Just noticeable differences in component concentrations modify the odor quality of a blending mixture.

The odors we perceive are mainly the result of mixtures of odorants that, however, are commonly perceived as single undivided entities; nevertheless, the processes involved remain poorly explored. It has been recently reported that perceptual blending based on configural olfactory processing can cause odorant mixtures to give rise to an emergent odor not present in the components. The present study examined whether specific component proportions are required to elicit an emergent odor. Starting from the composition of a ternary target mixture in which an emergent pineapple odor was perceived, 4 concentration levels of each component were chosen to elicit just noticeable differences (JNDs). Each combination of levels was used to design sample mixtures. Fifteen subjects evaluated the intensity, typicality, and pleasantness of each sample mixture against the target mixture in a paired-comparison protocol. Statistical modeling showed that a variation of less than 1 JND in one of the components was sufficient to induce a significant decrease in pineapple odor typicality in the ternary mixture. This finding confirms previous findings on perceptual blending in simple odorant mixtures and underscores the human ability to discriminate between odor percepts induced by mixtures including very similar odorant proportions.

Potent aroma compounds of two red wine vinegars.

Gas chromatography olfactometry (GCO) was used to determine key aroma compounds of two red wine vinegars. Sensory analysis was performed to choose the best neutralization agent of acetic acid (NaOH or MgO) and to test representativeness of four extracts obtained by different methods (dichloromethane extraction, XAD-2, mixture of XAD-2 and XAD-7, and Extrelut resins extraction). Neutralization with NaOH followed by dichloromethane extraction was selected to extract volatile compounds of vinegars. Key odorant compounds were determined by GCO based on detection frequency with 13 people. In the two red wine vinegars, 13 odors were perceived by at least 70% of the panelists, and 8 compounds among the 13 were identified: acetic acid, 3-methylbutyric acid, 2-phenyl-1-ethanol, 2, 3-butanedione, butyric acid, 2-methylbutyric acid, mixture of 2- and 3-methyl-1-butanol, and two newly identified compounds in vinegar, 3-hydroxy-2-pentanone and 3-(methylthio)-1-propanal. Quantification of all the volatile compounds was performed by GC-FID, and 10 other compounds were identified for the first time in wine vinegar.

Effect of antioxidants on the flavor characteristics and the gas chromatography/olfactometry profiles of champagne extracts.

This paper aims to investigate the possibility of oxidation of the flavor active constituents of champagne wines during the critical steps of the extraction for analytical purposes and to estimate its consequences on the extract's aroma characteristics. The investigation uses conventional sensory and GC/O analyses. Triangle and similarity sensory tests carried out on champagne samples and on their extracts show that the absence of antioxidants implies a deterioration of the aroma quality. Conversely, the use of 2-tert-butyl-4-methoxyphenol (BHA) as antioxidant gives an extract with an odor judged to be more similar to the original odor of the champagne. The alteration in the odor of the unprotected extracts is explained, from GC/O and GC/MS analyses, as three types of uncontrolled reactions. These are, first, the chemical oxidation of the fusel alcohols and the amino acids; second, the oxidation of sensitive flavor compounds such as enolic lactones and monoterpenic alcohols; and, third, the hydrolysis of fatty acid esters and saturated gamma-lactones. A systematic use of BHA during flavor extraction is therefore advisable, in particular when oxidation phenomena such as wine aging are under study.

Odor intensity evaluation in gas chromatography-olfactometry by finger span method.

This paper describes the potential of evaluating odor intensities in a gas chromatographic effluent by cross-modality matching with the finger span (GC-O-FSCM). A simple prototype is described that allows the precise measurement and acquisition of the distance between the thumb and another finger during the analysis. The stimulation of panelists at the sniffing port with ethyl butyrate shows a log-log relation between peak height values obtained from finger span and stimulus concentrations. It also shows that all panelists are able to perform this task but with different precision, which is used to select them. A triplicate evaluation by GC-O-FSCM of the intensity of flavor constituents in synthetic solutions shows that a four-member panel is perfectly able to determine most of the characteristics of the solutions and to create a finger span multidimensional space highly correlated with the theoretical intensity space.

Measurement of interactions between polysaccharides and flavour compounds by exclusion size chromatography: advantages and limits.

Interactions between flavour compounds and polysaccharides have been studied by exclusion size chromatography, the Hummel and Dreyer method. Hydrogen bonding was found between 2-acetyl thiazole and dextrines of different degrees of polymerisation. The number of binding sites and the affinity constant increase by increasing the degree of polymerisation. Hydrogen bonding was also responsible for the interactions between xanthane and 1-octen-3-ol or 2-acetyl pyrazine, with 1 mole of 1-octen-3-ol bound per pentasaccharide repeating unit. Unfortunately, the number of flavour compounds, which can be studied with this method, is limited due to their low water solubility and their low UV absorption.

Artifacts and contaminants in the analysis of food flavor.

The qualitative and quantitative complexity of food flavor makes its complete analysis rather difficult, involving a series of necessary successive steps, from the transport of the samples to the laboratory to the final quantification of the volatiles in the extract. However, because of the minute amounts of most odorous substances in food, these numerous manipulations of the sample are often the cause of alterations of the flavor, and complementary techniques are generally recommended to get a clear idea of its original composition. Arguments and clues, from 95 publications dealing with the analysis of various types of food, demonstrating that some of the volatile substances finally identified could have been in fact contaminants or artifacts arising from the analysis itself are presented. For practical reasons, the logical sequence of treatments successively applied to the sample throughout the flavor analysis is adopted.

Chemicals involved in honeybee-sunflower relationship.

We present a review of work on the plant chemicals involved in the honeybee-sunflower model system. Combined behavioral and chemical analyses were conducted under natural and controlled conditions. First the distribution of forager bees' visits on two pairs of sunflower genotypes producing a different level of hybrid seed yield was recorded under pollen-proof tunnels. Mirasol parental lines producing high seed yields were visited at random, whereas forager bees visited preferentially the female parental line of Marianne, resulting in low seed yield. Nectar samples collected on the genotypes were analyzed by gas chromatography. Fructose, glucose, and sucrose were identified. Parental lines of Mirasol showed similar sugar profiles, whereas the female line of Marianne contained higher amounts of sucrose than the male line. We assume that the bees' preferences between genotypes might rely on differences in the sugar composition of floral nectars, especially in the amount of sucrose. Aromas from headspace collection were compared between pairs and periodically during the flowering period. Of the 144 components indexed for Marianne lines and 136 components for Mirasol lines, 17 of the components for Marianne lines and 18 for Mirasol lines differed significantly according to flowering stage. Significant differences appeared in eight of the 134 components of Marianne lines and in 20 of the 250 components for Mirasol lines. Such differences, even restricted to a few components, might account for honeybees' discrimination between genotypes or flowering stage. Experiments then were conducted in a flight room using an artificial flower device. A total volatile extract was used as a conditioning scent previous to the test where the total extract was successively compared to several of its subfractions. Fractions significantly less visited than the total extract were discarded, whereas fractions confused with the total extract were kept. From step to step, a restricted fraction of 28 polar components, among which 15 were identified, was shown to be as active as the initial conditioning extract. These data emphasized honeybees' abilities to generalize from simplified to more complex chemical information. Finally, this work considers the possible use of such plant chemicals, from nectars or aromas, either as targets for genetic modification of crop plants or as direct attractants when sprayed on the crop, for the improvement of entomophilous cross pollination.

Sunflower aroma detection by the honeybee : Study by coupling gas chromatography and electroantennography.

Combined electrophysiological recordings (EAG) and gas chromatographic separation were performed in order to investigate which volatile chemical components of a sunflower extract could be detected by honeybee workers and thus are likely to trigger the foraging behavior. A direct coupling device allowed for the stimulation of the antennal receptors with individual constituents of a polar fraction of the flower aroma shown to be attractive to bees. More than 100 compounds were separated from the extract. Twenty-four compounds elicited clear EAG responses. These compounds were identified by mass spectrometry (electronic impact and chemical ionisation). Both short- and long-chain aliphatic alcohols, one short-chain aliphatic aldehyde, one acid, two esters, and terpenic compounds were found to stimulate the antennal receptors. Six compounds identified in previous behavioral experiments were found to exhibit EAG activity. The chemicals screened by this method may be used for recognition of the plant odor and the selective behavior of honeybees.

Sunflower volatiles involved in honeybee discrimination among genotypes and flowering stages.

In order to define the part of olfactory cues in the selective behavior of honeybees, observation on their foraging behavior was carried out on various sunflower genotypes in parallel with chemical analysis of aromatic extracts of the genotypes. Foragers show a preference for the early stages of flowering and, when they are given a choice between couples of parental lines of two commercial hybrids, Marianne and Mirasol, they are randomly distributed on Mirasol parents, but they prefer the female line of Marianne. The comparison of relative proportions of compounds among aromagrams obtained from head space trapping from the two couples of genotypes, reveals (1) a phenological stage effect for 17 compounds among 144 indexed compounds for Marianne lines and for 18 among 136 indexed compounds of Mirasol lines; most of these compounds exhibit higher relative proportions in the early flowering stages, which is related to plant attractiveness towards honeybees; (2) a sex effect for 33 compounds among 144 for Marianne lines and for 14 compounds among 136 for Mirasol lines; further semiquantitative analyses reveal a sex effect for only eight compounds of 134 for Marianne lines and 20 compounds of 250 for Mirasol lines, which represents less than 10% of the indexed compounds. These discriminatory compounds were partly identified by coupled GC-MS. Possible relations between such phenological and genotypical volatile fluctuations and forager attraction are discussed.

Molecular parameters involved in bee-plant relationships: a biological and chemical approach.

Honeybee-plant relationships are based on a conditioning process in which olfactory (plant aroma) and gustatory cues (mainly nectars) are closely linked, leading to a selective foraging behaviour. Among crops dependent upon entomophilous cross-pollination, the sunflower has recently undergone extensive expansion due to hybrid variety selection. Sunflower hybrid seed production is strictly dependent upon pollinating insects, mainly the honeybees, but foragers may have preferences among the parental lines, leading to a lack of pollen carriage and consequently to a decrease of hybrid seed yield. In order to define the role of plant chemicals (aromas, nectars) involved in the pollination process, we set up a study combining behavioural and chemical assays. It appears that even though volatile chemical blends are much more complex compared to glucidic blends, for both kinds of cues only a 'limited chemical pattern' is responsible for foragers' choices. Therefore, it is henceforth possible to take these molecular criteria into account for plant improvement.

Selective olfactory choices of the honeybee among sunflower aromas: A study by combined olfactory conditioning and chemical analysis.

A bioassay based on an olfactory conditioning method simulating the foraging situation in laboratory conditions was coupled with chemical analysis of volatile sunflower blends. Behavioural data obtained from for-agers'responses to volatile fraction point out that honeybees need to use only a limited fraction acting as a "simplified aromatic pattern" of the plant, among hundreds of compounds constituting the whole aroma. This active fraction included 27 polar compounds among which 14 were identified. Extension of such data to crop pollination and plant improvement is discussed.