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

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 degrees C. Reverse phase liquid chromatography proves an excellent means of separating isomers. In addition, we have compared two mass spectrometry ionization methods-atmospheric 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 chromatography-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.

Comparison of Procedures for Resveratrol Analysis in Beer: Assessment of Stilbenoids Stability through Wort Fermentation and Beer Aging

“…Very efficient for hop extraction 3 , ethanol:water (80:20, v/v) recovered only 38% of resveratrol from the cartridge. Less hydrophilic solvents, such as pure ethanol with or without a trace of formic acid, emerged as the best compromise.…”

“…Flavonoids, the major constituent of hop polyphenols (1-5%), also derive from malt and adjuncts 4,5 . On the other hand, hop is the only source of prenylchalcones and stilbenoids 3,25,26 . Total trans-stilbenoids concentrations range from 0.5 to 12 mg.kg 1 in hop cones 9,12 and up to 9 mg.kg 1 in hop pellets [10][11][12] .…”

“…In the case of liquid extraction, ethyl acetate is often used 14,32 . The extract is further analyzed by HPLC hyphenated to UV absorption 8,19,21 , fluorescence 17 , or mass spectrometry 3,32 . GC/MS has also been used to determine trans-resveratrol, after derivatization with bis(trimethylsilyl)trifluoroacetamide (BSTFA) 16,18,[22][23][24]29 .…”

Characterization of the methanolic extract of hops using capillary electrophoresis‐electrospray ionization‐mass spectrometry

“…Traditionally, beer was "hopped" by adding dried hop cones (female flowers of the species Humulus lupulus L. which is a dioecious plant of the Cannabacea family, cultivated in most temperate zones of the world for its female inflorescences) to the wort kettle during the boiling step of beer making. The addition of hops was found to improve the quality of the beer as well as impart the characteristic bitter taste, aroma, foam stability, and antimicrobial protection [4] which was eventually to find flavor with consumers [5].…”

“…HPLC MS/MS has been used by some researchers for the determination of resveratrol in hops [4], fumonisin B-1 and B-2 in beer and raw materials of beer [6], bitter acids in a crude hop extract [7,8], 8-prenylnaringenin as a novel phytoestrogen in hops [9], flavonols glycosides [10], xanthohumol, and related prenylflavonoids in hops and beer [11-].…”