A-73: Variation of bitter substances from hop pellets during storage

C. Liu (1), Y. Zhou (1), Y. LI (1), X. Yin (2), Q. Li (1); (1) Jiangnan University, Wuxi, China; (2) Cargill Malt, Wayzata, MN, U.S.A.

Poster

The hop is regarded as an essential ingredient in the beer brewing industry, which can contribute bitterness, foam, flavor, mouthfeel, antimicrobial activity, and flavor stability to beer. The variation of alpha-acids, beta-acids, and iso-alpha-acids from hop pellets produced in China during storage was analyzed by reverse-phase high-performance liquid chromatography (RP-HPLC) in this study. Results showed that the content of alpha-acids and beta-acids decreased constantly during storage, wherein the variation of humulone content was the most significant. The degradation rate of bitter substances in different hop varieties exhibited an obvious difference. For example, the content of alpha-acids in Tsingdao Flower, Marco Polo, Columbus, and mixed pellets decreased by 8.05, 12.24, 12.02, and 5.12%, respectively, after aging for 6 days at 50°C; decreased by 3.80, 9.99, 8.35, and 4.86%, respectively, after aging for 12 weeks at 30°C; and decreased by 1.42, 5.41, 3.64, and 2.44%, respectively, after storage for 8 months at –4°C. These differences probably could be attributed to the distribution of hop components, such as the ratio of alpha-acids to beta-acids, the ratio of humulones to adhumulones, and the content of cohumulones. Iso-alpha-acids could be determined in the early period of hop storage, with a lower content. Meanwhile, the content of iso-alpha-acids first increased with the extension of storage time. However, when the ratio of iso-alpha-acids to alpha-acids content was up to about 0.17, the content of iso-alpha-acids decreased slightly. Main components of aging hops were analyzed by ultra-performance liquid chromatography (UPLC). Oxidation and reduction of alpha-acids and beta-acids were well explained by the formation of iso-alpha-acids and some derivative oxides like humulinone and hulupone. Furthermore, the research showed that the variation of hop freshness was well described by the hop freshness index (HFI). Compared with the hop storage index (HSI) and hop degradation degree, the value of HFI could evaluate hop freshness with different varieties more accurately. This new indicator was used to evaluate the freshness of aging hops caused by different temperature, which displayed a good prospect for application.

Yongxian Li received a master’s degree in fermentation engineering from Jiangnan University, Wuxi, China. She began employment with Jiangnan University in 1985. She is now working as an assistant teacher in the Lab of Brewing Science and Technology in the School of Biotechnology. Since 2008, she has functioned as a senior engineer in Jiangnan University.

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