1. The Revolution of Wine Oxidation Andrew L. Waterhouse Department of Viticulture & Enology University of California, Davis

2. Oxidation History Ancient wines were quickly oxidized  New wine was most valuable Improvement in technology allowed aging for limited time Current technology can make wine almost anaerobically

3. Micro-oxygenation Introduced by Patrick Ducournau Oxygen added at slow rates  1-100 mL O 2 /L wine/month Effects  Increased wine pigments, stable color  Decreased vegetal aroma  Increased fruity aroma What are the Key Reactions in Wine Oxidation?

4. “Well Accepted” Oxidation Steps Oxygen reacts with phenols to yield quinone and hydrogen peroxide Hydrogen peroxide oxidizes ethanol to acetaldehyde

5. Known Oxidation Products Quinones  Thiol adducts  Coupling Products Aldehydes  Acetaldehyde  Glyoxylic Acid (Tartaric Acid product)  Flavonoid coupling

6. Quinone + Thiols

7. Aldehyde Pigment Reactions “D-ring” formation by acetaldehyde and pyruvate

8. Oxygen Reduction Cascade

9. Oxygen Reduction in Wine

10. Fenton Reaction

11. Reactivity of Hydroxyl Radical Extremely reactive  Oxidizes the “first” molecule it encounters Oxidation products are determined by concentration  i.e. Acetaldehyde from ethanol! Antioxidants cannot protect against this oxidation Can acids or sugars also be oxidized?  Acids 6-8 g/L and sugars 1-2 g/L in “dry” wine

12. Fenton Reaction in Model Wine Hydrogen peroxide reacts to convert ethanol to acetaldehyde Acetaldehyde analysis via HPLC of hydrazone Under nitrogen gas

13. Fenton Oxidation of EtOH 100% Conversion of H 2 O 2 to Acetaldehyde?

14. Ethoxyl Radical Recycles Iron

15. Model Wine: Phosphoric Acid Model Wine: Tartaric Acid Model Wine: Tartaric Acid + 4-MeCatechol Effect of Sulfite and Phenolics Phenols are Pro-oxidants?

16. Oxygen is an Antioxidant? Peroxide/Iron Oxidation of Model Wine

17. Oxygen Limits Iron Recycling

18. Wine Minor Components

19. Glycerol Oxidation Two novel oxidation products Not previously reported in wine  Can they affect wine color, etc?  They do slightly darken red wine when added Laurie and Waterhouse, Journal of Agricultural and Food Chemistry, May 2006

20. Glyceraldehyde Bridged Products Laurie et al, JAFC, 54: 9105.

21. Conclusions Oxidation is an important chemical reaction in food/wine preservation Iron catalyzes two key oxidation reactions Control of oxidation requires knowledge of specific reactions and substrates in food/wine

22. Acknowledgements V. Felipe Laurie  Chilean graduate student, returning to Chile this fall, will work at Univ Talca John Daniliewicz  Retired Pfizer chemist in UK Many, many others  Fenton, Singleton, Cheynier, etc California Competitive Grant Program for Research in Viticulture and Enology American Vineyard Foundation

23. Recent Publications Waterhouse, A.L., V.F. Laurie, Oxidation of Wine Phenolics: a Critical Evaluation and Hypothesis. American Journal of Enology and Viticulture, 57: 306-313 (2006). Laurie V.F.; A.L. Waterhouse, Oxidation of Glycerol in the Presence of Hydrogen Peroxide and Iron in Model Solutions and Wine. Potential Effects on Wine Color, Journal of Agricultural and Food Chemistry, 54:4668-4673 (2005). Laurie V.F.; A.L. Waterhouse, Glyceraldehyde Bridging between Flavanols and Malvidin-3- glucoside in Model Solutions, Journal of Agricultural and Food Chemistry, in press.