Odour definition

Sulphur. Moisten the centre of a filter-paper with lead acetate solution. Then add about 10 ml. of dilute hydrochloric acid to the residue in the evaporating-basin, and at once cover the latter with the paper. If zinc sulphide is present in the residue, the hydrogen sulphide evolved will give a definite daA brown coloration with the lead acetate paper. The presence of hydrogen sulphide can often be confirmed by its odour. 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

In the following some aspects of the guidelines are given in detail. Guideline VDI 3881 consists of four parts. The drafts of parts 1, 2, and 3 were published in the VDI handbook. Part 4 is in preparation. The draft of part 1 was already revised. The new version will be published in a few months. The most important result of the revision is the definition of odour concentration expressed as odour units per cubic meter (GE/m 3). According to this definition one odour unit is the amount of odorants in one cubic meter of air at odour threshold level. The new definition is a real concentration and gives a better form of input parameter for dispersion models. 

Although the results are not yet analysed it can be concluded that the threshold values agree. Results of this study will also be incorporated in the definitive version of the chapter on odours in the Air Pollution Control Manual. The draft is currently with the printer and will be released soon (4). In coming years a ringtest will probably be organised under supervision of the Netherlands Standards institute. Eveiy research institute, provincial authority and industiy will be invited to participate in this ringtest. 

On the other hand, the set of data turned out to be a useful tool for calculating the limitations of each odour reducing method under definite conditions. The results also allowed precautions for appropriate process management under conditions causing high levels of odorous compounds. 

The odour threshold may be lower than the limit of analytical detection (e.g. sulphur compounds, pyrazines). In such cases authenticity assessment is definitely impossible. 

The affinity of selenium for oxygen is less than that of sulphur. The dioxide, SeQ2, is well defined. The trioxide, Se03, is much less stable than its sulphur analogue, and until recently all attempts to isolate it have been unsuccessful (see p. 331). Selenium sesquioxide, Se203, has not been definitely isolated.1 An oxide of composition Se304 has been described,2 but its existence needs confirmation. The existence of a lower oxide, SeO, postulated to explain the characteristic odour of selenium when vaporised in air, is improbable.3... 

Essential oil Many definitions exist, referring to the odoriferous and volatile products from natural sources. Usually extracted by expression or steam distillation from a single species, producing an essential oil that corresponds to that species in chemical composition and odour. 

The difference between the odours of two optical isomers of carvone has been characterised by various authors. Russell and Hills have described that 4S-carvone has the odour of caraway and 4R-carvone has the odour of spearmint. They have stated that these observations lend a definite support to stereochemical considerations of odour pereeption... 

Characteristics yellow-brown liquid, sweet mint-like odour with a definite blackcurrant note, bitter taste. 

The International Organisation of the Flavour Industry (lOFI) defines flavour enhancer as a substance with little or no odour at the level used, the primary purpose of which is to increase the flavour effect of certain food components well beyond any flavour contributed directly by the substance itself [5]. The EU definition of flavour enhancers is substances that enhance the taste and/or odour of a food [6]. 

The flavour of a food consists of odour, taste, and haptic and tactile sensations in the mouth ( mouthfeel ) (Fig. 3.52). This means that a flavour modifier may affect odour, taste, and/or mouthfeel of a food. Usually, only taste and/or odour are affected, although maltol and ethyl maltol have been reported to be effective in improving the mouthfeel in low-fat food systems [7]. Because of lack of a clear definition, I shall classify flavour modifiers into the five categories shown in Table 3.46. Based on this... 

At this point, it is important to clarify a few terms that are often used in the context of this chapter. Flavour is usually divided into the subsets taste and smell, which are perceived in the mouth and the nose, respectively [3], The terms aroma and odour are not well defined and often used as synonyms. Qdour is best reserved for the smell of food before it is put into the mouth (nasal perception) and aroma for the retronasal smell of food in the mouth. In this paper, we mainly use the terms aroma and taste , as well as flavour comprising sensory notes imparted by both volatile and nonvolatile compounds (odorants and tastants). In the public domain, however, taste is often used as a synonym for flavour . Proper definitions of these terms are ... 

Lubricant base oils must meet minimum performance characteristics of viscosity, viscosity index, pour point and volatility, all of which must meet required standards. When dealing with re-refined base oils, additional characteristics such as colour and odour must also be considered. These properties, of dark colour and odour, are readily perceived by customers and consumers as representing deficiencies in quality. Many examples of re-refined base oils have a definite, characteristic, oxidised or cracked odour which may be totally unacceptable in some countries and markets. Table 15.2 gives quality guidelines for the acceptance of re-refined 150 and 500 base oils. 

Diterpenes have, by definition, 20 carbon atoms in their structure. This means that very few are sufficiently volatile to possess an odour. One diterpene is used in perfumery because it and the derivatives concerned are odourless. That is, they are used as solvents. In view of their hydrophobicity and low volatility, these solvents also have fixative properties. Abietic acid is a major component of tall oil, the residue from distillation of turpentine. Esterification and hydrogenation produces two solvents, as shown in Scheme 4.36. 

The Codex Alimentarius standard includes limits for acidity, volatile matter, insoluble impurities, peroxide value, colour, odour, taste, iron, copper, K27o, AK, permitted additives, contaminants (lead, arsenic, halogenated solvents), refractive index, saponification value, iodine value and unsaponifiable matter. Physical and chemical constants, such as iodine value and saponification value, are not found in the EU regulation. This is explained by the fact that more definite information is obtained by determining fatty acid composition, sterol and wax composition, trans fatty acid content, stigmastadiene, and so on. 

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