Threshold values ketones

Some reported odor threshold values for nootkatone were considerably lower than the taste threshold values. Odor thresholds of 0.8 ppm in water and 30 ppm in air were reported for (+)-nootkatone, the enantiomer of this sesquiterpene ketone present in grapefruit (35). An odor threshold of 0.15 ppm in water was reported for crystalline nootkatone isolated from grapefruit oil (36). In that study, mother liquor from crystallization of nootkatone was 30 times more potent (odor threshold of mother liquor 5 ppb) than nootkatone alone and the panel felt that the aroma of the mother liquor more closely resembled grapefruit aroma... 

Methylcyclopentenolone has a strong caramel-like, maple-like or licorice-like aroma (31j, and was found in browned, dehydrated orange juice at the 1 ppm level (43). Its synergistic flavor effect with other compounds, such as 5-methyl-2-furfural and N-ethylpyrrole- 2-carboxyaldehyde, was reported (43). Although it is present at levels five times below its threshold value, it still impacts on the heat-abused flavor of dehydrated orange juice. This ketone probably results from amine-assisted sugar degradation (45). 

A variety of compounds such as hydrocarbons, alcohols, furans, aldehydes, ketones, and acid compounds are formed as secondary oxidation products and are responsible for the undesirable flavors and odors associated with rancid fat." The off-flavor properties of these compounds depend on the structure, concentrations, threshold values, and food systems. Aliphatic aldehydes are the most important volatile breakdown products because they are major contributors to unpleasant odors and flavors in food products. 

A variety of compounds such as hydrocarbons, alcohols, furans, aldehydes, ketones, and acid compounds are formed as secondary oxidation products and are responsible for the undesirable flavors and odors associated with rancid fat. The off-flavor properties of these compounds depend on the structure, concentration, threshold values, and the tested system. Aliphatic aldehydes are the most important volatile breakdown products because they are major contributors to unpleasant odors and flavors in food products. The peroxidation pathway from linoleic acid to various volatiles is determined in several researchs, - by using various techniques (Gas chromatography mass spectrometry, GC-MS, and electron spin resonance spectroscopy, ESR), identified the volatile aldehydes that are produced during the oxidation of sunflower oil. In both cases, hexanal was the major aldehyde product of hydroperoxide decomposition, whereas pentanal, 2-heptenal, 2-octenal, 2-nonenal, 2,4-nonadienal, and 2,4-decadienal were also identified. 

Ketones form a minor fraction in alcoholic beverages. Ketones can be said to be potential aroma compounds. In particular, diketones such as 2,3-butanodione and 2,3-pentanodione are of great importance to the aroma of alcoholic beverages because of their low sensory threshold values. Those aldehydes with 8-10 carbon atoms, such as (E)-2-nonenal, octanal, nonanal, decanal, or (E,Z)-nonadienal, are also strong odorants, related with important off-flavors. 

The hydroperoxy epidioxides formed from photosensitized oxidized methyl linoleate are important precursors of volatile compounds, which are similar to those formed from the corresponding monohydroperoxides. Thus, 13-hydroperoxy-10,12-epidioxy-tra 5 -8-enoic acid produces hexanal and methyl lO-oxo-8-decenoate as major volatiles (Figure 4.24). The 9-hydroperoxy-10,12-epidioxy-rrans-13-enoic acid produces 2-heptenal and methyl 9-oxononanoate. Other minor volatile products include two volatiles common to those formed from the monohydroperoxides, pentane and methyl octanoate, and two that are unique, 2-heptanone and 3-octene-2-one. The hydroperoxy epidioxides formed from autoxidized methyl linolenate produce the volatiles expected from the cleavage reactions of linolenate hydroperoxides, and significant amounts of the unique compound 3,5-octadiene-2-one. This vinyl ketone has a low threshold value or minimum detectable level, and may contribute to the flavor impact of fats containing oxidized linolenate (Chapter 5). 

The odor threshold values for methyl ketones are substantially higher than those for aldehydes (cf. Tables 3.32 and 3.47). Nevertheless, they act as aroma constituents, particularly in flavors of mold-ripened cheese (cf. 10.2.8.3). However, methyl ketones in coconut or palm oil or in milk fat provide an undesirable, unpleasant odor denoted as perfume rancidity . 

Of all Ci3-norisoprenoids, P-damascenone and P-ionone, smelling like honey and violets respectively, have the lowest odor threshold values (Table 3.59). Precursor of P-damascenone is neoxanthine, out of which the Grasshopper ketone (I in Formula 3.142) is formed by oxi-... 

The 2003 ACGIH threshold limit value-time-weighted average (TLV-TWA) for dipropyl ketone is 50 ppm (233mg/m ). 

Hansen LF, Nielsen GD Sensory irritation and pulmonary irritation of -methyl ketones Receptor activation mechanisms and relationships with threshold limit values. Arch Toxicol 68 193-202, 1994... 

The 2003 ACGIH ceiling-threshold limit value (C-TLV) for methyl ethyl ketone peroxide is 0.2 ppm (1.5mg/m ). 

Environmental criteria have been established for many of these, but the utility and applicability of such criteria for indoor environments is controversial for at least four reasons. Eor example, the goals of the threshold limit values often do not include preventing irritation, a primary concern in indoor environments with requirements for close eye work at video display terminals. For most of the pollutant categories, the problem of interactions, commonly termed the multiple contaminants problem , remains inadequately defined. Even for agents that are thought to affect the same receptor, such as aldehydes, alcohols, and ketones, no prediction models are well established. Finally, the definition of representative compounds for measurement is unclear. That is, pollutants must be measurable, but complex mixtures vary in their composition. It is unclear whether the chronic residual odor annoyance from environmental tobacco smoke correlates better with nicotine, particulates, carbon monoxide, or other pollutants. The measure total volatile organic compounds is meanwhile... 

Trace Components The trace components of landfill gas mainly comprise a range of alkanes and alkenes, and their oxidation products (aldehydes, ketones, alcohols and esters). Waste Management Paper 26 (DoE, 1986) lists 108 compounds, or groups of compounds found in landfill gas sampled at six different landfill sites. Many of these trace compounds in landfill gas are recognised toxicants when present in air at concentrations which exceed established toxicity threshold limit values (TLVs) or the Occupational Exposure Standards (OESs) set by the Health and Safety Executive. Anyone coming into contact with landfiU gas is therefore potentially at risk from the toxic nature of the minor components, and under the Control of Substances Hazardous to Health Regulations (COSHH, 1988), landfill operators are legally responsible for the health of employees and are required to comply with OES s and exposure limits set by the Health and Safety Executive (HSE). 

Table 16.5 ACGIH Recommended Threshold Limit Values (TLV) for Ketones ...

The nor-isoprenoids most frequently found in flavors, a- and P-ionone (244) and (245), have a particularly high aroma value due to their characteristic odor qualities and their low threshold concentration (Table 3). Though both ketones had, for a long time, been... 

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