Grapevine row orientation, vintage and grape ripeness effect on anthocyanins, flavan-3-ols, flavonols and phenolic acids: I. <i>Vitis vinifera</i> L. cv. Syrah grapes

Abstract

Phenolic concentrations are affected by environmental factors and grape cultivar, as well as viticultural practices, which should be considered when a specific phenolic profile is intended. The effect of microclimate induced by row orientation on phenolic compounds of Vitis vinifera L. cv. Syrah/101-14 Mgt grapes was investigated. Grapes were harvested from four vintages at 22 °Brix, 24 °Brix and 26 °Brix from N-S, E-W, NE-SW and NW-SE orientated grapevine rows. Phenolics were quantified in freeze-dried grape skins using an HPLC method. A vintage effect was only evident for specific individual phenolics for the four vintages. Grapes from NE-SW rows at 22 °Brix had the highest total flavonols and anthocyanins. Catechin was highest in grapes from N-S rows at 24 °Brix, whereas total phenolic acids, caffeic acid and total flavonols were highest from NW-SE rows at 24 °Brix and 26 °Brix. Isoquercetin was highest from NE-SW rows at 22 °Brix and 26 °Brix, whereas kaempferol and quercitrin were highest from E-W rows at 24 °Brix. The majority of phenolics was highest from NW-SE rows at 24 °Brix and 26 °Brix. The results indicate that row orientation affects phenolic development in Syrah grapes, but that vintage has a limited effect on phenolics. Light induced in the fruit zone positively affected the grape phenolic development of NE-SW rows at 22 °Brix and that of NW-SE rows at 24 °Brix and 26 °Brix. However, it is unlikely that a single index can be applied to all growing conditions and grape cultivars. Rows that allow moderate radiation intensity in the canopy (i.e., NE-SW and NW-SE during the day) seem more favourable for the development of phenolics than N-S and E-W rows. The light and berry temperature conditions in the fruit zone resulting from row orientation have the potential for widening the range of Syrah wine styles. In practice, a desirable row orientation may not be applicable to all environments. Management of the fruit zone remains an option for increasing or decreasing grape light exposure, irrespective of row orientation.