Quantitative analysis of 3-alkyl-2-methoxypyrazines in juice and wine using stable isotope labelled internal standard assay

• Published in: Journal of Chromatography A Vol. 1190; no. 1; pp. 294 - 301
• Main Authors: Kotseridis, Y.S., Spink, M., Brindle, I.D., Blake, A.J., Sears, M., Chen, X., Soleas, G., Inglis, D., Pickering, G.J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 09.05.2008; Amsterdam; New York: Elsevier; Elsevier
• Subjects: 3-Alkyl-2-methoxypyrazine; Beverages - analysis; Biological and medical sciences; Cabernet sauvignon; Calibration; Deuterated analogues; deuterium; ethanol; Fermented food industries; food analysis; Food industries; Fundamental and applied biological sciences. Psychology; GC–MS; grape juice; Harmonia axyridis; Headspace solid phase microextraction; isotope dilution technique; isotope labeling; Isotopes; Ladybug taint; Magnetic Resonance Spectroscopy; microextraction; Multicoloured Asian Lady Beetles; odor compounds; pyrazines; Pyrazines - analysis; red wines; Reference Standards; Reproducibility of Results; Sensitivity and Specificity; solid phase extraction; solid phase microextraction; stable isotopes; taint; Vitaceae; Wine; Wine - analysis; Wines and vinegars; Wine; Headspace solid phase microextraction; Deuterated analogues; GC–MS; 3-Alkyl-2-methoxypyrazine; Ladybug taint; Harmonia axyridis; Cabernet sauvignon; Multicoloured Asian Lady Beetles; Deuterium; Chemical analysis; Isotope labelling; Coleoptera; Insecta; Internal standard; Chemical enrichment; Clarifying; Sample preparation; Labelled compound; Quantitative analysis; Trace analysis; Validation; Coupled method; Hydrogen Isotopes; Solid phase microextraction; Gas chromatography; Coccinellidae; 3-Alkyl-2-methoxypyrazine,Wine,Cabernet sauvignon,Headspace solid phase microextraction,GC-MS,Deuterated analogues,Multicoloured Asian Lady Beetles,Harmonia axyridis,Ladybug taint; Arthropoda; Headspace; Invertebrata; Mass spectrometry
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2008.02.088

A solid phase microextraction (HS-SPME)–GC–MS methodology was established for the analysis of 3-alkyl-2-methoxypyrazines (MPs) in wine using a stable isotope dilution assay. The compounds analysed were 3-isobutyl-2-methoxypyrazine (IBMP), 3- sec-butyl-2-methoxypyrazine (SBMP), and 3-isopropyl-2-methoxypyrazine (IPMP) using their respective deuterated analogues ([ 2H 3]-IBMP, [ 2H 3]-SBMP, [ 2H 3]-IPMP) as internal standards, synthesised during this work. A divinylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) fibre was selected for isolation of MPs and the effects of matrix parameters such as pH and ethanol concentration were examined in the development of the method. Best results were obtained at a pH of approximately 6 and with a wine dilution factor of 1:2.5, resulting in an ethanol concentration of approximately 5% (v/v). Relative standard deviations (RSDs) of replicate samples were 5.6–7% for all MPs at 5 ng L −1 and <5% for 15 and 30 ng L −1 samples. The limit of detection was <0.5 ng L −1 in juice and 1–2 ng L −1 in wine. The recovery efficiencies for spiked wine samples were between 99 and 102% for all three MPs. Using this method, we investigated the impact of the Multicoloured Asian Lady Beetle (MALB) on MPs in wine. In red wine fermented with live MALB, IPMP is the most prevalent MP detected, although SBMP concentrations are also increased and IBMP is unchanged from background levels. MALB that have been dead for 1 day before addition to juice can still contribute to elevated SBMP concentrations in wine, but not if they have been dead for 3 days or longer. Clarifying juice prior to fermentation leads to substantially lower IPMP concentration in the subsequent wine when compared with unclarified juice.