| Abstract
| - The interaction of polyphenols (tannins) with proline-rich proteins (gelatin) has been studied usingan automated flow injection system with Fourier transform infrared spectroscopic detection to gain insightinto chemical aspects related to astringency. In the perception of astringency, a major taste property in redwines and other beverages such as beer, tea, or fruit juices, an interaction between proline-rich salivaryproteins and tannins present in the sample takes place. To study this interaction, agarose beads carryinggelatin (a proline-rich protein) were placed in the IR flow cell in such a way that the beads were probed bythe IR beam. Using an automated flow system, we injected samples in a carrier stream and flushed overthe proteins in a highly reproducible manner. Simultaneously, any retardation due to tannin−proteininteractions taking place inside the flow cell was monitored by infrared spectroscopy. Tannins of differentsources (grapes, wooden barrels, formulations used in wine making) were investigated, and their flow-through behavior was characterized. Significant differences in their affinity toward gelatin could be observed.Furthermore, because of small but characteristic differences in the IR spectrum, it is possible to distinguishcondensed from hydrolyzable tannins. Nonastringent substances such as alcohols, sugars, and acids didnot show retention on gelatin. The selectivity of the flow-through sensor was also demonstrated on theexample of red and white wine. In contrast to white wine, where no interaction could be observed, in redwine a major interaction of the red wine tannins was found.
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