Sub-threshold effects on the perceived intensity of recognizable odorants: The roles of functional groups and carbon chain lengths

Sub-threshold effects were studied in binary and tertiary mixtures comprising a panel-recognition-concentration odorant and sub-threshold odorant(s). Sub-threshold condition was maintained by controlling the sub-threshold concentration as percentages of subjects' individual detection threshold. The perceived intensities (overall intensity and several descriptors) of recognizable odorants were rated using magnitude estimation.; Sub-threshold suppression was common and concentration independent in mixtures comprising odorants with different functional groups. Suppression was observed at the lowest sub-threshold concentration tested (30% level). At sub threshold concentrations, acetic acid suppressed the perceived intensity of acetaldehyde and ethanol but not vice versa. Acetaldehyde and ethanol, however, suppressed each other when one was at sub-threshold concentrations in binary mixtures. Enhancement was observed in tertiary mixtures containing acetaldehyde at panel recognition concentration and was dependent on sub-threshold concentrations of acetic acid and ethanol.; In mixtures that contained aliphatic acids with different carbon chain lengths (acetic acid, propanoic acid and n-butanoic acid), sub-threshold enhancement and suppression depended on concentrations and molecular similarity of mixture components. Sub-threshold effects were not observed when the acids were two carbon-atoms different. 50% and 70% sub-threshold levels caused subthreshold enhancement; however, higher concentrations caused decrease in intensity. Sub-threshold suppression was observed in mixtures containing n-butanoic acid as a recognizable odorants with propanoic acid at a 10% level in a binary mixture and acetic acid and propanoic acid in a 30%-30% combination in the tertiary mixture.