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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #235642
Title: Quantification of almond skin polyphenols by liquid chromatography-mass spectrometry

Author
item BOLLING, BRADLEY - TUFTS UNIVERSITY
item Dolnikowski, Gregory
item Blumberg, Jeffrey
item CHEN, C-Y OLIVER - JM USDA HNRCA @ TUFTS

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2009
Publication Date: 5/1/2009
Citation: Bolling, B., Dolnikowski, G., Blumberg, J., Chen, C. 2009. Quantification of Almond Skin Polyphenols by Liquid Chromatography-Mass Spectrometry. Journal of Food Science. 74(4):C326-332.

Interpretive Summary: Almond skins contain a class of naturally-produced chemicals called polyphenols, which are thought to promote health through a number of mechanisms. Particularly, the flavonoid class of chemicals are abundant in extracts of almond skins. Previously, we and others have developed methods which identify and quantify the polyphenols from almond skin. This is important to understand not only the contribution of almond to the polyphenolic and flavonoid content of the diet, but also to understand the variability arising from production, harvest, and processing of almonds. The intent of this research was to develop a sensitive, reliable, and accurate method for quantifying almond skin polyphenols. We compared the polyphenol recovery using hot water blanching and liquid nitrogen blanching as a means for removing the skins from almonds. Hot water blanching followed by extraction recovered more polyphenols than liquid nitrogen blanching using a comparable extraction process. We also found the extraction method changes the polyphenolic profile measured in almond skin extract. Therefore, we conclude that it is important to consider the extraction method when quantifying polyphenols, and that our method is a reliable means to measure polyphenols and flavonoids from almond skins.

Technical Abstract: Reverse phase HPLC coupled to negative mode electrospray ionization (ESI) mass spectrometry (MS) was used to quantify 16 flavonoids and 2 phenolic compounds from almond skin extracts. Calibration curves of standard compounds were run daily and daidzein was used as an internal standard. The inter-day coefficients of variation (CV) of standard curve slopes ranged from 13 to 25% of the mean. On column (OC) limits of detection (LOD) for polyphenols ranged from 0.013 to 1.4 pmol, and flavonoid glycosides had a 7-fold greater sensitivity than aglycones. Limits of quantification were 0.043 to 2.7 pmol OC, with a mean of 0.58 pmol flavonoid OC. Mean inter-day CV of polyphenols in almond skin extract was 6.8% with a range of 4 to 11%, and intra-day CV was 2.4%. Liquid nitrogen (LN2) or hot water (HW) blanching was used to facilitate removal of the almond skins prior to extraction using assisted solvent extraction (ASE) or steeping with acidified aqueous methanol. Recovery of polyphenols was greatest in HW blanched almond extracts with a mean value of 2.1 mg/g skin. ASE and steeping extracted equivalent polyphenols, although ASE of LN2 blanched skins yielded 52% more aglycones and 23% less flavonoid glycosides. However, the extraction methods did not alter flavonoid profile of HW blanched almond skins. The recovery of polyphenolic components that were spiked into almond skins before the steeping extraction was 97% on a mass basis. This LC-MS method presents a reliable means of quantifying almond polyphenols.