2.2.2 Lupulon
Synonyms β-Bitter Acid; β-Lupulic Acid.
Biological Sources The biological sources of lupulon are the same as for humulon given under sections 2.1.1.
Chemical Structure
3, 5-Dihydroxy-2, 6, 6-tris (3-methyl-2-butenyl)-4-(3-methy-1-oxobutyl)-2, 4-cyclohexadien-1-one; (C26H38O4).
Isolation Lupulon may be isolated from the commercial hops Humulus lupulus L. (Moraceae) by the method suggested by Lewis et al.*
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* Lewis et al., J. Clin. Invest., 28, 916 (1949).
Characteristic Features
1. It is obtained as prisms from 90% (v/v) methanol having mp 92-94°C.
2. It possesses a distinct bitter taste especially in alcoholic solutions.
3. It behaves as a monobasic acid.
4. It is perfectly stable in vacuo even upto a temperature of 60°C.
5. It exhibits a slight acid reaction.
6. It is found to be optically inactive.
7. It is freely soluble in ethanol, methanol, hexane, petroleum ether, isooctane; and slightly soluble in either neutral or acidic aqueous solutions.
8. It readily forms a sodium salt which is rapidly soluble in water.
9. The addition of 0.1% solution of ascorbic acid affords a marked and pronounced protective action upon the bacteriostatic activity of lupulon steamed or autoclaved at a concentration of 4 ppm in phosphate buffer at pH 6.5 and 8.5.
Identification Tests
1. Lupulon turns yellow and amorphous in nature within a few days with the development of a characteristic odour.
2. Lupulon on being subjected to oxidation with potassium permanganate solution gives rise to the formation of valerianic acid.
Uses
1. Lupulon contributes exclusively to the bitterness of hops extract and is employed in the manufacture of beer.
2. It possesses the properties of an aromatic bitter and are said to have a sedative activity.
