Odour-active compound

Twenty-nine odour-active compounds were detected by using aroma extract dilution analysis (AEDA) [60]. The results of AEDA together with GC-MS analysis showed ethyl 2-methylbutanoate (described as fruity flavour), followed by methyl 2-methylbutanoate and 3-methylbutanoate (fruity, apple-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (sweet, pineapple-like, caramel-like), d-decalactone (sweet, coconut-like), l-( ,Z)-3,5-undecatriene (fresh, pineapple-like), and a unknown compound (fruity, pineapple-like) as the most odour-active compounds. 

Table 11.1 Odour-active compounds involved in varietal aroma of wine ...

Schieberle, P. 1996. Odour-active compounds in moderately roasted sesame. Food Chem. 55 145-152. 

Moyano, L., Zea, L., Villafuerte, L., and Medina, M. (2009). Comparison of odour active compounds in sherry wines processed from ecologically and conventionally Brown Pedro Ximenez grapes. ]. Agric. Food Chem. 57, 968-973. 

Table 13.3. Odour-active compounds detected in an aroma extract of fenugreek seeds.

Burghalter, G., Steffen, C., Puhan, Z. Cheese, processed cheese, and whey. In Ullmann s Enzyclope-dia of Industrial Chemistry. 5 Edition, Volume A6 (Eds. F.T. Campbell, R. Pfefferkorn, J.F. Rounsav-ille) Verlag Chemie, Heidelberg, 1986, pp. 163 Creamer, L.K., Richardson, X, Parry, D.A.D. Secondary structure of bovine ttsi- and 3-casein in solution. Arch. Biochem. Biophys. 211, 689 (1981) Czerny, M., Schieberle, R Influence of the polyethylene packaging on the adsorption of odour-active compounds from UHT-milk. Eur. Food Res. Tech-nol. 2007, in press... 

Besides nutrients, foods contain many substances that influence the food sensory impression and its organoleptic properties. These food constituents are known as sensoriaUy active compounds. They determine the sensory value (quality) of foods, inducing an olfactory sensation (perception), which is described as the aroma, odour and smell, gustative perception, which is the taste, visual perception, which is the colour, haptic (tactile) perception, which is the touch and feel, and auditorial perception, which is the sound. The olfactory sensation is derived from odour-active compounds and the gustative perception from taste-active compounds. Flavour is the sensory impression determined by the chemical senses of both taste and smell and is caused by flavour-active food components. Haptic sensation is the texture, which is affected mainly by high molecular weight compounds, such as proteins and polysaccharides, often referred to collectively as hydrocoUoids. Geometric aspects of texture that evoke both haptic and visual sensations symbolise the terms appearance and shape. 

For completeness, this chapter also includes some non-volatile substances that do not have the potency of odour-active compounds. However, these substances may frequently be precursors of volatile compounds or have other important properties. 

Almost aU saturated aliphatic aldehydes, starting with formaldehyde (methanal) and ending with dodecanal, are important odour-active compounds. Particularly important odour-active compounds are monoterpenic aldehydes. 

During heating and long storage of foods, esters may also be formed in small quantities as secondary odour-active compounds. For example, esters are formed during aging of wines and spirits by esterihcation of carboxylic acids with alcohols (ethanol or fusel oil alcohols, but the non-enzymatic esterification is a very slow reaction), acidolysis (reaction of acids with esters), alcoholysis (reaction of alcohols with esters) or ester exchange (reaction of esters with other esters). 

Lactones occur as natural odorants in aU major food commodities, including meat and meat products, milk, dairy products, cereals, fruits, vegetables and various beverages, such as tea, wine and spirits. Odour-active compounds in foods are y-and 5-lactones derived from aliphatic saturated and unsaturated y-hydroxycarboxyHc and 5-hydroxycarboxylic acids derived from fatty acids or sugars, but some lactones also arise from other precursors (e.g. mint lactone is a terpenoid compound and pantolactone is produced by hydrolysis of pantothenic acid via pantoic acid). Some lactones derived from aromatic hydroxycarboxyhc acids are also common compounds. The most important representatives of these compounds are phthahdes that are 3fL-isobenzofuran-l-ones (8-98) and coumarins (8-99) that are 2fL-l-benzopyran-2-ones (5-lactones of 2-hydroxycinnamic acids). 

Dimethylsubstituted unsaturated y-lactones that result from the autoxidation or photooxidation products of furan fatty acids are called bovolides. Bovolides have been found in some plants, butter, cooked meats and seafood. The especially important odour-active compounds are 3,4-dimethyl-5-pentyhdene-511-furan-2-one, called bovolide (Figure 8.55), and 3,4-dimethyl-5-pentyl-5H-furan-2-one that is known trivially as dihydrobovoHde. Both compounds are characterised by their smeU, which resembles celery. The mechanism of autoxidation of fatty acids is described in detail in Section 3.8.1.8.2. 

The key components of fresh grapefruit juices with a typical grapefruit odour are both isomers of p-mentha-l-en-8-thiol (8-188). The (- -)-(Ji)-enantiomer is present in minute concentrations (less than 1 (xg/kg), but has a very low odour threshold concentration. The (-)-(S)-p-mentha-l-ene-8-thiolhas aweak and non-specific smell. Of the other sulfur compounds, 4-mercapto-4-methylpentan-2-one (8-125) is significant, and also occurs in blackcurrants, some hop cultivars, aromatic wines and basil. A relatively high content of sesquiterpenoids is also typical. The smell and bitter taste of grapefruits arise from (-l-)-nootkatone and (-1-)-8,9-didehydronootkatone. Important odour-active compounds are numerous cyclic ethers, which are likewise found in other essential oils. For example, the essential oil contains about 13% of hnalool oxides that arise from linalool via 5,6-epoxide, and another important epoxide is ( )-4,5-epoxydec-2-enal. The fresh odour of juices is mainly influenced by aliphatic aldehydes, such as acetaldehyde. 

The typical components of the aroma of celery (Apium grave-olens var. rapaceum, Apiaceae) and celeriac (A. g. var. duke) are numerous dihydrophthalides, tetrahydrophthalides, hexahydroph-thalides and phthalides. The main odour-active compound is... 

Refers to the use of human assessors as a sensitive and selective detector for odour-active compounds. The aim of this technique is to determine the odour activity of volatile compounds in a sample extract, and assign a relative importance to each compound. 

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