<p>Hop
(<i>Humulus lupulus</i> L) belongs to the
Cannabaceae family and is well-known to be a dioecious, perennial climbing
plant. The common hop is native to temperate climates, but due to its
widespread commercial use in the brewing industry, hop plants are grown
worldwide. The bittering components in hops, especially the a-acids, provide a
pleasant bitterness and characteristic flavors to beer. On their own, a-acids do not
contribute much to beer bitterness but do so after they are converted to iso-a-acids during the
kettle boil step in brewing. b-acids in hops are not as
important as a-acids,
since they only supply about a third of the bittering power as a-acids but are
mostly responsible for hops’ antimicrobial properties. The goal of this study
was to investigate the effects of storage conditions on the degradation rate of
hop constituents. Pelletized hops from two varieties grown in Knightstown, IN
were studied: Cascade (typically used as aroma hops) and Chinook (mostly used
as bittering hops). The impact of storage conditions on hop chemical
constituents, hop storage index (HSI), and color parameters was evaluated at
three storage temperatures (4℃, 25℃, 35<sup>o</sup>C) with hop pellets exposed
to two different gases in headspace (nitrogen or air) for a duration of up to
168 days (4℃ and 25℃) and 70 days (35℃). Hop acids content was determined by
UV/Vis spectrophotometry and HPLC-DAD. Results showed that increased storage
temperature decreased the a-acid concentration in hops. At 4°C and 25°C the loss in a-acids was (14.5 –
23.4%) whereas at 35°C there was a greater
loss in a-acids.
The a-acid
loss between nitrogen flushed and air exposed pellets was not significantly
different (p>0.05) except for Chinook pellets stored at 35°C. b-acids remained
mostly stable for the duration of the study; however, at 35℃ the loss of b-acids over time
became significant for both varieties. HIS values increased over time for both
varieties at 4 and 25<sup>o</sup>C, however, those values remained below the
recommended 0.40 value. At 35<sup>o</sup>C, the HSI values indicated unsuitable
hops for brewing at the end of the study for both varieties. The color
parameters L* and b* remained constant after 168 days at 4 and 25<sup>o</sup>C,
while the a* value and the hue angle showed a significant decrease with time
and increasing temperature. At the conclusion of the study it was demonstrated
that the loss in a-acids
from Cascade pellets at 35℃ was lower than the loss in Chinook, suggesting that
at high temperature the a-acids in cascade were more
stable than those in Chinook.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/13360154 |
| Date | 14 December 2020 |
| Creators | Geraldine Madalitso Tembo (9754958) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Effects_of_storage_conditions_on_alpha_acid_degradation_of_Indiana_Grown_Hops_Humulus_lupulus_/13360154 |
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