Odor contributions

Common electronic noses are so called as they are often aimed at detection of odorous compounds it is generally not clear that discriminations are based on odorous rather than non-odorous, and possibly incidental, components of the headspace. In the headspace of a food sample, odorants contributing to the flavour may be present in low concentrations, whereas non-odorous molecules can be present in much larger numbers and higher concentration. In such cases. 

The highest OAVs were found for 4-hydroxy-2,5-dimethyl-3(2H)-fura-none, followed by ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, methyl 2-methylbutanoate and ( ,Z)-l,3,5-undecatriene. It is assumed that these odorants contribute strongly to the aroma of pineapples [50]. However, FD factors and OAVs are functions of the odorants concentrations in the extract, and are not psychophysical measures for perceived odour intensity [71,72]. To take this criticism into account, aroma models are prepared on the basis of the results of the quantitative analysis (reviewed in [9]) and in addition omission experiments are performed [9]. 

Vanillin, syringaldehyde, and related phenolic products derived from lignin appear to be important in the desirable odor contributed to beverages by oak barrels (25, 26, 27). These substances are present in the wood, but more appears in the beverage than simple extraction seems to allow. Also the odor of vanillin seems to increase with time and mellowing of the beverage compared with a fresh extract of new wood (25). 

Most natural organic materials which have strong odors, either agreeable or disagreeable, contain either mercaptans or alkyl sulfide. Various mercaptans have been found in crude oil, and the odor contributed by small quantities of these materials led to the name sour crude. 

In the following chapter, methods enabling the selection of those odorants contributing mainly to food flavors will be discussed with special emphasis on sensory experiments aimed to verify the flavor potency of the proposed key odorants. Furthermore, strategies to characterize flavor precursors in the raw materials will be described. 

Crust volatiles were isolated immediately after baking by extraction with dichloromethane and sublimation in vacuo ( ). Application of aroma extract dilution analysis 6) to the acid-free crust extract led to the detection of 31 odorants. After separation and enrichment, these compounds were identified by comparison of the MS/EI, MS/Cl and retention data on two columns of different polarity to reference compounds. Aroma quality was also assessed. The results of the identification experiments (Table I) revealed that 2(E)-none-nal (No. 1), followed by 2(E),4(E)-decadienal (No. 2) and 3-methyl-butanal (No. 3) showed the highest FD-factors in the crust of the chemically leavened bread. Additionally l-octen-3-one, 2(Z)-nonenal, 2(E),4(E)-nonadienal and an unknown compound with a metallic odor contributed high FD-factors to the overall flavor (For a discussion of FD-factors, see Chapter by Schieberle and Grosch, this book). 

Citrus oil dominates this class of essential oil. It is obtained by the cold press method with the exception of lime oil, which is also prepared by steam distillation of essential oil separated during the production of juice.106,107 Aside from bergamot, these oils are primarily monoterpene hydrocarbon mixtures of which (if)-limonene (3) is usually the dominant compound. Since odor contribution of this monoterpene compound is low, it is often removed by distillation or repeated solvent extraction. The resulting oil rich in odor-active compounds is called terpeneless oil and is used extensively. In the case of bergamot and lemon oils, psoralen derivates like bergaptene (64) causing photosensitivity are problematic, and those for fragrance use are rectified to remove it (Table 8). 

Relative odor contribution of components Considered individually, none of the compounds identified duplicated the flavor of the Black Truffle. However, according to the judges, dimethyl sulfide was determined to have a great Importance to the final aroma Impression. In the same way, 2-butanone ind anisole were found to be responsible for an off-flavor characteristic of over-mature truffles. 

Though pineapple flavor has been extensively studied relatively little work has been done on the odor properties and significance of the various constituents ( , ) This study investigates the odor contribution of various constituents. The volatiles from three parts of fresh pineapple, the crown, pulp and intact fmit were examined. 

To approach the situation in food, OAVs are calculated on the basis of odour threshold values which have been estimated in a medium that predominates in the food, e.g. water, oil, starch. As an example the OAVs of the key odorants of baguette crust are listed in Table 6.26. The highest OAVs were found for the roasty smelling 2-acetyl-1-pyrroline (no. 7), followed by furaneol (no. 20), 2,3-butanedione (no. 2), (E)-2-nonenal (no. 13), l-octen-3-one (no. 9) and methional (no. 6). It is assumed that these odorants contribute strongly to the aroma of baguette crust. 

Kerler, J., Grosch, W. (1996) Odorants contributing to warmed-over flavor (WOF) of refrigerated cooked beef. J. Food Sci. 6, 1271-1284... 

Darriet, P, Pons, M., Henry, R., Dumont, O., Findeling, V., Cartolaro, P., Calonnec, A., and Dubourdieu, D. (2002). Impact odorants contributing to the fungus type aroma from grape berries contaminated by powdery mildew... 

Indole (46) and 2 phenylethanol (47) are both shikimate derivatives. Indole is particularly associated with jasmine. It usually occurs in jasmine absolute at a level of about 3%-5% and makes a very sign cant odor contribution to it. However, it does occur in many other essential oils as well. 2-Phenylethanol occurs widely in plants and is especially important for rose where it usually accounts for one third to three quarters of the oil. The structures of both are shown in Figure 6.10. 

Grosch, W, et al.. Studies on the formation of odorants contributing to meat flavors, in Progress Flavour Precursor Studies, P. Schreier, P. Winterhalter, Eds., Allured Publ., Carol Stream, 1993, p. 329. 

Dihydro-1,1,6-trimethyl naphthalene (Table 3.59) can be formed by a degradation of neoxanthin and other carotinoids during the storage of wine. It smells like kerosene (threshold 20pg/kg, wine). It is thought that this odorant contributes considerably to the typical aroma of white wine that was stored for a long period in the bottle. The compound may cause an off-flavor in pasteurized passion fruit juice. 

Wines infected with either lactic acid bacteria (particularly heterofermentative strains) or Dekkera/Brettanomyces yeast can potentially produce mousy off-flavor for which 2-ethyltetra-hydropyridine, 2-acetyltetrahydopyridine and 2-acetylpyrroline are responsible. The impact odorants contributing to mushroom off-flavour in wines are oct-l-en-3-one and non-l-en-3-one. 

Pons M., Dauphin B., La Guerche S., Pons A., Lavigne-Cruege V., Shinkaruk S., Banner D., Richard T., Monti J.-P., Darriet P. Identification of impact odorants contributing to fresh mushroom off-flavor in wines incidence of their reactivity with nitrogen compounds on the decrease of the olfactory defect. Journal of Agricultural and Food Chemistry, 59 3264-3272 (2011). 

Sensory experiments have shown that the odor of this compound was similar after appropriate dilution, but not identical, when evaluated in comparison to the sunstruck flavor in beer by a trained sensory panel [5]. It was, therefore, assumed that, besides MBT, further odorants contributed to the flavor difference observed in beer during exposure to light [6]. However, this assumption has not yet been confirmed by sensory studies and/or quantitative data. Since its detection by means of headspace gas chromatography was not successful [5], numerous methods have been proposed for MBT enrichment and quantation [7-10], and concentrations... 

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