Hop (Humulus lupulus L.) is an indispensable raw material in beer brewing because it can provide unique aroma and bitterness to beer products. With growing consumer interests in locally-sourced ingredients and increasing number of microbreweries, hop production is emerging in many non-traditional U.S. growing regions like Virginia (VA). However, the lack of understanding on aroma chemistry of regional hops limited their prosperity. Moreover, suitable postharvest drying and packaging practices for VA hop producers are not available. This dissertation aims to address above issues by investigating the aroma chemistry of VA hops by varieties (Cascade, Chinook), growing locations (Meadowview/Petersburg/Blacksburg, VA), smaller-scale drying practices (oven drying, dehydrator drying, freeze drying) and packaging materials (PA/PE, OPP/Foil/PE, EVOH). Our efforts also extended to the novel application of hop-derived ingredients in non-beer drinks to promote value-added products.
Solid phase microextraction and solvent-assisted flavor evaporation were applied for aroma extraction. Gas chromatography-mass spectrometry-olfactometry was used with stable isotope dilution analysis and standard addition method for accurate quantitation of aroma-active compounds. A total of 33 and 36 aroma-active compounds were identified in all fresh and dried hops, respectively. Geraniol, β-myrcene, linalool, methyl octanoate and trans-α-bergamotene were found to be the predominant compounds. Aroma profiles varied significantly with growing locations for both varieties. Individual aroma contents and total essential oil were the highest in dehydrator-dried hops, indicating the advantage of dehydrator-drying being a suitable practice to retain aroma power in hops for most smaller-scale producers in VA. Most volatile compounds in different packaged dried hops showed decreased concentrations over 8-month storage, but the variation was not statistically significant. Hop essential oil (HEO) microcapsules, manufactured by spray drying using modified starch CAPSUL® as the wall material, showed high flavor retention and controlled aroma release. The addition of HEO microcapsules significantly improved the aroma recovery and stability in hop tea. Our findings enhance the understanding of the aroma chemistry in regional hops as affected by multiple pre- and postharvest factors. The novel non-beer application of HEO was also successfully demonstrated. / Doctor of Philosophy / Hop (Humulus lupulus L.) is an essential raw material in beer brewing because it can provide beer products with unique flavor. With the growing "buy local" trend among consumers in recent years, hop production is moving to many non-traditional growing regions in the U.S. including Virginia. This resulted in an increasing number of local craft breweries operating on a smaller scale across the state. However, the aroma characteristics of Virginia-grown hops are unclear. Specific suggestions related to hop postharvest processing and storage are also unavailable for regional smaller-scale hop producers. Therefore, this study aims to study the aroma characteristics of Virginia-grown hops by varieties, growing locations, smaller-scale drying practices and packaging strategies. The novel non-alcoholic application of hop essential oil (HEO, mixture of many hop aroma compounds) was also demonstrated in hop tea. The results showed that both fresh and dried Virginia hops had a complicated profile of aroma compounds that primarily exhibited typical citrus, woody and fruity attributes. Both Cascade and Chinook varieties harvested from Meadowview showed significantly higher aroma contents than hops harvested from the other two locations in Virginia. Most aroma compounds in hops were better preserved by dehydrator drying than freeze an oven drying. No significant change was observed in aroma compositions from hops packaged in three different materials after storage. Finally, HEO particles with enhanced stability were prepared by engineering approaches, which were finally added to hop tea bags for the evaluation of aroma-intensifying effects and storage stability. The results indicated an overall desirable characteristic for the obtained HEO particles. The addition of HEO particles could significantly enhance the aroma stability of hop tea products during storage. Overall, the findings from this study enable a better understanding of flavor chemistry of regional hops from various origins and demonstrated a successful application of HEO particles as a flavoring agent in non-beer products.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110921 |
| Date | 23 June 2022 |
| Creators | Su, Xueqian |
| Contributors | Food Science and Technology, Yin, Yun, Xu, Yixiang, O'Keefe, Sean F., Hurley, Eldon Kenneth, Rutto, Laban Kipkoriony |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/x-zip-compressed |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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