# Effect of Chitosan on the Removal of Different Types of Tannins from Red Wines
## 3 Results and Discussion
### The Effect of Chitosan on Wines Rich in Tannins of Different Origin  
The effect of tannins addition and C on main phenolic parameters of wines is reported in Figure 1. As expected, the addition of tannins increased the concentration of total phenols and BSA reactive tannins compared with the control wine. The highest significant increase in total phenolics was detected only for GT. As the method we used to determine total phenols evaluated their reactivity towards iron [30], it is expected that gallotannins, molecules that form water-insoluble complexes with iron [35], gave a higher absorbance after the reaction of GT with the ferric chloride used in this assay. Similar results were showed by [36] in a study in which several enological tannins were assessed for their abilities to precipitate BSA protein and to react with ferric chloride. Figure 1: Fining effect on total phenols (**A**), tannins reactive to BSA (**B**), and vanillin reactive flavans (**C**). Different letters indicate a statistically significant difference among treated wines, according to [PERSON]’s (HSD) analysis (\(p<0.05\)). The effect of tannin addition is expressed with a capital letter on wines W, CT, ET, and GT (A, B, C), and the effect of chitosan addition is expressed with a lowercase letter on wines W-C, CT-C, ET-C, and GT-C (a, b, c). The asterisk (*) indicates a statistical difference between each kind of wine before and after the treatment with chitosan. All data are expressed as means \(\pm\) standard deviation. In agreement with a previous study [37], the CT sample showed the greatest increase in BSA reactive tannins compared with the treated wines. The increase is due to the molecular structure of condensed tannins which mainly are constituted of proanthocyanidins with a polymerization degree and composition in monomers highly reactive towards BSA [36]. No effect of enological tannins was detected for vanillin reactive flavans, VRF, probably because vanillin is mainly reactive towards low molecular weight proanthocyanidins [38]. Concerning the effect of C addition, a slight decrease in total phenols in W and ET (\(-15.68\%\) and \(-10.03\%\), respectively) was determined. According to [PERSON] et al. (2000) [39], C does not directly interact with phenolics and the decrease in phenolics compounds is more ascribable to a sedimentation effect [40]. In agreement with recent results [14], a decrease in BSA reactive tannins after the addition of C was detected for all wines. A slight VRF removal was instead detected only for W. In a previous study on white wines, [PERSON] et al. [41] detected a decrease in VRF after a treatment with C of a Sauvignon Blanc in which the levels of VRF were largely accountable for the presence of monomer catechins. In red wines, the amount of catechins is low compared with the structures with a higher polymerization degree and this could justify the absence of an effect of the treatment with C on the reactivity of wines towards vanillin, especially in wines treated with commercial tannins. A possible competition for the adsorption on C of different tann structures is not ruled out. If this is the case, the adsorption of phenolic structures highly reactive towards BSA is favoured. As reported in Table 1, after the addition of tannins, a decrease in individual anthocyanins analysed by HPLC was detected and the decrease was higher for ET. Simultaneously, the polymeric pigments increased in all experimental samples, probably due to the involvement of native anthocyanins in the formation of new pigments at higher polymerization degree, as already observed in previous experiments [42]. Concerning C, in agreement with literature [14; 43] the effect on pigments was limited but significant. The removal of total monomeric anthocyanins was significant for W and GT and those of polymeric pigments for ET and GT. However, the loss was never higher than \(7.40\%\).