Abstract
The relationship between chemical structure and odor characteristics of aroma compounds is interesting in terms of establishing a fundamental understanding and, in the long term, a perspective for the prediction of odor qualities and intensities of unknown compounds; on the other hand, such studies provide a useful tool to analytically elucidate compounds that are exceptionally potent odor contributors to a specific smell. In this respect, a broad knowledge of compounds with regard to their odor threshold and smell specificities compiled in a comprehensive odor library would drastically simplify the chemoanalytical process in identifying aromas and smells. Whereas numerous odor-active substance classes have been investigated intensively, such relationships and fundamental data have hitherto not been established for volatile phenols. In this study, a homologous series and isomers of 30 volatile phenols, including monoalkylated phenols and di- and trimethylphenols, were evaluated by determining their aroma attributes and their odor detection thresholds in air. The investigation demonstrates that the odor qualities, among them leather-like, horse stable-like, and medicinal, as well as the respective threshold values clearly depend on the arrangement of the alkyl substituents at the phenol ring. In particular, phenols with monoalkyl groups in the meta-position were found with very low odor detection thresholds of <1 ng/L air. A comparison of some selected phenols and their corresponding toluenes, which were found to be almost odorless, showed in addition that the phenolic hydroxyl group is obviously an important factor for the odor characteristic of this substance class.
Highlights
The evaluation of odor-active compounds within the volatile fraction of a food results in the identification of a characteristic set of substances responsible for the overall food aroma
One example is the very potent grapefruit juice odorant 1-p-menthen-8-thiol. The concentration of this thiol in grapefruit juice has been determined to be as low as 0.01 lg/L (10 ng/L), this still has a significant contribution to grapefruit aroma due to its extremely low odor threshold of 0.0001 lg/L water (Buettner and Schieberle 2001b)
The present study aims to close this gap by providing a systematic elucidation of the relationships between chemical structure and odor quality, as well as odor threshold, of homologous series of monoalkylated and isomeric di- and trimethylated phenols
Summary
The evaluation of odor-active compounds within the volatile fraction of a food results in the identification of a characteristic set of substances responsible for the overall food aroma. Many of these compounds occur in numerous food products and are characterized by high aroma activities. The concentration of this thiol in grapefruit juice has been determined to be as low as 0.01 lg/L (10 ng/L), this still has a significant contribution to grapefruit aroma due to its extremely low odor threshold of 0.0001 lg/L water (Buettner and Schieberle 2001b). A preponderant number of odor-active food compounds have been identified with threshold values in the parts per billion range
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