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Impact of Lees Content, Nitrogen, and Elemental Sulfur on Volatile Sulfur Compound Formation in Vitis Vinifera L

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Impact of Lees Content, Nitrogen, and Elemental Sulfur on Volatile Sulfur Compound Formation in Vitis Vinifera L AN ABSTRACT OF THE THESIS OF Daniel N. Kraft for the degree of Master of Science in Food Science and Technology presented on August 25, 2015. Title: Impact of Lees Content, Nitrogen, and Elemental Sulfur on Volatile Sulfur Compound Formation in Vitis vinifera L. cv. ‘Pinot noir’ wine Abstract approved:______________________________________________________ James P. Osborne 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. ©Copyright by Daniel N. Kraft August 25, 2015 All Rights Reserved IMPACT OF LEES CONTENT, NITROGEN, AND ELEMENTAL SULFUR ON VOLATILE SULFUR COMPOUND FORMATION IN VITIS VINIFERA L. CV. ‘PINOT NOIR’ WINE by Daniel N. Kraft A THESIS Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented August 25, 2015 Commencement June 2016 Master of Science thesis of Daniel N. Kraft presented on August 25, 2015. APPROVED: _______________________________________________________________________________________________ Major Professor, representing Food Science & Technology _______________________________________________________________________________________________ Head of the Department of Food Science & Technology _______________________________________________________________________________________________ Dean of the Graduate School I understand that my thesis will become a part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. _______________________________________________________________________________________________ Daniel N. Kraft, Author ACKNOWLEDGEMENTS I would first like to thank my advisor Dr. James Osborne for his guidance, patience, flexibility, and knowledge. He has taught me a great amount about winemaking, microbiology, and much more. I am very grateful to have been given the opportunity to work in his lab and further my experience in wine science. Thanks as well to the Oregon Wine Board for providing the funding that made this project possible. Gratitude is also due to Dr. Michael Qian and Qin Zhou for performing all of the GC analysis on volatile sulfur compounds for this project, and to Dr. Jaewoo Choi for his work quantifying glutathione by LC-MS/MS. I would also like to thank Dr. Elizabeth Tomasino for her teaching and assistance and Jeff Clawson for loaning tools. Megan Peltz and Victor Algazzali are due thanks for their work in maintaining the HPLC. Thanks to Scott Robbins, Josh Price, and Bentley Chappell for growing the grapes used in this project. Also, thanks goes out to Stuart Chescheir and Anthony Sereni for assistance with wine production and discussions on the subject, as well as Nadine Skyllingstad for her work measuring elemental sulfur residues. I would also like to recognize my family and companion Maggie Harkins for their unconditional love and support. TABLE OF CONTENTS Page LITERATURE REVIEW……..……………………………………………….……………..….....2 Winemaking………………….………………………………...……………..2 Wine Quality and Aroma…..………………………………...…………..3 Volatile Sulfur Compounds……..………….………..……..…………..5 Sulfate Reduction Sequence.….…………..………..……..………..…6 Factors Leading to the Formation of Volatile Sulfur Compounds….………………………...………..………..……..…………...11 Formation of Volatile Sulfur Post-Fermentation.…….…...….23 The Impact of Lees Content on Volatile Sulfur Compound Formation during aging of Pinot noir wine…….……..……..………………..………….……………......….....29 ABSTRACT……………...……….……………………………………………..29 INTRODUCTION…………….……………………..….……………………..30 MATERIALS AND METHODS……….…………………………………..33 Grapes…………………….…….………………………………..33 Alcoholic Fermentation………….………………………..34 Settling, Storage Conditions, and Sampling…..…...35 Volatile Sulfur Analysis……….……………….……….....36 Amino Acid Analysis….………………..……….…………..38 Glutathione Analysis…….…….……………..……………..39 TABLE OF CONTENTS (Continued) Page Statistical Analysis……………………………………..…….41 RESULTS………………………….……………………………………………..41 Turbidity and YAN…….…………….….…………………...41 Amino Acids...………………………….….…………………..43 Glutathione……….………….….………………………….....45 Volatile Sulfur Compounds..………………………….....47 DISCUSSION……….………….……………………..….……………………..52 CONCLUSIONS……………………...…….…………………………………..60 Impact of Nitrogen and Elemental Sulfur on Volatile Sulfur Compound Formation during and after fermentation……………….…………….……….……....……..….............61 ABSTRACT……………………………………………………………………..61 INTRODUCTION…………….……………………..….……………………..62 MATERIALS AND METHODS…………….……………………………..66 Synthetic Grape Juice Experiment……...…………….66 Fermentation………………………...………………………..68 Hydrogen Sulfide Detection and Yeast Enumeration…………………………………………………...68 Elemental Sulfur and Pinot noir Experiment...…...69 Fermentation…………………………………………….……..70 Volatile Sulfur Analysis…….………….....…….…………..71 TABLE OF CONTENTS (Continued) Page Amino Acid Analysis…..………………..……….……….72 Glutathione Analysis…….…….………………………....74 Wine Elemental Sulfur Analysis…………….……….75 Statistical Analysis………………………………..………76 RESULTS………………………….………………………………………….76 Synthetic Grape Juice Experiment………………....76 Elemental Sulfur and Pinot noir Fermentation.84 DISCUSSION………………………………….………………….………….89 Synthetic Grape Juice Experiment………………....89 Elemental Sulfur and Pinot noir Fermentation.96 CONCLUSIONS…………………..………….…..……………...………….101 GENERAL CONCLUSIONS AND SUMMARY.……………………………………………102 LITERATURE CITED………...……..……………..………………………….……………..….104 APPENDICES………………………………………………………………………………………115 LIST OF FIGURES Figure Page 1.1: Sulfate reduction sequence (SRS) pathway
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