Strategies for the identification and sensory evaluation of volatile constituents in wine

Abstract

Wine aroma, which stems from complex perceptual and cognitive processes, is initially driven by a multitude of naturally occurring volatile constituents. Its interpretation depends on the characterization of relevant volatile constituents. With large numbers of volatile constituents already identified, the search for unknown volatiles in wine has become increasingly challenging. However, the opportunities to discover unknown volatile compounds contributing to the wine volatilome are still of great interest, as demonstrated by the recent identification of highly odorous trace (µg/L) to ultra-trace (ng/L) volatile compounds in wine. This review provides an overview of both existing strategies and future directions on identifying unknown volatile constituents in wine. Chemical identification, including sample extraction, fractionation, gas chromatography, olfactometry, and mass spectrometry, is comprehensively covered. In addition, this review also focuses on aspects related to sensory-guided wine selection, authentic reference standards, artifacts and interferences, and the evaluation of the sensory significance of discovered wine volatiles. Powerful key volatile odorants present at ultra-trace levels, for which these analytical approaches have been successfully applied, are discussed. Research areas where novel wine volatiles are likely to be identified are pointed out. The importance of perceptual interaction phenomena is emphasized. Finally, future avenues for the exploration of yet unknown wine volatiles by coupling analytical approaches and sensory evaluation are suggested.

Qualitative Screening of Volatile Thiols in Wine by Selective Silver Ion Solid-Phase Extraction with Heart-Cutting Multidimensional Gas Chromatography Mass Spectrometry/Olfactometry

“…The challenges for screening unknown volatile compounds in wine were recently reviewed . Additional analytical difficulties that are associated with trace to ultra-trace odorous volatile thiols further complicate their qualitative screening.…”

“…The challenges for screening unknown volatile compounds in wine were recently reviewed. 14 Additional analytical difficulties that are associated with trace to ultra-trace odorous volatile thiols 4 further complicate their qualitative screening. The classic GC-based methods for screening thiol consisted of lengthy selective extractions with the use of organomercuric compounds.…”

“…Multidimensional GC is a common approach when additional resolution capacity is needed for analyzing trace volatile components in a complex sample. 14,32 Through resolving coeluting components, MDGC has been used to identify a number of unknown volatiles in wines (see the examples reviewed in reference 14 ). In these MDGC applications, the heart-cutting was achieved using mechanical valves 33,34 or connectors.…”

“…6,8,12,13 By comparison, the qualitative screening protocols for which the analytical needs and operations differ from those used for targeted quantitation are less explored in the current literature. 14 The mainstream and currently available methodologies for qualitative screening of volatile thiols involve (i) selective extraction of volatile thiol fractions from wine, followed by (ii) chromatographic separation by gas chromatography (GC) and (iii) detection by MS and olfactometry (O). In such methodologies, the selective isolation of volatile thiols is usually lengthy and is facilitated by the use of organomercuric compounds.…”

“…Subsequently, the knowledge of volatile thiols has been expanded through research dedicated to grape and wine. , Robust chemical analysis of these highly active volatile analytes at trace levels in wine still poses an important challenge . With progress collectively achieved on the selective extraction, − chemical derivatization, − modern chromatography separation coupled with mass spectrometry (MS) detection, and chemical synthesis of stable isotope-labelled analogues, quantitation protocols with applaudable accuracy and robustness for targeted thiols in wine and other matrices have become increasingly available. ,,, By comparison, the qualitative screening protocols for which the analytical needs and operations differ from those used for targeted quantitation are less explored in the current literature …”