Prediction of perceived astringency induced by phenolic compounds Erminio Monteleone a, * , Nicola Condelli a , Caterina Dinnella a , Mario Bertuccioli b a Dipartimento di Biologia DBAF, Universit a degli Studi di Basilicata, Campus di Macchia Romana, 85100 Potenza, Italy b Dipartimento di Biotecnologie Agrarie, Universit a degli Studi di Firenze, Via Donizetti 42, Firenze, Italy Received 21 July 2003; received in revised form 8 June 2004; accepted 8 June 2004 Available online 6 July 2004 Abstract A method which can be used to estimate perceived astringency due to polyphenolic compounds is presented here. Thirty subjects were selected on the basis of them having similar salivary flows and they were trained to rate the perceived astringency of tannic acid and grape seed extract solutions. A scale of phenolic compound concentrations ranging from 0 to 3.2 g/L was selected in order to obtain an experimental curve describing the perceived intensity of the sensation. The same astringent solutions were added to a mucin solution in conditions resembling those present in the oral cavity. The formation of polyphenol–protein complexes was measured on the basis of the increasing turbidity of the reaction mixture and was expressed in terms of nephelometric turbidity units (NTU). Experimental curves describing NTU vs polyphenol concentration were obtained. Predictive models of astringency intensity vs NTU were produced. The predictive capacity of the models was checked by comparing the measured and predicted intensities of a set of samples prepared at phenolic compound concentration level varying from 0.94 to 2.13 g/L. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Polyphenols; Proteins; Mucin; Sensory evaluation; Astringency; Nephelometry 1. Introduction The sensation of astringency on the human palate has been defined as a complex group of sensations involving dryness of the oral surface and tightening and puckering sensations of the mucosa and muscles around the mouth (Gawell, Oberholster, & Francis, 2000; Lee & Lawless, 1991). It is generally accepted that astringent com- pounds form complexes with salivary proteins, resulting in their aggregation and/or precipitation and the loss of their lubricating properties (Kallithraka, Bakker, & Clifford, 1998). These interactions have led to the theory that astringency is, at least initially, due to de-lubrica- tion via the removal of slippery coating on the oral surface. Mechanoreceptors stimulation might contribute to this sensation (Thorngate & Noble, 1995). It has also been suggested that other factors such as the presence of precipitate on the tongue and on the soft palate might contribute to the sensation. Moreover, traces of astrin- gent substance remaining in solution might interact with taste receptors and might stimulate the classical taste pathways and contribute to the overall sensation (Critchley & Rolls, 1996). The formation of soluble complexes of polyphenol–protein able to modulate sal- ivary viscosity has also been proposed as a factor affecting astringency perception (Clifford, 1997). The reintroduction of various sort of lubricants such as gums, polysaccharides and proteins alleviates astrin- gency after it has been elicited (Brannan, Setser, & Kemp, 2001; Colonna, Adams, & Noble, 2004). A recent study pointed out the importance of indi- vidual saliva flow and composition variations in influ- encing the intensity of the perceived sensation (Horne, Hayes, & Lawless, 2002). The intensity of perceived astringency plays a key role in determining the acceptability of various food prod- ucts and is produced by a variety of oral-chemical stimuli such as aluminium salts, acids and polyphenols. Several studies have been performed to mimic the pol- yphenol–protein reaction which takes place in the oral cavity in order to produce chemical–physical responses that can be correlated to the astringency inducing capability of compounds under consideration. The in * Corresponding author. Tel.: +39-971-205694; fax: +39-971- 205693. E-mail address: monteleone@unibas.it (E. Monteleone). 0950-3293/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodqual.2004.06.002 Food Quality and Preference 15 (2004) 761–769 www.elsevier.com/locate/foodqual