ANALYTICAL METHODS FOR THE DETERMINATION OF PHENOLIC PHYTONUTRIENTS IN FOODS
Location: Food Composition and Methods Development Lab
Title: Identification and quantification of flavanoids of Mexican oregano (Lippia graveolents) by LD-DAD-ESI/MS analysis.
Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 31, 2007
Publication Date: June 11, 2007
Citation: Lin, L., Mukhopadhyay, S., Robbins, R.J., Harnly, J.M. 2007. Indentification and quantification of flavnoids of Mexican oregano (Lippia graveolents) by LD-DAD-ESI/MS analysis. Journal of Food Composition and Analysis, 20:361-369.
Interpretive Summary: Phenolic components in plant-based foods are thought to have protective health protective benefits. We have developed a screening method (i.e. a standardized extraction, separation, and detection method that is applied identically to all foods) that allows us to rapidly identify most peaks in a chromatogram representing the phenolic content of food. When known standard are available, the exact compound can be identified. We have applied the screening method to Mexican oregano, a common herb used in the U.S. From a library of 120 known compounds, we were initially able to positively identify 12 phenolic compounds. Using the absorption and mass spectral data for each of the compounds, we have made tentative identification of an additional 11 compounds. The data from this amalysis were stored in a sample library. We now have data for over 200 samples. Results from the samples and standards can be used to identify compounds in future food materials that are analyzed. Continued analyses of food materials like Mexican oregano will allow us to establish a database of phenolic compounds in foods that will support research to elucidate their health benefits.
LC-DAD-ESI/MS was used to analyze 23 flavonoids in the extract of Mexican oregano (Lippia graveolens H.B.K.), a spice and herb used in the U.S. and Mexico. The identification of luteolin-7-O-glucoside, apigenin 7-O-glucoside, phloridzin, taxifolin, eriodioctyol, scutellarein, luteolin, quercetin, naringenin, pinocembrin and galangin was confirmed by direct comparison with standards. Identification of 6-hydroxyluteolin, its two glycosides (three pentahydroxyflavanone hexosides, scutellarein hexoside, 3-hydroxyphloretin hexoside), and three other flavones, was made by detailed analysis of their UV and mass spectral data. The identification of the flavonoid glycosides was further confirmed through detection of their aglycones following hydrolysis of the samples. The concentration of the identified flavonoids in three samples was also estimated. This is the first report of detection of over 20 flavonoids, including chalcones, in this plant material.