Astringency perception

Interactions between tannins and proteins have been extensively studied (Hager-man 1989 Haslam and Lilley 1988 Haslam et al. 1992), owing to their role in haze formation, astringency perception, and nutritional and anti-nutritional effects resulting from inhibition of various enzymes and reduction of dietary protein digestion. Other effects include reduced adsorption of /3-casein at the air-liquid interface in the presence of epigallocatechin gallate with potential consequences on foam properties (Sausse et al. 2003). 

The astringency sensation is felt differently by different tasters (Gawel et al. 2001) probably due to differences in individuals saliva, namely its protein composition (Lesschaeve and Noble 2005 Horne et al. 2002). Recently, a study concerning the characterization of basic PRPs in thirteen normal adults has demonstrated that the protein IB9 was only detected in nine adults saliva, while IB7 was not detected at all (Messana et al. 2004). The salivary flow rate was also described as a factor that varies between subjects and can affect astringency perception (Lesschaeve... 

A sensory study based on an incomplete factorial design allowed to demonstrate that astringency of procyanidins was reduced in the presence of rhamnogalaturonan II added at levels encountered in wine but was modified neither by anthocyanins nor by the other wine polysaccharides (mannoproteins and arabinogalactan proteins). Increase in ethanol level resulted in higher bitterness perception but had no effect on astringency. 

Noble, A.C., Factors influencing perception of bitterness and astringency in foods and beverages, in Polyphenols 98. XVIXe Journees Internationales Groupe Polyphenols, INRA Editions, France, 1998,... 

The following chapter (G2) covers the measurement of acid tastants, i.e., chemicals responsible for the acid and sour taste as well as the perception of astringency. unitgu presents methods for potentiometric and colorimetric titration of acid tastants, and unit... 

F Bitter, astringent O Warm-herbaceous, winy-ethereal remotely resembling Hungarian chamomile (matricaria oil). A natural sweetness common similarity to hay, caramel, tobacco, etc. often perceptible F Sweet, herbaceous-hay-like, mildly tobacco-like F Bitter... 

Indeed, after a maturation period of 18 months, no significant differences were seen between the wines obtained without the yeast inoculums, either if they were aged in vinsantaia or at a constant temperature of 18 °C, except for the honey character and the color intensity. Similarly, also inside the cluster of wines obtained with both the yeast inoculum and the addition of madre there were no differences found in the perception of individual sensory attributes. However, the wines from the yeast-inoculated fermentation with the addition of madre were perceived to be more acidic, astringent, bitter, and viscous than the non-inoculated wines when they were aged in the cellar at constant temperature (18 °C). In contrast, there were no significant differences among the wines aged under the traditional conditions (vinsantaia). 

The complexities and interaction of composition on the quality perception of vermouth is illustrated with wild-apricot-based vermouth (Figs. 8.5-8.7). It shows that sweetness, flavor, and astringency are preferred at a sugar content of 8%, whereas body, appearance, and aroma were preferred at 12% sugar (Fig. 8.5). Body, flavor, aroma, and total acidity were scored better at an alcohol content of 19% (Fig. 8.6). The spice concentration preferred for volatile acidity, total acidity, flavor, and bitterness was 5% (Fig. 8.7), whereas body, sweetness, appearance, and astringency were preferred at a 2.5% level (Joshi et al, 201 la,b). 

Among polyphenolic compounds, two types of flavonoids, the anthocyanins and flavanols (i.e., catechins, proanthocyanidins, condensed tannins), are particularly relevant to the quality of red wines, as they are key compounds for color definition and astringency. Other flavonoids such as flavonols may have some influence on color and bitterness, although they are present in red wines in much lower amounts. Phenolic acids and hydrolysable tannins, released from barrel wood, may also have an influence on wine taste and color, and hydroxycinnamoyl derivatives from grape must are involved in the oxidative browning of white wines together with flavanols. Besides, some of these perceptions may be modified by other sensory characteristics (e.g. sourness, sweetness) related to other wine components (Preys et al. 2006). 

According to Noble and coworkers, seed tannins are perceived as rather bitter at low concentrations, but astringency takes over as the concentration increases (7,8). Otherwise, in apple ciders, hard tannin perception has been ascribed to bitterness (6). Nevertheless, in the Cabernet franc wines studied, low proanthocyanidin content appeared associated with soft tannins. Such discrepancy may be due to the particular composition of wine tannins, including prodelphinidins and various tannin-like structures e.g. oxidation products, ethyl-linked tannin polymers, anthocyanin-tannin adducts...), in addition to seed tannins. 

Red wines are characterized by bitterness and astringency, whereas white wines occasionally are bitter but seldom are astringent. In wine, both attributes are primarily elicited by the flavonoid polyphenolic compounds, which have been reviewed extensively elsewhere (i- i). In this chapter, attention will be focused on the most recent investigations of factors which influence perception of bitterness and astringency. 

Astringency is a tactile sensation, which is often described as a puckering, rough or drying mouthfeel. The mechanism of its perception is unknown, although it is probably mediated by touch or mechanoreceptors 4). Chemically, astringents have been defined as compounds which precipitate proteins. For water soluble phenols, this has been reported to require molecular weights between 500 and 3000 daltons (5). 

PROP status. Individuals classified as tasters of the bitter compound propylthiouracil (PROP) (not found in wine) have been reported to perceive bitterness more intensely and have a higher number of taste pores per taste bud and higher density of fungiform taste papillae on the tongue than non-tasters of PROP (32- 36). Despite this, PROP status has not been demonstrated to affect perception of bitterness or astringency of phenolic compounds in wine (73, 29) or water (75, 77, 79, 30). 

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