# Effect of Chitosan on the Removal of Different Types of Tannins from Red Wines
## 1 Introduction  
Sustainability is progressively growing in importance in the wine industry [1, 2]. In recent years various industries in oenological products have increased production of new commercial, eco-friendly products, among these, one of the most interesting with characteristics of biocompatibility, biodegradability, and low toxicity is the chitosan C, admitted as a food additive from 2009, (EC) No 606/2009 [3]. Chitosan is a natural polysaccharide derived from chitin with polycationic character and a solubility variable in acidic media due to its deacetylation degree and molecular weight [4]. The use of C has been authorized in must and wine for microbial stabilization or metal and protein removal. The admitted range for the addition of chitosan is 10-500 g/hL according to the aim (Commission regulation (EU)) [5]. Previous studies reported several beneficial effects due to chitosan additions in wine, such as antimicrobial [6, 7] and antioxidant activity due to the direct radical scavenging mechanism [8] or indirectly, via metal chelation, which blocks the generation of radical species [9, 10, 11]. Chitosan is also of great relevance because it is effective in controlling \(B\). _bruxellensis_ during winemaking [12]. Given all these positive properties, C can be used on finished red wines to preserve them from microbial and oxidative spoilage. However, the possible effect on compoundsresponsible for wine sensory quality should also be considered. Recently, [PERSON] and colleagues [13] showed that a post-fermentative treatment with 0.5 g/L of C on a Sangiovese wine slightly affected aroma compounds and did not severely impair the quality parameters of the final wines. However, in this same work authors also observed that ellagic acid, a tannic molecule released in wines after contact with wood, was adsorbed onto chitosan and it reduced this content by 40%. In a previous study, we also detected a decrease in BSA reactive tannins after a treatment of an Aglianico wine with C [14]. Tannins are very important for red wine quality as they are responsible for their high dry extract and longevity but also for the sensory attributes linked to their ability to precipitate salivary proteins during tasting, causing an astringent sensation. This sensory attribute is typical of red wine but, if present at high intensity, it results in negative consumer reactions. Because most of premium red wines are rich in tannins and often are previously aged in barrels or in contact with tannins extracted from grapes and wood, it is interesting to determine if C could influence their content and reactivity towards proteins. During winemaking and storage, the addition of commercial tannins is definitively a practice often used to improve the wine quality. Tannins of grape origin, as well as of wood origin can be used [15]. Wood tannins are the hydrolysisable tannins, gallotannins, and ellagitannins, which are extracted from different botanical species [16]. Ellagitannins originate from oak and chestnut wood [17], while gallotannins mainly originate from galla and tara nuts [18]. Grape tannins are condensed flavanols mainly present in berry skins, seeds, and stalks [15]. One of the effects of the addition of tannins is the variation in the pigments and chromatic characteristics of wine, but important is also the effect on sensory attributes such as the astringency and astringency subqualities [19]. This is of particular importance especially considering that red wines rich in tannins change their chromatic characteristics and astringency during aging and exposition to controlled moderate amounts of oxygen [20; 21; 22]. Taking into consideration all these aspects, it is worth investigating the possible effect of C on tannins (condensed and hydrolysable) in addition to their reactivity towards salivary proteins, one of the mechanisms at the base of the sensation of astringency of red wines [23; 24].