Isothiocyanate odor threshold value

This study focuses on the determination of the characteristic odorants of wasabi in comparison with those of horseradish by calculation of the logarithmic ratio between the concentration of isothiocyanate and its odor threshold value. The relationship between the yields of the isothiocyanates formed by the action of wasabi myrosinase and the conditions of hydrolysis are presented. 

The remarkable difference between wasabi and horseradish was the concentrations of the oj-alkenyl isothiocyanates (5-8) (Table I), the aryl isothiocyanates (10) and (11) (Table I), and the oj-methylthioalkyl isothiocyanates (12-14) (Table I). The odor threshold values of the o-alkenyl isothiocyanates (5-7) were lower than the other isothiocyanates. In addition, these oj-alkenyl isothiocyanates had about half the value of that of allyl isothiocyanate (2) (Table I). The alkyl isothiocyanates (1, 3 and 4) (Table I) possessed a chemical odor but no pungent note. Hence, it seems that those compounds make relatively small contributions to the characteristic odor of wasabi and horseradish. The other isothiocyanates except for( 1, 3 and 4), however, had pungent and/or radish-like odors. 

Figure 1. Logarithms of the ratios of the concentrations to the odor threshold values (log(C/T)) (top) and exponents (n) of the FD factor 2", (bottom) for the isothiocyanates versus their retention indices (RI).

The volatile components of both wasabi and horseradish formed by the hydrolysis of thioglucosides with myrosinase are known to possess a strong pungency. The difference between wasabi and horseradish is a green odor. The ratio of the concentration to the odor threshold, C/T, is called the aroma value. Sensory response is logarithmically proportional to the amount of stimulus. In this study, the log of the aroma values, log(C/T), for 14 isothiocyanates have been used instead of their conventional aroma values. co-Alkenyl isothiocyanates, which possessed higher log(C/T) values than those of horseradish, contributed to the green odor of wasabi. Furthermore, the yields and the values of log(C/T) of the isothiocyanates catalyzed by myrosinase were affected by pH and temperature. 

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See also in sourсe #XX -- [ ]

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