*Chemistry and Biochemistry of Winemaking, Wine Stabilization and Aging*

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**145**

**Chapter 7**

**Abstract**

**1. Introduction**

food and beverage [6].

utility of the hide's physical properties [7].

Astringency

Salivary Protein-Tannin

*Alessandra Rinaldi and Luigi Moio*

Interaction: The Binding behind

Interactions between salivary proteins and tannins are at the basis of one of the main mechanisms involved in the perception of astringency. Astringency is a tactile sensation evoked in the mouth by plant polyphenol-derived products, such as red wine. It is generally recognised that tannins can provoke negative sensations such as shrinking, drawing, or puckering of the epithelium. On the other hand, the astringency of some red wines can be felt as pleasant mouth feelings of richness, fullness, mouth-coating, and velvet in the mouth. In this chapter, an overview of the research concerned with molecular and sensory mechanisms of astringency was updated. Because of many variables influence the perception of astringency, several methods have been developed to measure the intensity of the sensation. In this context, different indirect assessments were critically evaluated considering the pros and contras and correlated with sensory analysis. We focused the attention on the saliva precipitation index (SPI), based on the binding and precipitation of human saliva with grape and wine tannins, because it has been widely used for many applications in winemaking. A current great challenge is to have an *in vitro* measurement of astringency able to provide information on the fate of wine, from grape to bottle.

**Keywords:** astringency, salivary proteins, polyphenols, precipitation, methods

The interaction between plant tannins and macromolecules such as proteins is at the basis of many processes involved in the industry, ecological and agricultural systems [1–3], and food and beverage sensory characteristics. The common factor is the binding between macromolecules and tannins that lead to: (i) the conversion of an animal hide into the leather (tanning or *tannage*); (ii) the plant defence strategies against pathogens [1, 4]; (iii) reduced palatability of high tannin feedings to both terrestrial and marine herbivores and then a reduced interference in the process of digestion [2, 5]; (iv) the perception of astringency in tannin-rich

In the tanning process, the tannins bind to the hide's matrix, which is composed primarily of the protein collagen ordered in microcrystalline helical units. The purpose of *tannage* is primarily to increase the hydrothermal stability of the structure of collagen, secondarily to increase biological inertness, and finally, to improve the
