## 3 Results and Discussion
### Colour Characteristics and Opacity Parameter of Biopolymer Films  
Table 3 presents the colour characteristics and opacity of biopolymer films produced from ozone-treated FFSs. Ozone treatment significantly affected all colour parameters and the opacity of films (\(p<0.05\)). One of the most important factors in edible films developed for food products is colour [48].  
The \(L^{\star}\) values of the films ranged from 80.10 to 89.77; ozone treatment increased this value depending on the treatment time. The highest \(a^{\star}\) value was determined in the control film, and ozone treatment significantly decreased the \(a^{\star}\) value. However, similar \(a^{\star}\) values were obtained in the films from ozone-treated WPC (\(p\geq 0.05\)). On the contrary, ozone treatment increased the \(b^{\star}\) value of the films depending on the increasing treatment time. Hence, the films became slightly greenish (\(-a^{\star}\)), yellowish (\(+b^{\star}\)), and lighter (\(+L^{\star}\)) with the increased ozone treatment of the WPC. Similar to the present study, [PERSON] and [PERSON] [49] concluded that ozone treatment increased the lightness, yellowness, and greenness of the whey powder samples. This situation might be due to the carotenoid degradation in WPC depending on ozone treatment, which could cause a higher \(L^{\star}\) value and lower \(a^{\star}\) value in the samples [50]. Moreover, when milk-based products are utilised, the colour values are frequently impacted in this manner. A previous study reported that the colour differences in gelatine films with keifir addition were similar to the present study [51]. The colour difference (\(\Delta E^{\star}\)) indicates the degree of the total colour difference from the control sample. The ozone treatments of the FFSs increased the \(\Delta E^{\star}\) value compared to the control. The highest \(\Delta E^{\star}\) was determined in the O-30.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & **Thickness (mm)** & **Density (g/cm\({}^{3}\))** & \(\theta_{608}\) (\({}^{\circ}\)) \\ \hline Control & 0.31 \(\pm\) 0.01 ns & 1.13 \(\pm\) 0.04 a & 104.30 \(\pm\) 0.99 ns \\ O-5 & 0.30 \(\pm\) 0.02 & 1.00 \(\pm\) 0.02 b & 101.54 \(\pm\) 2.06 \\ O-10 & 0.34 \(\pm\) 0.01 & 1.04 \(\pm\) 0.02 ab & 101.10 \(\pm\) 1.56 \\ O-30 & 0.38 \(\pm\) 0.03 & 1.07 \(\pm\) 0.03 ab & 96.92 \(\pm\) 2.72 \\ \hline \end{tabular} Data are the mean \(\pm\) standard deviation (\(n=3\)). Different letters within the same column show the significant differences between the samples (\(p<0.05\)). Control: biopolymer film from non-ozonated FFS; O-5: biopolymer film from ozone-treated FFS for 5 min; O-10: biopolymer film from ozone-treated FFS for 10 min; O-30: biopolymer film from ozone-treated FFS for 30 min.  
\end{table}
Table 2: Thickness, density, and contact angle parameters of biopolymer films produced from the ozone-treated film-forming solutions (FFSs).  
The opacity of biopolymer films used in food packaging is crucial; films with higher opacity can restrict light transmission [52]. The opacity of film samples ranged from 0.107 to 1.120. The ozone treatment of the FFSs increased the opacity of the samples depending on the increasing treatment time. This could be attributed to the protein development in WPC by ozone treatment, which formed a denser network structure. Hence, the denser the cross-linking of disulphide bonds, the stronger the ability of the films to act as a barrier to UV light [53]. This was coherent with the higher opacity of gelatine film produced from ozone-treated FFSs containing WPC. A higher opacity of films depending on the ozone treatment could protect packaged foods from light. The exposure of foods to light can alter their sensory and nutritional properties due to photocatalytic reactions that produce activated free radicals [54]. Therefore, this situation was advantageous for food packaging.