Ultrasound-assisted extraction of amino acids from grapes

• UAE allows for the extraction of amino acids from grapes in 6 min.
• Water at 70 °C was the best extraction solvent.
• UAE was a suitable method for its application in grapes through the ripening period.

Recent cultivar techniques on vineyards can have a marked influence on the final nitrogen content of grapes, specifically individual amino acid contents. Furthermore, individual amino acid contents in grapes are related to the final aromatic composition of wines.A new ultrasound-assisted method for the extraction of amino acids from grapes has been developed. Several extraction variables, including solvent (water/ethanol mixtures), solvent pH (2–7), temperature (10–70 °C), ultrasonic power (20–70%) and ultrasonic frequency (0.2–1.0 s−1), were optimized to guarantee full recovery of the amino acids from grapes. An experimental design was employed to optimize the extraction parameters. The surface response methodology was used to evaluate the effects of the extraction variables. The analytical properties of the new method were established, including limit of detection (average value 1.4 mmol kg−1), limit of quantification (average value 2.6 mmol kg−1), repeatability (average RSD = 12.9%) and reproducibility (average RSD = 15.7%). Finally, the new method was applied to three cultivars of white grape throughout the ripening period.