White Muscat grapes and Sauvignon Blanc wines (Vipavska
dolina, Slovenia) were used for this study.
Grape samples of 150 intact berries were carefully sorted and
snipped with scissors at the torus. Crushing and skin damage were
carefully avoided. The berries were transferred into a bag, purged
with nitrogen and crushed manually.
Into the 20 mL graduated tube, 18 mL of ice-cold deoxygenated
methanol was added. After the addition of internal
standard N-acetyl-l-cysteine (8.0 mg L−1), 2 mL of grape juice was
transferred to the tube, purged with nitrogen, made up to the
mark with ice-cold deoxygenated methanol and shaken. Samples
were filtered through 0.45 m Minisart RC 25 filters Sartorious
(Goettingen, Germany), diluted 1:1 with 5 mM sodium acetate
buffer containing 0.1 mM EDTA and immediately analysed by
HPLC.
Wine samples were prepared using the same procedure.