Taste thresholds lactones

The flavor is described as green, fatty, dairy, lactonic (Chemisis, 1991). Siek et al. (1969) gave a taste threshold in water of 2.4 ppm. 

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). 

Caffeine and the quinic acid lactones listed in Table 21.13 are the bitter substances in the coffee drink. Accordingly, these lactones are almost exclusively responsible for the bitter note of a decaffeinated coffee drink (Table 21.13). Although the concentrations of the lactones III-VII, IX and X in the drink are lower than their threshold concentrations (cf. Table 21.13), they still additively contribute to the bitter taste (cf. 5.1.2 additive effect). 

In order to determine the taste modulating activity of the identified compounds, triangle tests were performed with the purified compounds dissolved in water (for intrinsic taste) as well as in a model broth solution (for taste modulatory activity), respectively. None of the compounds 1-5 showed any intrinsic taste up to a maximum concentration of 1000 pmol/kg, but all these creatinine derivatives imparted taste modulating activity in model broth by enhancing its thick-sour, brothy taste. The lowest threshold concentration of 76 pmol/kg was found for 4-hydroxy-2-A-(l-methyl-4-oxoimidazolidin-2-ylideneamino) butanoic acid (3), whereas the highest threshold level of 489 pmol/kg was determined for 4-hydroxy-2-77-(l -methyl-4-oxoimidazolidin-2-ylideneamino)pentanoic lactone (4) (Table 1). 

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