The gold standard for evaluating the flavor properties of foods or beverages is a human sensory panel, but such studies are time-consuming, noisy, and expensive. To reduce the need for sensory panels, food chemists often develop assays that characterize key sensory attributes of foodstuffs. For example, astringency (i.e., the tactile sensation of stickiness or friction in the mouth) is a key contributor to the sensory properties of many beverages, including cranberry juice, wine and cocoa. Astringency is often due to the presence of plant-derived condensed tannins (CT). CT can form non-covalent linkages with proteins, including lubricating salivary proteins and oral tissues, which is believed to account for their astringent flavor. Students can perform a crude physiochemical assay for astringency by sipping and spitting solutions of cranberry juice extract, and then developing correlations between their sensory experience and the amount of precipitate formed in their expectorate (or, more crassly, the size of the ‘loogie’). The sip-spit assay can be evaluated for standard figures of merit (reproducibility, linearity, robustness across analysts). Students can then be challenged to devise ways to make the assay more quantitative and robust, e.g. by using a standardized protein solution to precipitate proteins, by weighing the precipitate, or by using spectrophotometry to selectively measure the CT component.

Sip, spit, repeat: Learning the basics of assay development through evaluations of astringency in beverages

251st National Meeting (2016)

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