Flavor threshold, description

Butanoic acid has a powerful, penetrating, diffusive sour odor, reminiscent of rancid butter (Arctander, 1967). It is in the list of potent odorants in raw arabica with a sweaty odor description (Czerny and Grosch, 2000). An odor threshold of 240 xg/l (0.24 ppm) in water is quoted by Teranishi (1971). A flavor threshold of 6.8 ppm in water is given by Patton (1964), and 6.2 ppm by Siek et al. (1969). 

Literature information about the sensory properties for nearly 450 Maillard reaction products has been compiled in a survey. It includes qualitative aroma and flavor descriptions as well as sensory threshold values in different media for the compounds, classified according to their chemical structure. 

The low odor threshold (0.1 pg/kg water) of this compound and its odor description as "popcorn-like" (27) agrees with its strong crusty character. Furthermore, the statement of Buttery et al. (27) that "2-acetyl-l-pyrroline seems to be the most potent of the cracker-like group of odor compounds" (which includes 3, 5 and 7 in Figure 1) underlines its importance for the flavor of the white bread crust. 

The sensory properties of nearly 450 volatile Maillard reaction products and related compounds have been compiled (45). The review includes quantitative aroma and flavor descriptions, as veil as sensory threshold values for different media, classified according to chemical structure. 

Pyrazines. In the thirties, the attention on pyrazines was focused on its industrial role in dyes, photographic emulsions and chemotherapy. Its importance in life processes was indicated in its derivative, vitamin B2 (riboflavin, 6,7-dimethyl-9-(l -D-ribityl isoalloxazine). Later,in the midsixties, it was identified in foods and its contributions to the unique flavor and aroma of raw and processed foods attracted the attention of flavor chemists Pyrazine derivatives contribute to the roasting, toasting, nutty, chocolaty, coffee, earthy, caramel, maple-like, bread-like, and bell pepper notes in foods. The reader is referred to the reviews on Krems and Spoerri (88) on the chemistry of pyrazines, and the review of pyrazines in foods by Maga and Sizer (89, 90) Table XVI summaries sensory description and threshold of selected pyrazines. 

Pangborn, R.M., A critical review of threshold, intensity and descriptive analysis in flavor research, in Flavor 81, Schreier, P., Ed., Walter de Gruyter, Berlin, 1981, p. 1. 

The flavor description is maple, fenugreek, burnt (Chemisis, 1968). The odor description is very strong caramel-like, stronger than D.68, D.69, D.73 and D.87 (Shaw et al., 1968) sweet, burnt at 1 ppm in water, with an odor threshold of 0.02 ppm in water (Nishimura and Mihara, 1990). 

Its excessive concentration contributes to the perception of a fruity, apricot off-flavor character. For the (S)- enantiomer, Karl et al. (1992) gave the description of ethereal, sweet, non-specific, becoming pleasantly apple-like when diluted. The flavor of this isomer was described as fruity, ethereal, strawberry, similar to that of the racemic compound (Chemisis, 1995). The odor threshold given by Flath et al. (1967) was 0.1 ppb, 0.006 ppb [(+)-( )- ] by Takeoka et al. (1995) and 0.5 xg/kg cellulose by Czerny and Grosch (2000). 

This lactone is the flavoring compound formed by the aging of a-ketobutyric acid (Sulser et al., 1967). The flavor is described as malt, molasses, maple, burnt sugar (Chemisis, 1965), with a strong seasoninglike aroma at a concentration of 0.1 ppm and a taste threshold of 1-5 ppb for Sulser et al. (1972). Manley et al. (1980) reported a maple-like, remarkably persistent curry-like odor and wondered if the enolization or the instability of the compound could be responsible for the two notes. It is a potent odorant of roasted powder and brew of arabica coffee with odor descriptions similar to those of G.12, and an odor threshold of 2-4ng/m , air (Blank et al., 1992a,b), of 7.5 ppb in water (Semmelroch et al., 1995). 

The authors gave an odor threshold of 0.01 ppb in water and the same aroma description as for the methylthio compound 1.123. At a concentration of 1 ppm, it has a vitamins-thiamine, meaty, roasted, alliaceous flavor (Chemisis, 1998). 

As noted above, there is substantial information available describing the sensory properties of aroma compounds. The classic references in this respect were not mentioned above but are the works of FenaroU [18] and Arctander [ 19]. In addition, most suppliers of aroma chemicals provide a characterization of their product. However, those directly concerned with CTeating flavoring compositions have to develop their own characterizations based on their personal evaluation of these chemicals. The descriptions provided in the literature are based on an individual s vocabulary, experience, and perception which vary as widely from individual to individual as do the sensory threshold data. Thus, those coming into this field must keep records of their own evaluations of odor and flavor characters of all aroma chemicals. This whole process is what differentiates one flavorist s creation from another. 

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