components of the special-early germplasm,while the terpenoids(monoterpenes and sesquiterpene)and alcohols were the main volatile components of the early germplasm;Feizixiao and Shuidong had the highest cumulative content of volatile compounds,while Baitangyin,Sanyuehong,Xiangmizao,and Daxinlihad had lower content.It was discovered that 10 volatile components were common compounds(ethanol,1-octen-3-ol,acetaldehyde,hexanal,ethanol,1-octen-3-ol,acetaldehyde,hexanal,trans-2-Hexen,1-nonanal,linalool,citronellol,geraniol,(-)-rose oxide)for all the germplasms and 34 compounds were unique compounds to each of the germplasms.Using the OPLS-DA method,39 differential metabolites were obtained between the special-early maturing group and the early maturing group,among them the downregulated compounds included 3-Methyl-1-butanol,1-Octanol,Isovaleraldehyde,(E)-2-Octenal,Ethyl Acetate,3-methylbut-3-enyl acetate,Benzyl acetate,Benzyl valerate,Isoamyl benzoate,α-Cubebene,α-Copaene,Isovaleric acid,Tetradecane,the upregulated compounds includedα-Pinene,Myrcene,α-Terpinene,o-Cymene,(+)-Dipentene,Ocimene,β-trans-Ocimene,γ-Terpinen,Terpinolene,Allocimene B,p-Mentha-1,5,8-triene,Linalool,β-Citronellol methyl ether,2-(4-Methylphenyl)propan-2-ol,Pinane-10-ol,α-Terpineol,Nerol methyl ether,Citronellol,iso-Geraniol,β-Citral,Geraniol,Geranyl acetate,(E)-beta-Farnesene,ar-Curcumen,α-curcumene,α-Zingiberene.These differential metabolites combined with specific compounds of different germplasms could be employed as characteristic volatile compounds to distinguish the special-early maturing and early maturing germplasm.Based on the aroma activity value(OAV),35 compounds contributing to the aroma of 6 litchi germplasm were screened,including 5 alcohols,9 aldehydes,3 lipids,6 monoterpenes,10 monoterpene oxides,and 2 sulfides.The main compounds were monoterpenes and aldehydes with geraniol having the highest OAV value;18 key aroma components also obtained:geraniol,dimethyl trisulfide,myrcene,3-methyl-1-butanol,iso-Geraniol,1-octen-3-ol,(-)-rose oxide,ethyl acetate,hexanal,1-hexanol,citronellol,1-nonanal,isovaleraldehyde,o-cymene,acetaldehyde,phenethyl alcohol,dimethyl disulfide,and linalool,but there were significant differences among different germplasms.1-octen-3-ol,acetaldehyde,hexanal,1-Nonanal,(-)-rose oxide,iso-Geraniol and trans-2-hexen were the common aroma compounds in the 6 lychee germplasms,while(-)-rose oxid,3-Methyl-1-butanol,ethyl acetate,1-nonanal,and 1-octen-3-ol were key aroma components common in the 3 special-early maturing lychee germplasms,and myrcene,geraniol,1-nonanal,o-cymene and 1-octen-3-ol were key aroma components common in the 3 early maturing lychee germplasms.Through analysis of aroma characteristics,it was found that six litchi germplasms mainly contained 10 aroma types:floral,fruity,green plant,citrus,woody,and green fruit.In addition,some germplasms also had a small amount of vanilla,cream,nut,and sulfur-containing vegetable flavors;The aroma of the special-early maturing germplasm was mainly fruity,supplemented by floral and green plant aromas.The aroma of the early maturing germplasms was mainly floral type,supplemented by fruity and green plant aromas.【Conclusion】In summary,the volatile metabolites of the special-early maturing and early maturing litchi germplasms had rich diversity.There were significant differences in the volatile and aroma components in litchi fruits with different maturity,and volatile compounds could be used as indicators for identifying different litchi germplasms.