## 3 Results and Discussion
### Rheology of the Edible Coating Solution
#### 3.3.2 Dynamic Rheological Properties  
The study of dynamic viscoelastic properties of coating solutions led to obtain information about the molecular entanglement and molecular network formation during drying [59]. The LVR used in this study was the maximum stress value in the flat region of storage modulus (G') and stress curve. Stress value applied for Ch, Ch + LE-1 and Ch + LE-5 was of 0.1 Pa.  
Figure 3b shows the frequency dependence of the storage (G') and loss modules (G') of the different edible coating solutions studied, from 0.01 to 100 rad\(\cdot\)s\({}^{-1}\). According to mechanical spectra (Figure 3b), increased G' and G'' values were observed with the increase of angular frequency (\(\omega\)), with G'' exhibiting a larger increase for all the samples in comparison with G'. Higher G'' values were obtained for chitosan-licorice solutions, indicating that these solutions will behave as liquids during the mixer process for lower processing times. Then, to deform the material, the supplied energy would be lower in the case of the chitosan-licorice coatings [60].  
Furthermore, G'' > G'' for the pure chitosan coating solution in the entire frequency range applied, without any crossover point observed, exhibited the typical behavior of liquid-like solutions [61]. But, in the case of chitosan-licorice solutions, crossover points were reached, indicating a longest time required for chain disengagement of the polymer structures in the solution [62; 63]. This observed frequency dependence of G' and G'' indicates that chitosan-licorice solutions are a useful class of materials to be applied as films in food coating, since they can enhance adhesiveness and the hardness of the coating solution.  
Figure 3c shows the effect of temperature on G' and G'' values of the edible chitosan and chitosan-licorice coating solutions for a heating rate of 5 \({}^{\circ}\)C/min in the LVR and 0.1 Hz frequency. The effect of temperature on the variation of G' and G'' of the coating solutions exposes the phase transitions and elasticity and allows the selection of appropriate temperature ranges for the formulation and the application of the coating solution on the product.  
For all coatings, G'' was higher than G' in the whole range of temperatures studied, denoting the liquid-like behavior. Chitosan coating solution presents higher G' values than samples with 1% and 5% of LE, the ones which present similar values. Gelatinization does not occur because the high temperatures accelerate the mobility of chitosan molecules in the solution and reduce the intermolecular hydrogen bonding interactions, removing energized water molecules surrounding the chitosan chains [64].  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Treatment** & **K (Pa\(\cdot\)s\({}^{\mathbf{n}}\))** & \(n\) & **R\({}^{2}\)** & \(\sigma\left(\dot{y}\)=10 \(s^{-1}\right)\) (Pa)** \\ \hline Ch & 0.469 \(\pm\) 0.015 & 0.795 \(\pm\) 0.005 & 0.998 & 0.2 \\ Ch + LE-1 & 3.72 \(\times\) 10\({}^{-4}\)\(\pm\) 0.001 & 1.436 \(\pm\) 0.018 & 0.994 & 0.0047 \\ Ch + LE-5 & 1.76 \(\times\) 10\({}^{-4}\)\(\pm\) 0.001 & 1.503 \(\pm\) 0.012 & 0.998 & 0.0021 \\ \hline \end{tabular}
\end{table}
Table 4: Power Law parameters obtained for the edible coating solutions. Ch = Chitosan; Ch + LE-1 = Chitosan + 1% of licorice extract; Ch + LE-5 = Chitosan + 5% of licorice extract.