## 3 Results and Discussion
### Effect of Chitosan on Color Features and Anthocyanins Composition of Wine  
CIELab parameters, co-pigmentation magnitude and anthocyanins content of samples were evaluated and presented in Tables 3 and 4. Both chitosan treatments (KT and KTS) reduced significantly the contribution of co-pigmentation and polymerization to the color of wines. Co-pigmentation is a phenomenon of reinforcement of wine color favored by the presence of \(\pi\) conjugated systems and hydrogen bond donor/acceptor groups of certain molecules (co-pigments) which leads to the formation of \(\pi\)-\(\pi\) stacking interactions with anthocyanins [29]. In red wines, the main compounds described as powerful copigments are (i) flavonoids such as quercetin or myricetin, due to the extended conjugation of the three constitutive aromatic rings and (ii) hydroxycinnamic acids, especially the ones closely linked to anthocyanins by acylation of glycosyl groups [29; 30]. Interestingly, as previously discussed, the content of these two families of compounds, were particularly reduced after chitosan treatments. \begin{table}
\begin{tabular}{c c c c} \hline  & **C** & **KT** & **KTS** \\ \hline \% Co-Pigmentation & 9.7 \(\pm\) 2.7 a & 0.0 \(\pm\) 0.1 c & 6.1 \(\pm\) 1.8 b \\ \% Anthocyanins & 36.5 \(\pm\) 2.1 b & 52.5 \(\pm\) 4.0 a & 46.9 \(\pm\) 2.1 a \\ \% Polymers & 53.8 \(\pm\) 0.7 a & 47.5 \(\pm\) 2.4 b & 47.0 \(\pm\) 0.8 b \\ _CIELab parameters_ & & & \\ L* & 19.43 \(\pm\) 2.62 b & 25.72 \(\pm\) 0.11 a & 24.1 \(\pm\) 0.51 a \\ a* & 48.17 \(\pm\) 3.28 b & 54.82 \(\pm\) 0.14 a & 52.8 \(\pm\) 0.43 a \\ b* & 34.98 \(\pm\) 4.03 b & 40.10 \(\pm\) 0.08 a & 37.9 \(\pm\) 0.55 a \\ C* & 57.83 \(\pm\) 4.97 b & 67.93 \(\pm\) 0.16 a & 65.0 \(\pm\) 0.67 a \\ h\({}_{\text{ab}}\) & 33.50 \(\pm\) 1.49 b & 36.19 \(\pm\) 0.05 a & 36.7 \(\pm\) 0.18 a \\ \hline \end{tabular}
\end{table} 
Table 3: Percentage contribution to the color and CIELab parameters of wines after 7 days of treatment with chitosan. In the same row, different letters indicate significant differences according to [PERSON]’s test (\(p<0.05\)). \(n=3\). C: no addition; KT: 0.5 g/L of solid chitosan; KTS: 0.5 g/L of chitosan in solution. Besides, a particular attention should be paid to ellagic acid since this compound, because of its extended planar conformation, has demonstrated to spontaneously binds to pigments by means of Van der Waals interactions, conferring to this molecule a high co-pigmentating potential [31; 32]. Thus, the reduced co-pigmentation levels in samples treated with chitosan could be due to a lesser content of available cofactors already adsorbed on chitosan, e.g., hydroxycinnamic acids, flavonoids and ellagic acid. In Table 3, a lower percentage of color due to polymers is also shown for chitosan samples. The reason to this evidence may be partially due to the reduction of vitisins or ethyl adducts which will be commented in the following section. Those compounds, in fact, being stable to SO\({}_{2}\) addition, are included into the polymeric fraction by the analytical method we used. CIELab parameters significantly changed after treatments with chitosan (Table 3) in accordance with what already found in a previous research [9]. As a general trend, co-pigmentation and self-association have been shown to produce a hyperchromic effect on red wines, leading them to darker colors (lower L*), and increased saturation (C*), also depending on the co-factor considered [33; 34; 35].