Odor-active components, assessment

Odor-active components in cheese flavor, many of which are derived from milk lipids, can be detected using GC-olfactometry (GC-O). GC-0 is defined as a collection of techniques that combine olfactometry, or the use of the human nose, as a detector to assess odor activity in a defined air stream post-separation using a GC (Friedich and Acree, 1988). The data generated by GC-0 are evaluated primarily by aroma extract dilution analysis or Charm analysis. Both involve evaluating the odor activity of individual compounds by sniffing the GC outlet of a series of dilutions of the original aroma extract and therefore both methods are based on the odor detection threshold of compounds. The key odourants in dairy products and in various types of cheese have been reviewed by Friedich and Acree (1988) and Curioni and Bosset (2002). 

GC-Olfactometry for the Assessment of Odor-Active Components of Essential Oils... 

GC-0 methods are commonly classified in four categories dilution, time-intensity, detection frequency, and posterior intensity methods. Dilntion analysis, the most applied method, is based on successive dilutions of an aroma extract until no odor is perceived by the panelists. This procedure, usually performed by a reduced number of assessors is mainly represented by CHARM (combined hedonic aroma response method) [67], developed by Acree and coworkers, and AEDA (aroma extraction dilution analysis), first presented by Ullrich and Grosch [68]. The former method has been applied to the investigation of two sweet orange oils from different varieties, one Florida Valencia and the other Brazilian Pera [69]. The intensities and qualities of their odor-active components were assessed. CHARM results indicated for both the oils that the most odor-active compounds are associated with the polar fraction compounds straight chain aldehydes (Cg-C,4), p-sinensal, and linalool presented the major CHARM responses. On the other hand, AEDA has... 

The response of vertebrates to olfactory stimulation is affected by previous experience but behaviour can be specifically affected by odours (pheromones) (4). The olfactory system has been shown to detect specific components within complex mixtures and analytical chemistry techniques have been used to identify these active components (5). We have assessed the application of these methods to the problems of agricultural odours in an attempt to develop techniques applicable to both slurries and air samples. The identification of the odorous components might allow specific treatment methods to be developed. In addition, the designation of a range of indicator compounds might be useful in practice for monitoring abatement of odour nuisances. 

In many ways, colour, which is a sensation, should be assessed visually. On analogy with the treatment of odorants, Hofmann73 has taken a crucial step in this area by defining a colour dilution factor (CD) and a colour activity value (CAV). CD is the factor required for any solution of a colorant x to be diluted to its colour threshold. CAVX is the ratio of the concentration of x (jug kg-1) to its threshold concentration (jug kg-1)- The colour contribution of a component colorant to the colour of a mixture can then be defined as... 

Small rodents depend on detection of a predator prior to actual contact. Thus, voles are sensitive to the scent of potential predators and respond to such odors without the necessity for other cues. In the wild, field voles Microtus agrestis) have been observed to avoid traps tainted with either weasel (Mustela nivalis) anal gland secretion or red fox (Vulpes vulpes) feces (Dickman Doncaster, 1984 Stoddart, 1976). Similarly, meadow and montane voles (M pennsylvanicus and M. montanus) were observed to avoid traps treated with the principal odiferous component of fox feces, 2,5-dihydro-2,4,5-trimethyl thiazoline (Sullivan, Crump Sullivan, 1988). The laboratory experiments discussed in the present chapter provided a quantitative assessment of locomotor activity levels following exposure to predator odor in laboratory-bred meadow voles. 

However, it should be taken into account that essential oils are mnch more active in the in vitro conditions than in in situ (e.g. in food and cosmetic) or in vivo (in patients) model systems. The effective content of individnal essential oil is nsn-ally too high to be acceptable for the application to food prodncts becanse of the intensity of aroma. In the last decade, the assessments of antibacterial and antifnn-gal activity of essential oils in prodnct model systems have been more and more numerous. Such research revealed synergistic or at least additive effects in the mixtures of essential oils or essential oil with other food additives (Bassole et al. 2010 Tajkarimi et al. 2010). This snggests that such mixtures could be used in order to diminish the odor of each individual component and improve the preservative properties. Essential oils therefore wiU continue to be indispensable natural ingredients and they may provide alternatives to conventional antimicrobial additives in food. 

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