On-line monitoring of volatile organic compounds at pptv levels by means of proton-transfer-reaction mass spectrometry (PTR-MS) medical applications, food control and environmental research

The commercial storage of fruits, vegetables, and florist and nursery stocks

Applications of solid-phase microextraction in food analysis.

Wine is a highly complex mixture of compounds which largely define its appearance, aroma, flavour and mouth-feel properties. The compounds responsible for those attributes have been derived in turn from three major sources, viz. grapes, microbes and, when used, wood (most commonly, oak). The grape-derived compounds provide varietal distinction in addition to giving wine its basic structure. Thus, the floral monoterpenes largely define Muscat-related wines and the fruity volatile thiols define Sauvignon-related wines; the grape acids and tannins, together with alcohol, contribute the palate and mouth-feel properties. Yeast fermentation of sugars not only produces ethanol and carbon dioxide but a range of minor but sensorially important volatile metabolites which gives wine its vinous character. These volatile metabolites, which comprise esters, higher alcohols, carbonyls, volatile fatty acids and sulfur compounds, are derived from sugar and amino acid metabolism. The malolactic fermentation, when needed, not only provides deacidification, but can enhance the flavour profile.

The aroma and flavour profile of wine is the result of an almost infinite number of variations in production, whether in the vineyard or the winery. In addition to the obvious, such as the grapes selected, the winemaker employs a variety of techniques and tools to produce wines with specific flavour profiles. One of these tools is the choice of microorganism to conduct fermentation. During alcoholic fermentation, the wine yeast Saccharomyces cerevisiae brings forth the major changes between grape must and wine: modifying aroma, flavour, mouth-feel, colour and chemical complexity. The wine bacterium Oenococcus oeni adds its contribution to wines that undergo malolactic fermentation. Thus flavour-active yeasts and bacterial strains can produce desirable sensory results by helping to extract compounds from the solids in grape must, by modifying grape-derived molecules and by producing flavour-active metabolites. This article reviews some of the most important flavour compounds found in wine, and their microbiological origin.

Yeast and bacterial modulation of wine aroma and flavour

Fifty-two young monovarietal red wines made with Grenache (17 samples), Tempranillo (11 samples), Cabernet Sauvignon (12 samples) and Merlot (12 samples) grapes have been analysed by HRGC–MS to obtain quantitative data on 47 odorants previously identified as potential aroma contributors by olfactometric techniques. Thirty-three odorants were present in the wines at concentrations higher than their corresponding odour thresholds. These include ethyl octanoate, β-damascenone, ethyl hexanoate, isovaleric acid and isoamyl acetate as the most important, which together with isoamyl and β-phenylethyl alcohols, fatty acids, 2,3-butanedione and ethyl butyrate are always found at concentrations higher than their odour thresholds. In some cases the ethyl esters of isobutyric and isovaleric acids, β-ionone, methionol, isobutyric acid, ethyl cinnamate, ethyl dihydrocinnamate, γ-nonalactone, eugenol, c-3-hexanol, geraniol, guaiacol, 3-isobutyl-2-methoxypyrazine, 4-ethylguaiacol, acetoin and t-whiskylactone were at a concentration high enough to be odour-active. There were 30 compounds that were found to differ significantly between varieties. These include 3-isobutyl-2-methoxypyrazine, isoamyl acetate, isovaleric acid, ethyl isobutyrate, ethyl isovalerate, fusel alcohols, c-3-hexenol, methionol, eugenol, guaiacol and γ-nonalactone.

© 2000 Society of Chemical Industry

Quantitative determination of the odorants of young red wines from different grape varieties

THE molecular feature common to the many different sweet tasting compounds has been sought for many years1. For the sugars, it was proposed2–5 that the sweet unit is the glycol group, and that intensity of sweetness varied inversely with the degree to which glycol OH groups appear to be intramolecularly hydrogen bonded. It is now apparent that vicinal OH groups in the glycol unit need to be approximately gauche, or in a staggered conformation. Vicinal OH groups which are in the anti conformation apparently are too far apart to cause sweet taste. Glycol OH groups which are eclipsed probably participate in an intramolecular hydrogen bond which competitively inhibits interaction of glycol with the receptor site. These steric features of sweet and non-sweet sugar glycol units are shown in perspective in Fig. 1. Glycol conformational parameters, and the gross conformation of pyranose and furanose rings, have been used to explain the varying sweetness of the sugars2–5.

Molecular Theory of Sweet Taste

A Procedure for the Sensory Analysis of Gas Chromatographic Effluents

A device that simulated retronasal aroma was constructed from a 1 L blender incorporating purge-and-trap, synthetic saliva addition, temperature regulation to 37 °C, and blending at shear rates reported to occur during eating. Volatiles were collected on a silica trap, solvent desorbed, and quantitated by GC/FID or GC/MS with high precision (CV < 5%) and sensitivity (micrograms per liter). Increasing the temperature from 23 to 37 °C and adding shear increased volatility. The addition of synthetic saliva to a model grape beverage (pH 2.6) increased the pH and the volatility of the bases, 2-acetylpyridine, methyl anthranilate, o-aminoacetophenone, and 2-methoxy-3-methylpyrazine, relative to a model neutral compound, 1,8-cineole. The data were consistent with a sensory test that showed a significant shift in the perception of minty to nutty upon the addition of synthetic saliva to a mixture of 1,8-cineole and 2-acetylpyridine in an acid medium. The volatility of eight flavor compounds was investigated in a soybean oil versus water matrix. The volatilities of α-pinene (log P = 3.75), ethyl 2-methylbutyrate, 1,8-cineole, 2-methoxy-3-methylpyrazine, and methyl anthranilate decreased by factors of 8000, 130, 100, 7, and 3 upon oil addition ; however, butyric acid did not decrease, and polar maltol (log P = 0.02) actually increased.

Simulation of Retronasal Aroma Using a Modified Headspace Technique: Investigating the Effects of Saliva, Temperature, Shearing, and Oil on Flavor Release

GC/O analysis of canned lychees indicated that cis-rose oxide, linalool, ethyl isohexanoate, geraniol, furaneol, vanillin, (E)-2-nonenal, β-damascenone, isovaleric acid, and (E)-furan linalool oxid...

Terry E. Acree

Papers

Molecular Theory of Sweet Taste

A Procedure for the Sensory Analysis of Gas Chromatographic Effluents

Simulation of Retronasal Aroma Using a Modified Headspace Technique: Investigating the Effects of Saliva, Temperature, Shearing, and Oil on Flavor Release

Similarities in the aroma chemistry of Gewürztraminer variety wines and lychee (Litchi chinesis sonn.) fruit.

Charm analysis of apple volatiles