Impact of lees content, nitrogen, and elemental sulfur on volatile sulfur compound formation in Vitis vinifera L. cv. 'Pinot noir' wine Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/mk61rk66z

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  • One of the most common problems in wine production is the formation of hydrogen sulfide (H₂S) and other volatile sulfur compounds (VSCs), which can mask positive aromas at low concentrations and result in unpleasant aromas such as rotten egg, cabbage, garlic, and rubber at higher concentrations. Despite the large body of work researching formation of H₂S during wine fermentation, it remains a frequent issue. Furthermore, much less is known about the formation of these VSCs during post-fermentation aging and impact of factors such as wine lees composition. In particular, little is known about the role of lees composition on the VSC precursor compounds cysteine, methionine, and glutathione. In addition, while the impact of grape must nitrogen content on H₂S formation has been documented, the effect of nitrogen composition on the formation of VSCs is relatively unknown. This study investigated the role of wine lees quantity and composition on formation of VSCs as well as the impact of nitrogen concentration and composition. The role of elemental sulfur in the formation of VSCs during and after fermentation was also investigated. The impact of wine lees was investigated by fermenting Pinot noir grapes with either a common Pinot noir yeast, Saccharomyces cerevisiae RC212, or a non-H₂S producing yeast S. cerevisiae P1Y2. After fermentation was complete, wines were settled for 0, 24, or 96 hours, resulting in wines with high, medium, or low amounts of lees. Wines were sampled after 0, 14, 30, 60, 90, 180, and 270 days and assessed for VSCs by GC-PFPD and for free amino acids by HPLC-DAD. Glutathione was also assessed after 0 and 30 days by LC-MS/MS. Results showed an increase in methionine and cysteine between 14 and 30 days, which corresponded to an increase in H₂S at the same time. Concentrations of methionine and cysteine increased during aging and were influenced by yeast strain and level of wine lees. Wines produced using P1Y2 contained higher concentrations of methionine and cysteine than wines produced by RC212 at each level of wine lees; higher lees levels also resulted in higher amounts of cysteine and methionine. Increasing levels of methionine and cysteine did not necessarily result in increased amounts of VSCs in the wines. In general, the concentrations of VSCs in the wines were below sensory thresholds. Hydrogen sulfide decreased after the first 30 days of aging, but other VSCs such as methanethiol and dimethyl sulfide persisted at low levels. The influence of concentration and composition of yeast assimilable nitrogen (YAN) was also investigated. Fermentations were performed by either a high H₂S producing Saccharomyces cerevisiae strain (UCD522) or a non-H₂S producing S. cerevisiae strain (P1Y2). YAN was adjusted to high (346 mg/L) and low (112 mg/L) treatments containing mostly primary amino acids; a third treatment was prepared where the majority of the 346 mg/L YAN was derived from diammonium phosphate (DAP). Lead acetate tubes were used to monitor H₂S production during fermentation; wines were lead acetate tubes then assessed for additional VSCs by GC-PFPD. YAN concentration and composition affected H₂S production during fermentation. Treatments fermented by UCD522 with high DAP had increased formation of H₂S late in fermentation and significantly more methyl thioacetate in the wine post-fermentation. In addition to YAN, the presence of elemental sulfur is also known to impact VSCs. Pinot noir was fermented with an addition of 0, 5, or 15 mg/g elemental sulfur. Fermentations were conducted by UCD522 or P1Y2 at 27°C and H2S production was again measured using lead acetate tubes. Wines were assessed for additional VSC by GC-PFPD. Addition of elemental sulfur resulted in H₂S formation during the alcoholic fermentation even with non-H2S yeast. Elemental sulfur increased production of H₂S late in fermentation and resulted in wines that contained higher concentrations of methyl thioacetate post-fermentation. Wines were analyzed for elemental sulfur by HPLC-DAD; almost no elemental sulfur remained in the wines post-fermentation.
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  • description.provenance : Approved for entry into archive by Julie Kurtz(julie.kurtz@oregonstate.edu) on 2015-09-23T16:35:56Z (GMT) No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: bb87e2fb4674c76d0d2e9ed07fbb9c86 (MD5) KraftDanielN2015.pdf: 1804590 bytes, checksum: a40262ca77fb7f26e9ece7bedff74967 (MD5)
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