Properties of Wine Polysaccharides

*Leticia Martínez-Lapuente, Zenaida Guadalupe and Belén Ayestarán*

### **Abstract**

Polysaccharides are the main macromolecules of colloidal nature in wines, and play a fundamental role in the technological properties and organoleptic characteristics of the wines. The role of the different wine polysaccharides will depend on their quantity but also on their chemical composition, molecular structure and origin. Wine polysaccharides originate from grapes and yeast acting during the winemaking. The main polysaccharides present in wines can be grouped into three major families: (i) polysaccharides rich in arabinose and galactose (PRAG), (ii) polysaccharides rich in rhamnogalacturonans (RG-I and RG-II), which both come from the pectocellulosic cell walls of grape berries, and (iii) mannoproteins (MP) released by yeasts. This paper describes the origin, structure and role of the different wine polysaccharide families through a bibliographic revision of their origin and extraction into the wines, as well as their technological and sensory properties.

**Keywords:** wine, rhamnogalacturonans, polysaccharides rich in arabinose and galactose, rhamnogalacturonans, mannoproteins, technological and sensory properties

### **1. Introduction**

Polysaccharides are the main macromolecules of colloidal nature in wines. Therefore, these compounds play a fundamental role in the technological properties and organoleptic characteristics of the wines.

The content of the different polysaccharide families in the wines depends mainly on the grape variety and its degree of maturation, the winemaking technology used (including type of strain of yeast and bacteria), and the transformation of the polysaccharides during the wine aging process [1–5]. These macromolecules show different technological properties in wines. Wine polysaccharides are widely known for their effect on the physicochemical stabilization of wine; thus, they are able to interact with the colloidal particles present in wines, reducing their reactivity and limiting their aggregation and flocculation [6]. These macromolecules have the ability to interact and aggregate with tannins [7], prevent the formation of protein haze in white wines [8], and delay or even arrest the outgrowth of the crystals of potassium bitartrate to a macroscopic visual size [9]. Wine polysaccharides have also been associated to the mouthfeel perceptions because they are able to modify the sensory properties of wines [7, 10]. Several authors [10, 11] have observed that wine

polysaccharides can modulate the astringency perception, increasing the sweetness sensation and body. Astringency is usually defined as the array of tactile sensations felt in the mouth including shrinking, puckering and tightening of the oral surface. In addition, polysaccharides are able to interact with wine volatile compounds [12], and thus affect the aroma of the wines.

Polysaccharides are extracted during the mechanical operations applied to the grapes (destemming-crushing, pressing and pumping of the crushed destemmed grapes) and during some stages of the winemaking. Therefore, polysaccharides are released in white, rosé and red winemaking during the premaceration process before starting the alcoholic fermentation, but also during the maceration fermentation of the red wine elaborations, and during the aging of the wines on their lees. On the contrary, other stages of the winemaking, such as filtration, produce a decrease in the content of wine polysaccharides [5].

Wine polysaccharides come from both the cell walls of the grape itself, and the yeasts and other microorganisms that act during the winemaking process. **Figure 1** shows a classification of the polysaccharides present in wines according to their origin.

From an oenological point of view, polysaccharides from grapes and yeasts are the most important both quantitatively and qualitatively. Therefore, the main polysaccharides present in wines can be grouped into three major families: (i) polysaccharides rich in arabinose and galactose (PRAG) [13] and (ii) polysaccharides rich in rhamnogalacturonans (RG-I and RG-II), which both come from the pectocellulosic cell walls of the grape berries [13], and (iii) mannoproteins (MP) produced and released by yeasts during the fermentation and the aging of wines on their lees [8]. Other wine polysaccharides such as glucans, produced by *Botrytis cinerea*, only become relevant when an infection with this fungus occurs, causing difficult clarifications and filtrations. Bacterial polysaccharides are present in the wines in very low concentrations. Polysaccharides exogenous to wine include carboxymethylcellulose and arabic gum, which are additives allowed by the International Organization of Vine and Wine (OIV).

Among all these types of polysaccharides, not all show the same behavior with respect to wines, and their concrete effects and properties will depend on their size, chemical composition, molecular structure and origin.

The objective of the present paper is to describe the origin, structure and key role of the different wine polysaccharide families through a bibliographic revision of their origin and extraction into the wines, as well as their technological and sensory properties.

**127**

**Figure 2.**

*Different layers of the grape skin.*

*Properties of Wine Polysaccharides*

plant cell wall [19].

*DOI: http://dx.doi.org/10.5772/intechopen.85629*

**2. Grape polysaccharides: origin, structure and functions**

The plant cell wall is composed of a highly integrated and structurally complex

Grape berries are composed of three main tissue types [20]: the skins, the pulp and the seeds. The structural properties of the cell walls of grape berries, especially the cell walls from the exocarp (the skin), determine the mechanical resistance, the texture, and the ease of processing berries. Grape skins represent about 5–10% of the total dry weight of the grape berry, and act as a hydrophobic barrier to protect the grapes from physical and climatic injuries, dehydration, fungal infection and UV light. The grape skin itself can be divided into three superimposed layers (**Figure 2**) [21]: (1) the outermost layer, the cuticle, is composed of hydroxylated fatty acids called cutin, and is covered by hydrophobic waxes; (2) the intermediate epidermis, assumed to consist of one or two layers, which appears as a regular tilling of cells; and (3) the inner layer, the hypodermis, which is the layer closest to the pulp, and which is composed of several cell layers that contain most of the phenolics

network of polysaccharides, including celluloses, hemicelluloses and pectins, and also structural proteins [14]. Pectins are a family of heteropolysaccharides characterized by a high content of α-D-galacturonic acid residues partially methyl esterified [15]. These heteropolysaccharides are located in the middle lamella of the primary cell walls, and are mainly composed of a galacturonic acid backbone and chains of several monosaccharides. The smooth region is represented by homogalacturonans (HG), which are galacturonic acid chains more or less methylated/ acetylated; the hairy region (high density of side chains) is composed of rhamnogalacturonans type I (RG-I) and type II (RG-II) [16]. RG-I consists of rhamnose and galacturonic acid and represents a very small proportion of grape-based pectins; RG-II is formed in the grape berry during the maturation and is released into the wine during the winemaking. Arabinogalactan proteins (AGP) are glycoproteins also located in the plant cell walls and extracted during the winemaking. They are themselves sidechains of the backbone that arise from the hairy region of pectins and are connected via specific hydroxyproline-rich proteins and, together with arabinogalactans, contribute to the so-called *polysaccharides rich in arabinose and galactose* (PRAG) [17]. Hemicellulose is formed by several polymeric structures in which xyloglucan (a backbone of cellulose with side chains containing xylose, galactose and fucose) is the most abundant [18]. Cellulose microfibrils represent the major constituent of the cell wall polysaccharides, and they are interacting with hemicellulose and pectic polysaccharides, improving the structural integrity of the

#### **Figure 1.**

*Classification of the main polysaccharides of wines according to their origin.*

*Pectins - Extraction, Purification, Characterization and Applications*

and thus affect the aroma of the wines.

decrease in the content of wine polysaccharides [5].

International Organization of Vine and Wine (OIV).

chemical composition, molecular structure and origin.

*Classification of the main polysaccharides of wines according to their origin.*

polysaccharides can modulate the astringency perception, increasing the sweetness sensation and body. Astringency is usually defined as the array of tactile sensations felt in the mouth including shrinking, puckering and tightening of the oral surface. In addition, polysaccharides are able to interact with wine volatile compounds [12],

Polysaccharides are extracted during the mechanical operations applied to the grapes (destemming-crushing, pressing and pumping of the crushed destemmed grapes) and during some stages of the winemaking. Therefore, polysaccharides are released in white, rosé and red winemaking during the premaceration process before starting the alcoholic fermentation, but also during the maceration fermentation of the red wine elaborations, and during the aging of the wines on their lees. On the contrary, other stages of the winemaking, such as filtration, produce a

Wine polysaccharides come from both the cell walls of the grape itself, and the yeasts and other microorganisms that act during the winemaking process. **Figure 1** shows a classification of the polysaccharides present in wines according to their origin. From an oenological point of view, polysaccharides from grapes and yeasts are the most important both quantitatively and qualitatively. Therefore, the main polysaccharides present in wines can be grouped into three major families: (i) polysaccharides rich in arabinose and galactose (PRAG) [13] and (ii) polysaccharides rich in rhamnogalacturonans (RG-I and RG-II), which both come from the pectocellulosic cell walls of the grape berries [13], and (iii) mannoproteins (MP) produced and released by yeasts during the fermentation and the aging of wines on their lees [8]. Other wine polysaccharides such as glucans, produced by *Botrytis cinerea*, only become relevant when an infection with this fungus occurs, causing difficult clarifications and filtrations. Bacterial polysaccharides are present in the wines in very low concentrations. Polysaccharides exogenous to wine include carboxymethylcellulose and arabic gum, which are additives allowed by the

Among all these types of polysaccharides, not all show the same behavior with respect to wines, and their concrete effects and properties will depend on their size,

The objective of the present paper is to describe the origin, structure and key role of the different wine polysaccharide families through a bibliographic revision of their origin and extraction into the wines, as well as their technological and

**126**

**Figure 1.**

sensory properties.
