EEG and fNIRS evidence for brain responses to three tannins: implications for astringency surface sub-quality in red wine

The astringency surface sub-quality is pivotal to red wine perception, yet its neural bases remain unclear. The approaches of non-invasive neurophysiological techniques, sensory analysis, liquid chromatography-mass spectrometry (LC-MS) analysis, and molecular docking were applied to examine the astringency surface sub-quality responses to three tannins—tannic acid, grape tannin and wine tannin—standardized to equivalent astringency intensity. The results showed that the three tannins at iso-intensity evoked distinct brain activity and sensory responses (wine tannin > tannic acid > grape tannin). The electroencephalography (EEG) results showed that frontal activation was significantly higher than in other regions, with differential delta-band power, while functional near-infrared spectroscopy (fNIRS) revealed corresponding changes in oxygenated hemoglobin across different frontal cortical regions, most prominently at channel 6 in the ventromedial prefrontal cortex. LC-MS analysis of tannins indicated that higher levels of tannin oligomers, polymeric pigments and free anthocyanins were associated with finer astringency sub-quality and stronger neurophysiological responses. By establishing a clear link between chemical composition and neural activation, this investigation demonstrates the efficacy of using neurophysiological measures as a robust, objective tool to complement and refine traditional sensory evaluation of wine.