Stable Isotope Dilution Gas Chromatography-Mass Spectrometry for Determination of Methoxypyrazines (“Green” Aroma) in Wine

Abstract

Methoxypyrazines are strikingly potent odorants. 2-Methoxy-3-(2-methylpropyl) pyrazine (1) (isobutylmethoxypyrazine) has an odour threshold of 1–2 ng 1^-1 in water (Buttery et al. 1969a,b; Seifert et al. 1970, 1972) and has been widely used in studies of odorant binding to olfactory mucosa (Pelosi et al. 1982), including isolation of odorant-binding proteins (Bignetti et al. 1985; Pes and Pelosi 1995), and in studies of the response of olfactory neuronal cultures to odorant binding (Ronnett et al. 1991). The aroma of this methoxypyrazine is described as bell pepper-like (Buttery et al. 1969a,b; Seifert et al. 1970, 1972; Parliment and Epstein 1973; Murray and Whitfield 1975; Takken et al. 1975), green (Takken et al. 1975), and slightly musty or leafy (Maga 1989). The methoxypyrazine occurs in the berries of some grape varieties, particularly those of Sauvignon blanc and Cabernet Sauvignon vines, and it is incorporated into the wines of these grape varieties in a concentration that can provide distinctive aroma. Odours described as green are also contributed by other odorants, such as the C₆ alcohols generated by oxidative breakdown of fatty acids during fruit processing. However, isobutylmethoxypyrazine provides an earthy, musty, bell pepper or gooseberry-like aroma that is quite distinct. In some winemaking regions of the world, this distinctive aroma is considered important to the regional style of Sauvignon blanc wines; in others, it is disliked.