Survey of 3-Alkyl-2-methoxypyrazine Content of South African Sauvignon Blanc Wines Using a Novel LC−APCI-MS/MS Method

Abstract

An LC-MS/MS method for the trace-level determination of 3-alkyl-2-methoxypyrazines in Sauvignon blanc wines is described. 3-Isobutyl-2-methoxypyrazine (IBMP), 3-isopropyl-2-methoxypyrazine (IPMP) and 3-sec-butyl-2-methoxypyrazine (SBMP) were analyzed by reversed phase liquid chromatography coupled to atmospheric pressure chemical ionization, as electrospray ionization was found to suffer from matrix quenching effects. A sample preparation method involving distillation of wine followed by solvent extraction and sufficient preconcentration was developed. Limits of detection and quantification for all three analytes were 0.03 ng/L and 0.10 ng/L, respectively, making the method more sensitive than gas chromatographic methods. IBMP was found to be the most abundant congener in South African Sauvignon blanc wines, with concentrations varying between 0.40 and 44 ng/L in 575 samples. IPMP and SBMP levels varied from <0.03 to 3.9 and <0.03 to 3.2 ng/L, respectively. Statistical investigation indicated no clear correlation between methoxypyrazine content and either geographical origin or vintage. The method was also successfully applied for the quantitation of IBMP in five additional South African wine varieties, including three red wine cultivars. The developed method represents a powerful new tool for the in-depth investigation of these important wine aroma constituents.

Quantitative Survey of 3-alkyl-2-methoxypyrazines and First Confirmation of 3-ethyl-2-methoxypyrazine in South African Sauvignon blanc Wines

“…Chromatographic analysis was performed as reported previously (Alberts et al, 2009), using a Waters Alliance 2695 liquid chromatograph (Waters Corporation, Milford, U.S.A.) coupled to a Micromass Quattro Premier XE tandem quadrupole mass spectrometric detector (Micromass Limited, Manchester, U.K.). Chromatographic separation was in reversed phase mode, employing a methanol and water gradient and a phenyl hexyl column (Phenomenex Luna, Torrance, U.S.A.) with dimensions 250 x 4.6 mm (3 µm particle size), thermostatted at 40°C.…”

“…We have previously reported a survey on MP levels in South African Sauvignon blanc wines and found levels of IBMP ranging from 0.40 to 44 ng/L (RSD of 102%) in 577 wines, while concentrations of IPMP and SBMP ranged from < 0.03 to 3.9 ng/L and < 0.03 to 3.2 ng/L respectively (Alberts et al, 2009). In the current study, 304 additional Sauvignon blanc wines were analysed.…”

“…The procedure used for the analysis of MPs has been described previously (Alberts et al, 2009). Briefly, 500 mL wine was distilled utilising a 60 cm fractionating column, and the first 100 mL of distillate was collected.…”

“…IBMP is invariably the most abundant congener found in Sauvignon blanc wine, representing approximately 80% of the total, while IPMP and SBMP occur in roughly equal amounts Marais et al, 2004;Alberts et al, 2009). The occurrence of 3-ethyl-2-methoxypyrazine (EMP) in wine has also been reported tentatively (Augustyn et al, 1982;Allen & Lacey, 1998;Sala et al, 2000Sala et al, , 2002, while the possible occurrence of 3-methyl-2-methoxypyrazine (MMP) has been suggested on the basis of a feasible biosynthetic route .…”

“…Malic acid concentration was used together with general wine parameters, such as pH, alcohol content (Alc), total acidity (TA) and volatile acidity (VA), in an attempt to identify the factors that are responsible for the production of varietal-typical Sauvignon blanc wines possessing the vegetative aroma. Moreover, given the limited information on MMP and EMP levels in Sauvignon blanc wines, the liquid chromatography-tandem mass spectrometry (LC-MS/MS) method that was previously reported (Alberts et al, 2009) was adapted to yield firm spectral information for the confirmation of the presence of EMP in these wines, as well as quantitative data on this compound in South African wines for the first time. This method utilises advantages inherent to LC-MS/MS to obtain very low detection limits.…”