Flavor Chemistry of Regional Hops (Humulus lupulus L.) and Novel Aroma Application of Hop-derived Products
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.