Effects of agronomical practices on chemical composition of table grapes evaluated by NMR spectroscopy

• Discrimination among table grapes is possible for randomized agronomical practices.
• Inter-vineyard variability shows higher discriminating effect than intra-vineyard.
• Levels of glucose, fructose and arginine are dependent on agronomical practices.
• Organic and conventional table grapes differ in sugars-to-acids ratio.
• Ethanol is a minor metabolite naturally found in fresh table grapes.

Nutritional features of table grapes are the result of a complex combination of human practices with weather and environmental conditions. In the present study, the influence of agronomical practices on the chemical composition of commercial table grapes was studied by simple and fast nuclear magnetic resonance (NMR)-based methods. In particular, variability of grape composition was evaluated considering primary metabolites, the compounds directly involved in growth and development of fruits and reliably detected by NMR spectroscopy. Three case studies of increasing complexity were examined. Primarily, it was found that inter-vineyard composition variability has a greater discriminating effect than intra-vineyard variability. The quantities of glucose, fructose, arginine and ethanol are the most dependent on farming practices. The comparison between organic and conventional productions (cv. Superior Seedless) showed a higher sugar content for the conventional practices, resulting in a higher sugar-to-acid ratio. For cultivars Red Globe and Italia, the factors most affected by farming practices were the glucose-to-fructose ratio and the amounts of arginine and ethanol.