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.

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Le fromage fondu est issu de la seconde transformation du lait. Sa fabrication implique le mélange, le chauffage et la texturation de produits laitiers (fromage, beurre et poudres de lait) et non laitiers (agents émulsifiants, acide citrique et chlorure de sodium). Le résultat est un produit homogène, généralement tartinable et à la durée de conservation longue, souvent supérieure à 6 mois. Au cours de la fabrication et du stockage, les réactions d’oxydation des lipides, de caramélisation et de Maillard forment des composés odorants dont certains sont potentiellement indésirables pour la flaveur du produit. Dans le cadre du projet ANR-06-PNRA-023 Réactial, une démarche méthodologique a été mise en place afin : (i) d’identifier les marqueurs réactionnels précurseurs ou responsables des défauts de flaveur observés, (ii) de suivre l’évolution de ces marqueurs au cours des traitements thermiques appliqués, (iii) d’établir un schéma réactionnel observable en vue (iv) de la modélisation et de la prédiction de l’évolution des marqueurs réactionnels et indirectement de l’apparition de défauts de flaveur. Ceci a nécessité la mise au point d’une formulation de matrice de fromage fondu modèle ainsi que l’élaboration d’une cellule de traitement thermique. Différents couplages de chromatographie en phase gazeuse à l’olfactométrie ont été utilisés afin d’identifier les composés odorants. La chromatographie bidimensionnelle systématique couplée à la spectrométrie de masse à temps de vol a permis une semi-quantification des composés traces et ultra-traces tandis que les précurseurs ont été quantifiés par chromatographie liquide haute performance. Les données ainsi obtenues ont permis l’écriture d’un schéma réactionnel observable qui a donné lieu à une modélisation stoechio-cinétique multi-réponses. Un ajustement des données expérimentales par le modèle a pu être réalisé malgré une quantification partielle des différents constituants. / Processed cheese derives from a secondary milk processing step that involves mixing and heating dairy (cheese, butter and milk powders) and non-dairy products (emulsifiers). This processing yields a homogeneous product, usually spreadable, with a shelf-life often longer than 6 months. During processing and storage, lipid oxidation, caramelization and Maillard reactions occur and produce odour-active compounds. Some of them are potentialy involved in the development of odour defects. As part of the ANR-06-PNRA-023 Réactial project, a methodological approach was used in order to (i) identify key compounds responsible for the flavor defects observed, (ii) monitor the evolution of these markers during the heat treatment applied to the cheese matrix, (iii) establish an observable reaction scheme, (iv) model and predict the evolution of these compounds during thermal operations. To do this, a model cheese and its cooking cell were elaborated. Various couplings of gas chromatography with olfactometry were used to identify odorous compounds. Two-dimensional comprehensive chromatography allowed a semi-quantitation of trace and ultra-trace compounds, while precursors were quantitated by high performance liquid chromatography. An observable reaction scheme was extracted from these data and make the multi-response modelling step possible despite a partial quantitation of the volatile compounds.