## 2 SPME-GC/MS Methods
### _\"Foxy Smelling Compounds\" and 3-Alkyl-2-Methoxyprazines in Grape Juice_  
2'-Aminoacetophenone (_o_-AAP) is the main compound identified as the cause of the aging note--the so-called \"hybrid note\", \"foxy-smelling\" or \"American character\"--typical of _V. labruscana_ grapes, even though it was also found in some _V. vinifera_ wines such as Muller-Thurgau, Riesling, and Silvaner [56]. This note is variously described as \"acacia blossom,\" \"naphthalene note,\" \"furniture polish,\" \"fused alcohol,\" and \"damp cloth,\" and causes a considerable number of wine rejections. The formation of _o_-AAP in grape is promoted by several factors, such as reduced nitrogen fertilization in combination with hot and dry summers, and the risk increases in wines made with grapes harvested early. The phytohormone indole-3-acetic acid (IAA) is the principal precursor of _o_-AAP through non-enzymatic processes [57,58]. Also, methyl anthranilate (MA) contributes to the typical foxy taint of wines made with American and wild vine grapes, although it was also found in some _V. vinifera_ white wines in concentrations of up to 0.3 \(\upmu\)g/L [59]. For analysis of _o_-AAP in wine a direct-immersion SPME method by using a DVB/CAR/PDMS fiber and GC/MS, was proposed [60]; instead, analysis of MA in grape juice was performed by using a PDMS fiber [61]. 3-Alkyl-2-methoxypyrazines are present in the grape skin, pulp, and bunch stems. These compounds contribute to the aroma of wines by conferring vegetative, herbaceous, bell pepper, or earthy notes. They are characterized by very low sensory thresholds: for 3-isobutyl-2-methoxypyrazine (IBMP), 3-_sec_-butyl-2-methoxypyrazine (SBMP),and 3-isopropyl-2-methoxypyrazine (IPMP) are between 1 and 2 ng/L in water. The level of IBMP in wine may be 10 times the sensory threshold, whereas SBMP and IPMP are normally comparable to their sensory thresholds [62, 63, 64, 65, 66, 67, 68]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Barrel**} & \multicolumn{2}{c}{**Months of**} & \multicolumn{6}{c}{**Compounds mg/L**} \\  & **Aging** & **Furfural** & **5-Methylfurfural** & **4-Ethylguanicol** & **Eugenol** & **4-Ethylphenol** & **Vanillin** \\ \hline \multirow{4}{*}{Acacia} & 3 & \(0.02\pm 0.01\) & \(0.03\pm 0.01\) & \(2.24\pm 0.21\) & \(0.009\pm 0.001\) & \(0.67\pm 0.07\) & \(0.09\pm 0.03\) \\  & 6 & \(0.04\pm 0.01\) & \(0.03\pm 0.01\) & \(2.94\pm 0.14\) & \(0.015\pm 0.001\) & \(0.92\pm 0.08\) & \(0.16\pm 0.01\) \\  & 9 & \(0.03\pm 0.01\) & \(0.03\pm 0.01\) & \(3.25\pm 0.67\) & \(0.021\pm 0.005\) & \(1.29\pm 0.41\) & \(0.31\pm 0.07\) \\ \hline \multirow{4}{*}{Cherry} & 3 & nd & nd & \(3.01\pm 1.13\) & \(0.008\pm 0.004\) & \(1.00\pm 0.44\) & \(0.08\pm 0.04\) \\  & 6 & tr & nd & \(3.13\pm 0.26\) & \(0.009\pm 0.001\) & \(1.04\pm 0.06\) & \(0.10\pm 0.01\) \\  & 9 & nd & nd & \(2.79\pm 0.51\) & \(0.007\pm 0.001\) & \(0.86\pm 0.18\) & \(0.12\pm 0.03\) \\ \hline \multirow{4}{*}{Chestnut} & 3 & \(0.04\pm 0.02\) & \(0.03\pm 0.01\) & \(2.53\pm 0.43\) & \(0.024\pm 0.004\) & \(0.84\pm 0.20\) & \(0.45\pm 0.06\) \\  & 6 & \(0.04\pm 0.01\) & \(0.02\pm 0.02\) & \(2.30\pm 0.12\) & \(0.035\pm 0.003\) & \(0.74\pm 0.08\) & \(0.60\pm 0.02\) \\  & 9 & \(0.07\pm 0.01\) & \(0.04\pm 0.01\) & \(1.84\pm 0.18\) & \(0.026\pm 0.002\) & \(0.64\pm 0.04\) & \(0.43\pm 0.03\) \\ \hline \multirow{4}{*}{Mulberry} & 3 & tr & nd & \(2.69\pm 0.75\) & \(0.004\pm 0.001\) & \(1.06\pm 0.26\) & \(0.09\pm 0.03\) \\  & 6 & tr & nd & \(2.72\pm 0.44\) & \(0.006\pm 0.001\) & \(1.27\pm 0.26\) & \(0.08\pm 0.02\) \\  & 9 & tr & tr & \(1.84\pm 0.20\) & \(0.006\pm 0.001\) & \(1.19\pm 0.07\) & \(0.08\pm 0.01\) \\In general, the climate influences the biosynthesis of methoxypyrazines, and higher contents were found in grapes from cooler regions. For example, it was observed that 3-isobutyl-2-methoxypyrazine decreases dramatically during ripening. Methoxypyrazines may be also influenced by the light exposure: in general berries exposed to more sunlight have lower contents [67].