Dicaffeoyl polyamine derivatives from bitter goji: Contribution to the bitter taste of fruit

Although the bioactive compounds in goji have been thoroughly identified and quantified, little information is available on the bitter compounds in the berries, and no systematic works on the substances responsible for their bitterness have been performed. Herein, the substances contributing to the bitterness of berries were isolated and purified from bitter-tasting goji by the combined use of column chromatography and high-pressure liquid chromatography (HPLC). The bitterness of the isolated compounds was evaluated using a biosensor with immobilized rat taste-bud tissues. The structures were elucidated via comprehensive mass spectrometry (MS) and nuclear magnetic resonance (NMR) analyses. Seven spermine or spermidine alkaloids were identified, including four new compounds (lyciamarspermidines A and B and lyciamarspermines A and B). The intensities of the bitterness levels of the isolated compounds differed with the number of glucose substituents. These isolated compounds all contribute to the bitterness of goji. The results of this study provide opportunities for the further investigation of the bitterness of goji.