基于超高效液相色谱-四极杆飞行时间质谱的非靶向代谢组学用于不同来源单花蜜的差异分析

不同的蜜源植物具有结构多样的次生代谢产物。该研究以8种不同蜜源单花蜜(洋槐蜜、枣花蜜、荆条蜜、椴树蜜、荞麦蜜、麦卢卡蜜、枸杞蜜、益母草蜜)为研究对象,建立了基于超高效液相色谱-四极杆飞行时间质谱技术(UPLC-Q-TOF-MS^E)的非靶向代谢组学方法,考察了不同蜜源中次生代谢产物的差异。该研究采用固相萃取前处理方法和UPLC-Q-TOF-MS^E方法,获得不同蜜源单花蜜的植物代谢组信息,并构建了多变量统计分析模型,对不同来源的单花蜜进行模式识别和差异分析,发现洋槐蜜、枣花蜜、荆条蜜、椴树蜜、荞麦蜜、麦卢卡蜜相互间存在不同程度的显著差异。结合模型的变量重要性投影、方差分析与最大差异倍数值,根据精确前体离子和碎片离子质量信息检索Chemspider、HMDB数据库,该研究筛选并鉴定出32个代谢差异化合物,其中黄酮类化合物18个、酚酸类化合物7个、苯苷与萜苷类化合物6个、甾体类化合物1个;研究发现麦卢卡蜜和荞麦蜜以黄酮类化合物为主要差异代谢物,荆条蜜中酚酸类化合物为特征性表达,苯苷与萜苷类化合物主要为椴树蜜的特征代谢物。该研究从植物代谢组学角度初步揭示了不同单花蜜的代谢产物差异性以及特征化合物,为基于化学分析技术的蜂蜜溯源识别与质量评价提供了有效的研究策略。

Analysis of differences between unifloral honeys from different botanical origins based on non-targeted metabolomics by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry

Different nectar plants contain various secondary metabolites. Herein, the differences in the contents of endogenous metabolites in honeys from eight botanical origins (i. e., acacia, jujube, vitex, linden, buckwheat, manuka, wolfberry, and motherwort honeys) were investigated by a non-targeted metabolomics-based method. This method involved solid-phase extraction pretreatment and ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS^E). An oasis HLB cartridge was used for the removal of many saccharides. Chromatographic experiments were performed on an HSS T3 column (100 mm×2.1 mm, 1.8 μm) using a mobile phase that consisted of 0.1% (v/v) formic acid in acetonitrile and water. Mass spectrometry was conducted in the positive and negative modes by electrospray ionization (ESI). Metabolic information about the honeys from different botanical origins was acquired using a multivariate statistical analysis model. Principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA) were conducted for pattern recognition and difference analysis. PCA was performed for 10557 and 2706 data variables in the positive and negative ion modes, respectively. The distribution of honeys from different botanical origins was investigated in 88 honey samples. The three principal components exhibited 48.05% and 57.88% of the total variance in positive and negative ion modes, respectively. The samples studied were divided into six different groups on the basis of their botanical origins and metabolic compounds: linden, vitex, buckwheat, manuka, jujube, and acacia honeys. A permutation test (n=200) was conducted to verify the fit of the model. The differential metabolites were screened on the basis of variable importance in project (VIP; >1), analysis of variance (ANOVA; p<0.05), and maximum fold change (>1.5) by using the PLS-DA model. The compounds were identified based on the data retrieved from the Chemspider and HMDB databases according to the quality information of precursor ions and fragment ions. Thirty-two differential metabolites were screened and primarily identified according to the characteristic fragmentation rules of specific structure types and data retrieval, including 18 flavonoids, 7 phenolic acids, 6 phenyl and terpenoid glycosides, and 1 steroid. Various flavonoids in buckwheat and manuka honeys, such as quercetin, sakuranetin, 7-hydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one, 5,7-dihydroxy-2-(3-methoxyphenyl)-4H-chromen-4-one, luteolin-7-methyl ether, and pollenitin, were found. In buckwheat honey, the contents of 3-methoxy-2-(4-methylbenzoyl)-4H-chromen-4-one, 2-hydroxy-3,4-diphenylpentanedioic acid, 3'-methoxydihydroformononetin, phenylpyruvic acid, 2-O-p-coumaroyltartronic acid, 2-(3-hydroxy-4,5-dimethoxyphenyl)-4H-chromen-4-one, 7-hydroxy-6-methoxy-3-(4-methoxyphenyl)-4H-chromen-4-one, 4-[(2E)-3-(4-hydroxyphenyl)prop-2-en-1-yl]-3-methoxyphenol, and 7-hydroxy-5-methoxyflavan were the highest; these compounds are the characteristic metabolites of buckwheat honey. In addition, manuka honey possessed the highest contents of gnaphaliin and galangin 3-methyl ether. Moreover, linden honey contained the characteristic phenyl glycosides of (S)-multifidol 2-[apiosyl-(1➝6)-glucoside], 2-phenylethyl-β-D-glucopyranoside, benzyl O-[arabinofuranosyl-(1➝6)-glucoside], crosatoside B, and terpenoid glycosides of isopentyl gentiobioside and 6-O-oleuropeoylsucrose. Vitex honey was found to be rich in quinic acid derivatives such as caffeoyl-3-O-feruloyl-quinic acid/1-feruloyl-5-caffeoylquinic acid, 3-O-caffeoyl-4-O-methyl-quinic acid/3-feruloylquinic acid, and 3-O-caffeoyl-1-O-methyl-quinic acid, in addition to the flavonoids of vitexin, namely, 6″-(3-hydroxy-3-methylglutarate) and apigenin-7-[galactosyl-(1➝4)-mannoside]. Moreover, ponasteroside A was a characteristic marker of jujube honey, and the contents of 6-C-fucosylluteolin and kaempferol 3-(2″-rhamnosylrutinoside) were the highest in acacia honey. In conclusion, the method based on non-targeted metabolomics involving UPLC-Q-TOF-MS^E for different unifloral honeys was found to be fast, effective, specific, and accurate. The differences in metabolite contents and the characteristic compounds in various unifloral honeys were preliminarily illustrated. This study provides an effective analytical strategy for honey traceability and quality analysis of unifloral honey.