Abstract

High Performance Liquid Chromatography (HPLC) has been extensively used in the analysis of hop derived components in beer, but the scope of these methods is limited by the range of attainable reference compounds. The synthesis and purification of a range of relevant components has been described by several authors, but in our laboratory these procedures fail to give compounds of sufficient purity. Modification of published procedures are described for the preparation of humulinic acids, dehydrohumulinic acids, hulupones, and colupulone. These procedures provide facile routes for preparation of these compounds in higher yields than was hitherto reported, and also in sufficient purity for their use as standards in quantitative HPLC analysis. Although bitterness in beer is largely due to iso - a - acids, other compounds such as hulupones are considered to have similar bitter properties. Alternative routes to hulupones using the readily available and cheap 6-acids extracts as starting material are therefore examined. Oxidation of Bacids in the presence of sodium sulphite was established as the most feasible route to these compounds. The structural authenticity of all preparations was confirmed by infra-red, and nuclear magnetic resonance analysis. Purity of the compounds was established using HPLC in conjunction with photodiode array detection. Developed HPLC methods, and synthesised pure reference standards are used in the quantitative analysis of humulinic acids in hop iso-a-acid extracts before, and after acid hydrolysis. HPLC methods are also developed for the quantitative analysis of hulupone formed from the oxidation of B-acids solutions. The stability of all compounds synthesised was investigated so that satisfactory conditions for their long-term storage could be identified.