Yoshimasa Taniguchi (1), Yuji Kaneko (2), Mikio Katayama (2), Yasuji Kawachi (2), Fumitoshi Manabe (3); (1) Central Laboratories for Key Technologies, Kirin Company, Limited, Yokohama, Japan; (2) Research Laboratories for Health Science & Food Technologies, Kirin Company, Limited, Yokohama, Japan; (3) Research Laboratories for Beverage Technologies, Kirin Company, Limited, Yokohama, Japan
Isomerized hop extracts and chemically modified reduced hop extracts that contain highly pure iso-alpha-acids and reduced iso-alpha-acids, respectively, have been widely used for brewing to add bitterness and improve beer quality. These components have also received considerable attention because of their multiple bioactivities. However, their intense and sharp bitterness make it very challenging for them to exert potential benefits. Humulinic acids (HAs), which are derived from alkaline hydrolysis of iso-alpha-acids, have been reported to be strongly less or non-bitter. In this study, we aimed to develop a novel hop extract comprised of HAs. HAs were quantitatively generated with fatty acid by-products, 4-mehyl-3-pentenoic acid and 4-methyl-2-pentenoic acid, by alkaline hydrolysis of isomerized hop extract. The fatty acids had a very unpleasant odor and made it difficult to use the hydrolyzed extract as a food additive. A very simple and effective method to separate HAs from the fatty acids was successfully developed. Addition of a divalent metal ion, such as magnesium, to the hydrolyzed extract formed precipitate of HAs, and the fatty acids could be completely removed by filtration. Washing the HA–metal ion complex with acidic water yielded a yellow solid of free HAs. An aqueous solution of highly pure, concentrated potassium salt of HAs could be obtained by addition of potassium hydroxide and/or potassium carbonate. The appearance of the obtained HA extract was similar to aqueous isomerized hop extract but had markedly reduced bitterness. The stability of the extract was very good, and no degradation of HAs was observed for at least 4 months in an acceleration test at 60°C. Furthermore, HAs in a model beverage solution (pH 4.0) containing the extract were stable during storage for 2 months at 35°C. The less-bitter character and high stability of the developed extract may lead to practical use of the extract to improve beer quality and as a potential bioactive agent.
Yoshimasa Taniguchi graduated from the Department of Agriculture at Kyoto University in Japan in March 2006. He began his career in the Central Laboratories for Key Technologies at Kirin Company, Ltd. in April 2006. He has investigated hop chemistry in the laboratory since 2009.