Hop as an Interesting Source of Resveratrol for Brewers: Optimization of the Extraction and Quantitative Study by Liquid Chromatography/Atmospheric Pressure Chemical Ionization Tandem Mass Spectrometry

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Abstract
Nowadays, hop is used almost exclusively by brewers for bitterness and flavor. Although hop polyphenols have been widely studied in the past decade for their antioxidant activity in the boiling kettle, very little is known about their real impact on health. The discovery of resveratrol in hop pellets highlights the potential health-promoting effect of moderate beer consumption. Here, we have optimized a quantitative extraction procedure for resveratrol in hop pellets. Preliminary removal of hydrophobic bitter compounds with toluene and cyclohexane at room temperature allows 99% trans-resveratrol recovery by ethanol:water (75:25, v/v) solid/liquid extraction at 60 °C. Reverse phase liquid chromatography proves an excellent means of separating isomers. In addition, we have compared two mass spectrometry ionization methodsatmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI)in both the positive and the negative modes. On the basis of standard additions applied with the optimized extraction procedure and reverse phase high-performance liquid cromatography−APCI(+)−tandem mass spectrometry, it appears that Tomahawk hop pellets (T90, harvest 2002) contain 0.5 ppm trans-resveratrol, 2 ppm trans-piceid, no cis-resveratrol, and 0.9 ppm cis-piceid. Keywords: Hop; extraction; resveratrol; polyphenols; health; HPLC-MS/MS; APCI; ESI