Hop resin components

Liquid Chromatography of Hop Resin Components and Related Substances... 

Authoritative recommendations concerning the nomenclature of hop resin components, published in 1969 [4], defined inter alia ... 

Most of the hop resins contain -di- and p-tri-carbonyl functions which are enolized. It is seldom possible to isolate the individual tautomers but estimates of the relative proportions can be obtained by proton magnetic resonance (PMR) spectroscopy and other physical methods. Irrespective of the major component a tautomeric mixture can react in any form if, for example, a minor tautomer is consumed in a reaction it will be regenerated from the major tautomers, according to the equilibrium, until the reaction is complete. Thus phloroglucinol, the parent of the hop resin, exists almost entirely in the trienol form (17) but can react as cyclohexone-1,3,5 trione (18) to form a trioxime (19). 

The bitter taste of beer is principally due to the iso alpha acids, the transformation products of the alpha-acids which arise during the boiling of the hopped wort. Although there are two major and a number of minor isomers of the alpha-acids, and the relative proportions do vary from variety to variety, it is not certain that these differences have a marked effect on bitterness quality. In general, therefore, the total alpha-acid content is a measure of the bittering potential of the hop. Since the other soft resin components do not themselves contribute to bitterness, there has not been much incentive for studying the non-alpha acid, or beta fraction, of the soft resin. 

Reference has already been made to the broader spectrum of resin components extracted under supercritical conditions. A comparison of HPLC chromatograms (Figure 4.6) shows only minor differences. It has not been determined which of the hard resins contribute to the lead conductance valve, enhancing the apparent efficiency of supercritical CO2 compared with liquid CO2 if this method of analysis is used for evaluation. If both hops and extract are analysed by HPLC, there is no difference in efficiency of extraction between the two media. 

It is remarkable that the biogenesis of the hop resins is almost complete before the formation of essential oil components starts (76,77). The isoprene residues are coupled to terpenes when an excess is present with respect to the biogenesis of the hop bitter acids. 

Technically, the specificity of carbon dioxide in the fluid, and particularly the liquid, states makes it attractive as a solvent for hops. The volatile oil components dissolve readily in CO2 while the alpha acids, as components of the soft resin fraction, are soluble to a useful degree. (These components are soluble in non-polar solvents and carbon dioxide is effectively a non-polar solvent). Also the solubilities in this solvent of unwanted compounds with a molecular weight much in excess of about 400 are much lower than those of the compounds which it is desired to extract. 

The spectrum of hop components that dissolve in supercritical carbon dioxide depends upon the temperature and density of the fluid. Forster, in Germany, has shown that by suitable choice of conditions, extracts can be obtained ranging in composition from a similarity with a liquid CO2 extract, to the inclusion of hard resins and tannins. Figure 4.6 shows a comparison between the compositions of hop extracts from various processes. 

About 1/5 of the dry hop weight consists of lupulin particles. These contain all the important components of hops, the bitter acids and the essential oil. The hop bitter acids comprise the alpha and the beta acids. These are only crystalline in very pure form. As mixtures they present themselves as oils or resins which are soft and soluble in hydrocarbon solvents (soft resins). Through air oxidation the hop bitter acids are transformed into ill-defined products which are not longer soft and soluble in hydrocarbons (hard resins). Hops contain yet other organic and inorganic compounds and mixtures. The composition of hops is presented in Table 1. 

Storage Store in cool, dry, well-ventilated area out of direct sunllghL away from heat/ignitlon sources, away from conoslves Uses Mfg. of ethylbenzene, dodecylbenzene, cyclohexane, phenol, nitrobenzene, chlorobenzene, cumene, maleic anhydride, dyes, medidnals, artificial leather, airplane dopes, lacquers solvent for waxes, resins, oils, paints, pharmaceuticals very minor component of gasoline extraction solvent for modified hop extract for flavoring beer in food-pkg. adhesives Use Level 2 ppm (pharmaceuticals)... 

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