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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