Gerald F. Russell

Chemoreception and perception of the bitterness of isohumulones

Psychophysical experiments were conducted to determine whether isohumulones share a common receptor mechanism with other bitter compounds, and whether parotid saliva flow affects perception of their bitterness. Findings from a study of inter-individual differences in sensitivity to 23 sweet and/or bitter compounds among 25 subjects using the time-intensity (TI) method suggest that isohumulone and tetrahydroisohumulone may share a common receptor mechanism with other bitter compounds except those with the thiourea moiety. Isohumulone and tetrahydroisohumulone displayed a unique dome-shaped TI profile. The bitterness of the two compounds took longer to develop, but it lasted as long as for other bitter stimuli. In a study of the relation between perception of bitterness in beer and parotid saliva flow in 20 young adults, no significant difference was found among the mean saliva flows triggered by 0, 15 and 30 mg/L of isohumulones added to beer, and no significant correlation was found between saliva flow and maximum intensity or total duration of bitterness.

Dynamic Headspace Analysis of Fresh Tomato Juices

The methods used to isolate volatile compounds for GC analyses can cause profound effects on the quantitative and qualitative composition of the injected sample, and exert a great influence in the resultant bioactivity of volatiles. Especially with plant tissues like tomatoes, the isolation of volatile constituents using classical methods may yield results which are not representative of the chemicals present in the natural material. Headspace sampling methods may be advantageous in capturing the same volatile compounds emitted from tomatoes that are detected by the human nose. This study utilized an extremely sensitive dynamic headspace sampling with thermal desorption method to determine volatile components of fresh tomato juices. The method proved very sensitive for the isolation of tomato volatiles and concentrations of flavor compounds were much greater than related literature studies.