Effect of different foliar nitrogen applications on the must amino acids and glutathione composition in Cabernet Sauvignon vineyard

Abstract

Cabernet Sauvignon is one of the most important winegrape varieties in Chile. However, temperature raise and decreased rainfall due to climate change can lead to grape quality decrease in certain areas. Amino acids are essential as nitrogen source for yeast but also directly affect grape quality serving as precursors of certain volatile compounds that enhance the wine bouquet. Besides, glutathione is an important tripeptide acting as antioxidant, preventing the appearance of browning pigments in must and exerts a protective effect in volatile compounds. Thus, increasing amino acid and glutathione content on grapes plays a crucial role in winemaking. Nitrogen foliar fertilization can be a useful strategy to achieve this aim because of the quick and efficient assimilation of applied products by plants. Therefore, the effect of different foliar nitrogen applications on must amino acid and glutathione composition on a Cabernet Sauvignon vineyard was studied in order to increase the grape quality. Nitrogen treatments applied to the grapevines were urea (Ur), urea plus sulphur (Ur+S), arginine (Arg) and two commercial foliar fertilizers with amino acids on its composition (Basfoliar Algae (BA) and Nutrimyr Thiols (NT)). Two applications of 1 kg N/ha were sprayed first at the beginning of veraison and two weeks later. Must amino acid and glutathione were analyzed by HPLC-DAD. Oenological parameters for each sample were also determined. Commercial nitrogen sprays increased the amount of aspartic acid, glutamic acid, serine, glutamine, alanine and ornithine (NT), whereas BA increased the content of serine, glutamine, threonine, arginine, methionine and proline. Ur+S treatment had a better assimilation than Ur, increasing content of aspartic acid, glutamic acid, serine, glycine and methionine. Arg treatment did not increase amino acid content, however it increased the amount of easily extractable anthocyanins, total anthocyanins and total polyphenol index. Foliar nitrogen applications of Arg, NT and BA increased considerably the glutathione concentration, from 2.62 mg/L in control samples to 26.48, 41.51 and 27.6 mg/L in Arg, NT and BA musts, respectively. These findings have oenological and viticultural interest for improving grape quality by enhancing must amino acid composition in high proline accumulating varieties as Cabernet Sauvignon.