The bitterness in lulo (Solanum quitoense Lam.) fruit is increased during processing (juicing or drying). To identify the bitter-active compounds, the ethanolic fruit pulp extract was subjected to RP-18 solid-phase extraction, and then sensory-guided fractionated by HPLC. Two spermidine derivatives, N(1),N(4),N(8)-tris(dihydrocaffeoyl)spermidine and N(1),N(8)-bis(dihydrocaffeoyl)spermidine, were isolated and their structures confirmed by analysis of their HPLC-ESI/MS and (1)H and (13)C NMR data. The N(1),N(4),N(8)-tris(dihydrocaffeoyl)spermidine was synthesized and used as an authentic sample to unequivocally confirm the structure of this compound and to quantitate it in both fresh and dried fruit. In silico analyses demonstrated that spermidine derivatives identified in lulo pulp exhibited a strong ACE-I (angiotensin I-converting enzyme) inhibitory activity. Subsequently, these results were confirmed by in vitro analyses and showed the potential use of lulo fruit pulp as an ingredient of functional foods related to the prevention of blood hypertension.
Keywords: ACE-inhibitory activity; Solanaceae; antihypertensive activity; bitterness; molecular docking.