2.2.8. Determination of Ethanol and Acetaldehyde

For ethanol and acetaldehyde, 5 g of fresh table grape tissues were homogenized with 10 mL of water and then centrifuged at 5 ◦C and 9000 rpm for 10 min. Five mL of supernatant were placed into 20 mL glass vials and stored at −20 ◦C until analysis according to the method of Mateos et al. [28]. After thawing for 1 h in a water bath at 65 ◦C, 1 mL headspace gas sample was withdrawn and injected into a gas chromatograph (Shimadzu GC-14A, Tokyo, Japan) equipped with a FID detector (150 ◦C). Ethanol and acetaldehyde were identified by co-chromatography with standards and quantified by a calibration curve.

2.2.9. Headspace Solid-Phase Microextraction (HS-SPME) and Gas-Chromatography Mass Spectrometry (GC-MS) Analysis

The extraction of volatile compounds was carried out by HS-SPME using an 85 μm Carboxen/Polydimethylsiloxane fibre (Supelco, Bellefonte, PA, USA) and a GC-MS instrument, according to Piazzolla et al. [6].

After thawing the fruit, and detaching seeds and pedicels, 100 g of fruit tissue were added with 2 g of CaCl2, 20 g of NaCl, 100 μL of internal standard solution (100 ppm

2-methyl pentanol methanolic solution) and homogenized using a commercial blender. The homogenized (8 g) was placed into a 15 mL capped SPME vial and stirred for 20 min, at 40 ◦C. Then, the fibre was exposed for 30 min to the capped vial headspace, manually injected into the GC (splitless mode) and kept for 4 min to allow for desorption of volatile compounds. The separation was achieved on a DB-WAX capillary column (60 m × 250 μm × 0.25 μm, J&W Scientific Inc., Folsom, CA, USA) and the identification by comparison of retention time and mass spectra with pure compounds when available, or with data system library (NIST 02, *p* > 80). All compound concentrations were expressed as μg of 2-methyl pentanol equivalent g<sup>−</sup>1.
