## 2 Results
### The Optimum Conditions for the Wet Ozonation  
Tuna peptide powder was treated by wet ozonation in 17 single-factor experiments, and the sensory evaluation results (fishy odor/taste) are shown in Table 2. When the ozone concentration was gradually increased from 0.1 mg/L to 104.6 mg/L with the  
\begin{table}
\begin{tabular}{c c c c} \hline
**Experiment** & **Time (min)** & **Ozone Concentration (mg/L)** & **Sensory Score** \\ \hline \multicolumn{4}{c}{Sensory scores for samples in single-factor dry ozonation experiments} \\ \hline  
b  \\ \hline \end{tabular}
\end{table}
Table 1: Sensory scores for samples in dry ozonation experiments (measured average value \(\pm\) standard error, \(n=3\)).  
same reaction time and temperature, the sensory scores ranged significantly from 2.2 to 5.0 (_p_ < 0.05). The results obtained in the single-factor experiments were used to design 25 orthogonal experiments of wet ozonation. In orthogonal wet ozonation experiments, the sample with an ozone concentration of 50.2 mg/L had a sensory score of 4.7 \(\pm\) 0.2, which was significantly higher than 2.3 \(\pm\) 0.2 (_p_ < 0.05). The optimal conditions for the wet ozonation of tuna peptide powder were identified as an ozone concentration of 99.1 mg/L, a treatment duration of 40 min, and a temperature of 50 \({}^{\circ}\)C (Table 2).  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Experiment** & **Time (min)** & **Temperature (\({}^{\circ}\)C)** & **Ozone Concentration (mg/L)** & **Sensory Score** \\ \hline \multicolumn{5}{c}{Sensory scores for samples in the single-factor wet ozonation experiments} \\ \hline  
\hline \end{tabular}
\end{table}
Table 2: Sensory scores for samples in the wet ozonation experiments (measured average value \(\pm\) standard error, \(n\) = 3).  
The sensory score first decreased and then increased with increasing ozone concentration (Figure 1a). When the ozone gas concentration was increased (the intake flow rate remained unchanged), the concentration of ozone dissolved in the peptide powder solution after a short period increased, thereby increasing the mass transfer efficiency. The sensory score was the lowest (2.2) at an ozone concentration of 99.1 mg/L and then increased again upon further increasing the ozone concentration. The peptide powder solution had reached saturation at an ozone concentration of 99.1 mg/L. When the ozone concentration increased beyond 99.1 mg/L, excess ozone would introduce other odors, reducing the deodorizing effect.  
The sensory score changed only slightly with increasing reaction time, producing a curve that approximates a straight line (Figure 1b). The sensory score changed only slightly with increasing reaction temperature, also producing a curve that approximates a straight line (Figure 1c). Although the increase in the temperature of the peptide powder solution increased the activity of organic molecules, it also decreased the solubility of ozone and thereby reduced the mass transfer efficiency. As a result, the impact of increasing temperature on the deodorizing effect was reduced. Therefore, the reaction temperature also had only a small effect on the deodorizing effect of wet ozonation.  
The data presented in Table 2 and Figure 1 show that, of the three variables, ozone concentration has the greatest impact on the deodorizing effect of wet ozonation of tuna peptide powder, with reaction temperature and reaction time having only a small impact. The optimal conditions for treating tuna peptides by wet ozonation were as follows: ozone concentration, 99.1 mg/L; reaction time, 40 min; and reaction temperature, 50 \({}^{\circ}\)C.