ABSTRACT
Grape amino acid content in Chenin blanc is affected by leaf removal and harvest date

Gast?n Guti?rrez-Gamboa1 and Erna Blancquaert2*
 
‘Chenin blanc’ is a key grape (Vitis vinifera L. subsp. vinifera) variety in the South African wine industry, and its quality is influenced by some viticultural practices, including leaf removal and harvest time. This study aimed to evaluate the effects of leaf removal and harvest date on physicochemical parameters and amino acid content of ‘Chenin blanc’ grapes. The trial was conducted in a commercial vineyard in Stellenbosch, South Africa, during the 2018-2019 season. The results showed that leaf removal and harvest date did not affect ‘Chenin blanc’ berry weight. Leaf removal significantly increased the concentration of several amino acids, including isoleucine, leucine, alanine, phenylalanine, and tryptophan. Grapes harvested at the stage of berries harvest-ripe according to Eichhorn and Lorenz scale (E-L 38) + 18 d had higher soluble solids (23.63 °Brix) compared to those harvested at E-L 38 (21.15 °Brix), and leaf removal resulted in increased soluble solids (23.28 to 21.50 °Brix) compared to control. Succinic acid content was reduced in the leaf removal treatment, and total acidity was lower in grapes with leaf removal (4.85 to 7.56 g L-1). The interaction between leaf removal and harvest time significantly affected the amino acid content. Grapes harvested at E-L 38 + 18 d from vines subjected to leaf removal showed high contents of several amino acids, especially phenylalanine and tryptophan (14.47 to 10.46 and 4.50 to 3.11 mg L-1, respectively). These findings suggest that both leaf removal and the timing of harvest contribute to the N composition of the grapes. The optimal harvest timing at around 25 °Brix aligns with the concept of nitrogenous maturity, and further supporting information is needed to precise vineyard management to enhance wine quality.
Keywords: Defoliation, phenylalanine, sugar maturity, vine microclimate, Vitis vinifera subsp.vinifera, wine.
1Instituto de Investigaciones Agropecuarias, INIA Carillanca, Temuco, Chile.
2Stellenbosch University, South African Grape and Wine Research Institute, Stellenbosch 7600, South Africa.
*Corresponding author (ewitbooi@sun.ac.za).