Xiaotong Lyu1, L. D. ARAUJO1, S.-Y. QUEK1, W. J. DU TOIT2, - P. A. KILMARTIN1
1 School of Chemical Sciences, University of Auckland, New Zealand
2 Institute for Grape and Wine Sciences/Department of Viticulture and Oenology, Stellenbosch University, South Africa
Email contact: xiaotonglv[@]yahoo.com
AIM: This study aims to investigate the effects of different conditions of grape processing or fermentation on the aroma profile of New Zealand white wines.
METHODS: Experiments have been designed to study how glutathione and ascorbic acid impact on the aroma compounds of Sauvignon Blanc and Pinot Gris wines. Attention was also paid to the effectiveness of two gas sparging regimes (oxygen and nitrogen), applied during fermentation, on the removal of reductive sulfur aromas in Sauvignon Blanc wines.
RESULTS: Additions of glutathione to the grape juices increased the levels of polyfunctional mercaptans in the finished wines. The lowest levels of polyfunctional mercaptan compounds were found in the wines with little supplementary antioxidants added. A high level of the joint combination of ascorbic acid and glutathione provided the wines with even higher production of polyfunctional mercaptans. Increasing the amount of elemental sulfur addition to the grape must before pressing led to an increase in the formation of several thiol compounds, including some unwanted reductive compounds. Few changes were observed in the concentrations of aroma compounds when the juices were sparged with nitrogen during fermentation. Additions of oxygen during fermentation led to some decrease in the concentration of polyfunctional mercaptans for the 10 mg/L sulfur additions, but did not significantly remove reductive aroma compounds.
CONCLUSIONS: This study has demonstrated a positive benefit to the formation of polyfunctional mercaptans with passionfruit/ tropical aromas, from additions of glutathione and ascorbic acid at harvest. The oxygen or nitrogen applied during fermentation did not result in the removal of undesirable reductive aroma compounds. Further trials are needed to examine increased oxygen as well as nitrogen dosages during fermentation, and their effects on reductive compounds.
Keywords: Sauvignon Blanc, Pinot Gris, antioxidants, glutathione, ascorbic acid, reductive compounds, oxygen, nitrogen, polyfunctional mercaptans