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dc.contributor.authorAllison, Rachel Bianca
dc.description135 pages
dc.description.abstractSulfur-like off-aromas (SLOs) are reportedly responsible for nearly 30% of the faults identified in premium wines in competition. Hydrogen sulfide (H2S, “rotten egg aroma”) is most frequently reported in excess of its sensory threshold (~ 1 µg/L) in wines with SLOs. H2S can be produced during fermentation through several pathways but is sufficiently volatile such that the majority formed during fermentation will be lost to CO2 entrainment. After fermentation, winemakers may attempt to remove H2S by inert gas sparging, aeration to oxidize H2S or other VSCs, or addition of cupric (Cu[II]) salts to form non-volatile complexes. A convenient and inexpensive approach for analysis of H2S in wine samples was developed using common winery laboratory glassware and disposable, colorimetric, gas detection tubes. Excellent linearity is achieved using both proposed methods of operation, the N2 Method and the Aspiration Method. Limits of detection are comparable to those achieved using conventional analytical techniques. Recent work has further established that soluble copper-sulfhydryl complexes can serve as precursors for SLO development during wine storage. Copper-sulfhydryl complexes are disrupted in the presence of strong NaCl brine. The quantity of H2S released in this manner is correlated with H2S formation during bottle storage. The factors affecting the stability of these copper-sulfhydryl complexes and the release of H2S during storage are explored in this work and a brine dilution assay has been optimized for releasing H2S from copper-sulfhydryl complexes. Model and commercial wines were treated with copper, sulfide, and glutathione to form metastable copper-sulfhydryl complexes. In wines prepared with the addition of glutathione along with copper and H2S, up to 4-fold increase in recovery of H2S by brine dilution was achieved, compared to the control. Only a small portion of added H2S could by detected following addition of disulfide bond reducing agent (TCEP) suggesting that most of the unrecovered H2S likely formed more stable copper-sulfhydryl complexes. A growing concern for H2S formation is in canned wines and the phenomenon is credited to the reaction of SO2 in wine with aluminum metal. Evidence suggests this can occur even in the presence of a polymeric liner in the can. Considerable variation is observed in H2S production among canned wines with similar free SO2 concentrations, such that predicting the suitability of a given wine for aluminum packaging remains challenging. The initial development of an accelerated bench-test for predicting H2S formation is described, as well as its validation against real canned wine storage for up to eight months. In accelerated aging, negligible formation of H2S was observed in red wines (<10 µg/L), and up to 65 µg/L of H2S was observed in white and rosé wines, even with the best performing liner. In initial experiments, H2S is best correlated with molecular SO2, but the effects of ethanol content and pH cannot yet be fully decoupled to determine the relative roles of different SO2 species.
dc.rightsAttribution-NonCommercial-NoDerivatives 4.0 International
dc.subjectaluminum cans
dc.subjectflavor chemistry
dc.typedissertation or thesis Science and Technology University of Philosophy D., Food Science and Technology
dc.contributor.chairSacks, Gavin Lavi
dc.contributor.committeeMemberRichardson, Ruth E.
dc.contributor.committeeMemberWorobo, Randy W.

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