Organoleptic importance

Naturally occurring organoleptically important lactones are mainly saturated and unsaturated 7- and -lactones, and to a lesser extent macrocyclic lactones. The occurrence of these types of lactones reflects their ready formation from natural acyclic precursors. 

The organoleptic importance of alkylthiazoles was already recognized in 1966 (Arnold et al.) when they were isolated for the first time in food aromas. They play an important role, for instance, in the flavors of roasted cocoa beans, in roasted peanut flavor (Ho et al., 1983b) and in cooked beef flavor (Chang et al., 1977). They were found for the first time in coffee by Stoll et al. (1967) who identified 2-acetyl-4-methylthiazole (M.26) and 2-propionyl-4-methylthiazole (M-27). 

The probable organoleptic importance of dihydropyrazines which temporarily exist in freshly roasted coffee but are too unstable to be extracted, separated and isolated during analytical studies, has been frequently invoked. Bondarovich et al. (1967) observed that some of these intermediates in the synthesis of pyrazines possessed definite roasted peanuts or popcorn character. 

The chemistry of sulfur compounds in foods is very complex and continues to be extensively studied. Both cooked and uncooked foods contain organoleptically important sulfur-containing compounds. Conversely, the off-odors of numerous foods have been attributed to sulfur compounds. In addition to their sensory properties, recent work has been increasingly geared towards other functional properties of these compounds, especially antioxidant, antimicrobial, and anticarcinogenic effects. These areas will, no doubt, continue to be the subject of research for years to come. 

These relative values demonstrate the organoleptic importance of trace components of high potency in an aroma complex. The analyst frequently reaches the limit of detectability for volatile substances. The most sensitive method known today consists in the direct coupling of a gas chromatograph with a mass spectrometer. This method allows the analytical detection of 10 mole of a single component in a mixture (43, 544). 

Thymol (169) is found in a number of species, mostly from the Thymus, Ocimum, and Monarda families. It takes its name from thyme (T. vulgaris) of which it is an organoleptically important component. The levels present vary widely not only from species to species, but also from plant to plant within a species. As it is a phenol, it can be extracted from herb oils using aqueous sodium hydroxide and subsequent acidification. Such techniques were used to produce thymol in the past, particularly from thyme, oregano, and basil. Material isolated in this way tended to contain some carvacrol (213). This is a disadvantage as the medicinal, phenolic, and tarry odor of carvacrol spoils the sweeter, herbal, and medicinal odor of thymol. Since thymol is easily prepared, as described above under menthol, the modem supply is entirely synthetic, mostly from Symrise. The major use for thymol is as an intermediate for menthol production. 

This is particularly important since current flavor research seems to be less directed to identification for the sake of adding to the numbers of the compounds in the knowledge base, and more to alternative reasons. At the present time it appears one purpose is characterization of components of organoleptic importance. Three techniques for gas chromatographic individual component assessment are in vogue aroma extraction dilution analysis (AEDA), calculation of odor units, and CharmAnalysis (see Chapter 12). Another purpose of flavor research is to analyze products and to perform flavor stability studies. 

Figure 21 shows a comparison of the neutral cheese fractions isolated not only by SAFE but also by the SDE technique. There were differences in both the qualitative and quantitative composition. Many heat-induced alterations of the aroma profile in the SDE sample were observed (data not presented). Identification of cheese volatiles was based on GC/MS. We found, based on our spectroscopic investigation of the acidic fraction, that the SAFE technique was more effective in extracting less volatile and polar constituents such as 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 4-hydroxy-5-methyl-3(2H)-furanone, and 5-ethyl-4-hydroxy-2-methyl-3(2H)-furanone. As a result, it should be possible to quantify these organoleptically important trace constituents by special techniques—e.g.,... 

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