Phenolic Profiles and Antitumor Activity against Colorectal Cancer Cells of Seeds from Selected Ribes Taxa

Seeds from several Ribes taxa were surveyed for phenolic compounds and in vitro antiproliferative activity against HT-29 colorectal cancer cells. Total phenolic compounds were analyzed through the Folin–Ciocalteu procedure, while LC coupled to a single mass spectrometer (MS) Orbitrap using an electrospray interface (ESI) was performed to determine the phenolic profiles. Antitumor effects were established using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Total phenolics ranged from 11.4 in R. alpinum to 94.8 mg of caffeic acid equivalents (CAE)/g in R. nigrum ‘Koksa’. Concerning phenolic compounds, four were hydroxylated benzoic acids, four cinnamic acid derivatives, eight flavonoids, and nine flavonoid glycosides. The growth inhibition against HT-29 cancer cells was exercised much better by R. nigrum ‘Koksa’ and Ribes ‘Erkeeni’ (GI50 37 and 42 µg/mL). All Ribes extracts, except for R. nigrum ‘Hara katarlik’, showed higher activity than R. rubrum (GI50 at 72 h: 99 µg/mL). Interestingly, the extract from Ribes ‘Erkeeni’, which exhibited high bioactivity, contains all detected phenolic compounds, unlike R. nigrum ‘Koksa’, which lacks only populnin. Therefore, the high bioactivity found for such extracts could be due to a synergy of all detected compounds. This work constitutes a comprehensive action for expanding knowledge on the phenolic profiles and antitumor activity of GLA-rich Ribes seeds.