Does saponin in quinoa really embody the source of its bitterness?

While it is widely reported that saponins are the main source of the bitter taste in quinoa, this work found that some saponin compounds in quinoa husks elicit an umami response. The saponins were analyzed qualitatively and quantified by mass spectrometry (UPLC-MS). Two quinoa saponin compounds RT 46 (3-O-β-d-glucopyranosyl-(1 → 3)-α-l-arabino-pyranosyl-phytolaccagenic acid 28-O-β-d-gluco-pyranosyl), and RT 53 (3-O-β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranosyl-28-O-hederagenin) were isolated from quinoa husks through separation and purification. According to eletronic tongue, the main taste response for those compounds was umami. It was found that the two quinoa saponins could bind to sweet and umami receptors. Besides saponins, various flavonoids and polyphenols also appeared in the UPLC-MS spectrum of crude saponins. The electronic tongue and sensory evaluation revealed that flavonoids and polyphenols showed obvious bitterness and astringency at very low concentrations. The study inferred that flavonoids and polyphenols are the main compounds that generate quinoa's bitter taste.