Rotundone in New Zealand Vitis vinifera L. Syrah: Fruit, Fermentation and Functional Food Chemistry

Abstract

Rotundone was identified recently as the sesquiterpene responsible for the potent black pepper aroma in Vitis vinifera L. Syrah grapes and wine. Although the New Zealand wine industry is dominated at present by Sauvignon blanc and Pinot noir, many wineries have chosen to use Syrah as their flagship wine indicating the importance of the cultivar to the country. New Zealand Syrah has become known for producing desirable wines with elevated levels of black pepper aromas, more prominent than in wines from other regions or countries, and was anecdotally variable between vintages and blocks. Thus a need was identified to examine the black pepper aroma in Syrah and determine what vineyard and winery factors may contribute to the levels of rotundone in the final wines and if commercially viable management options were available. To that end, a three-season vineyard investigation took place researching selected viticultural management inputs; fruit exposure, timing of fruit exposure, crop load adjustment in addition to berry ripening stage, vine vegetative vigour level and clonal material. Fruit from the remaining blocks were monitored throughout fermentation in commercial size stainless steel and oak fermenters. In addition single cluster fermentations were conducted from the same fruit. A survey of commercially bottled Syrah wines was conducted from wines produced in New Zealand, France, Australia and The United States of America. Finally, the juice and wine matrix of Syrah was analysed for its functional food qualities and to investigate factors that may prove beneficial for inclusion in the diet. Rotundone was indeed present in New Zealand Syrah at some of the highest values recorded to date. Wines from France also had rotundone levels above the perception threshold, while lower values were seen in wines from The United States of America and Australia. Clonal material was the strongest determining factor of rotundone concentration in Syrah. Strong trends were found with timing of leaf removal, where changes made after veraison were more important than beforehand. Fermentation was shown to extract rotundone more rapidly in the early stages and varied with fruit source. Micro-fermentations were found to produce high levels of rotundone, but also showed a high degree of variability. The juice and wine of Syrah grapes were found to show positive antioxidant activities. Both juice and wine had mild to moderate inhibitory activities against COX-1 and -2 in addition to lipid peroxidation. Furthermore, human tumour cell lines showed moderate levels of inhibition from both Syrah juice and wine. There was no difference between the juice and wine on the basis of tumour type indicating that the biotransformation occurring during fermentation did not alter the functional food quality of Syrah. It has been demonstrated that selected vineyard environmental and management factors, along with fermentation factors, influence the concentration of rotundone in New Zealand Syrah. Syrah has also been identified as containing beneficial functional food components relevant to the human diet. These findings support enhancing the growth and production of Syrah in New Zealand, and the beneficial properties of its chemical profiles.