Phytosterols in onion contribute to a sensation of lingering of aroma, a koku attribute

We aimed to examine the substance in a precipitate of heat-treated onion concentrate (HOC) that contributes to a sensation of lingering of aroma, a koku attribute induced by the sensing of richness and persistence in terms of taste, aroma and texture. Adding precipitate, separated from HOC, to consommé enhanced the lingering sensation of aroma in the consommé more than adding the supernatant from HOC. After the precipitate was washed with hot water and ethanol its enhancing effect disappeared. Analysis of the HOC precipitate showed that it contained phytosterols, such as beta-sitosterol and stigmasterol. Tests of binding to aroma compounds showed that both sterols, as well as the washed precipitate, were able to bind methyl propyl disulfide and N-hexanal. Thus phytosterols in the HOC precipitate seemed to bind and hold the aroma compounds and gradually release them, inducing a lingering sensation of aroma under the koku concept during consumption.