pH dominates the temporal perception of astringency sub-qualities and saliva friction response - A study under iso-pH and iso-titratable acidity conditions in model wine

Astringency is a multidimensional perception comprising sensorily distinct sub-qualities. In wine production, attaining balanced astringency is critical to producing premium products. Although tannin has been viewed as the primary cause of wine astringency through colloidal interactions with salivary proteins and the modification of lubricating salivary film, how acids act in similar roles remains underexplored. This study aimed to address this gap by investigating the impact of acids (malic, lactic or tartaric acids) on the wine astringency profile under iso-pH and iso-titratable acidity (TA) conditions. Samples were sensorily evaluated with a progressive profiling method and tribologically tested to determine their impact on saliva lubrication. The results indicated that acids, independent of tannin, can elicit all astringency sub-qualities, and specifically that the pucker sub-quality is closely associated with low pH. pH had a more dominant impact on the temporal sensory scores than TA. At iso-TA, the score of all astringency sub-qualities was solely dependent on pH; at iso-pH, lowering TA increased the score of drying and roughness. The tribology results demonstrated that the rate of saliva friction increase was significantly correlated with pH but not TA. We propose that, during oral processing, pH dominates the process of saliva protein deformation, removal of lubricating pellicle, increased oral friction and astringency perception. However, high TA encourages saliva flow which neutralises oral pH and restores lubrication, counterbalancing the low pH's contribution to astringency. Wine production processes could leverage this knowledge by implementing various acid-modification techniques to achieve the desired level of astringency quality of wines.