Determination of α- and β-acids in hops by liquid chromatography or electromigration techniques: A critical review

Hop plays an essential role in brewing beer and its study and analysis is of paramount importance. - and -acids are considered two of the most important hop components. While -acids are associated with the bitter flavor, -acids have antimicrobial effects. This work aims to critically review the published analytical methods for - and -acids determination in hops employing separation methods in liquid medium: liquid chromatography (LC) and capillary electrophoresis (CE). The types of hop samples, the optimized protocols to extract the hop acids, and the main instrumental conditions for both LC and CE techniques are highlighted and discussed. Specific and critical aspects of the - and β-acids separation by LC and CE and some challenges in this field are raised. Several key aspects discussed in this review may be of practical importance for brewers, whether in the microbrewery or industry and for researchers in the brewing field.

Analysis of pesticide residues in hops and their extraction by liquid CO2 during the production of hop extracts

A method has been developed for analysing pesticide residues in whole hops, hop pellets and hop extracts by GC-MS. Five batches of hop pellets containing nine different pesticides (triadimefon, dicofol, mephosfolan, bupirimate, cyhalothrin, tetradifon, endosulfan, pyrazophos and total bisdithiocarbamates) were extracted with liquid CO2. Pesticide concentrations in the original hop pellets and the extracts were determined. The pesticides were concentrated by the extraction process (concentration factor 1.3-8.3), except for the bisdithiocarbamates, which were not extracted. When the same amount of bitterness was added into the brewing process using liquid CO2 extract as opposed to hop pellets, for most of the pesticides proportionately less pesticide was added. However, for two pesticides (dicofol and triadimefon) corrected residue levels were similar to, or in some cases slightly higher than, those in hop pellets.

Avoidance of trace metal activity with micro-liquid chromatography in the analysis of hop and beer bitter acids

Packed fused-silica columns (250 X 0.32 mm I.D.) or micro-liquid chromatographic (LC) and more usual columns in stainless steel (250 X 4.6 mm I.D.) or "conventional LC" are compared for the quantitation of hop and beer bitter compounds. For the hop alpha- and beta-acids the difference is not significant. A slight preference for micro-LC can be argumented on the fact that this system will more readily show the presence of deoxy-alpha-acids. For the iso-alpha-acids the inert character of micro-LC using packed fused-silica columns is essential for good results. It is believed that the inert character of micro-LC would benefit many other analytical problems of complex natural organic compound mixtures.