# Physicochemical and Microbiological Changes Associated with Processing in Dry-Cured Tuna
## 3 Results and Discussion
### Color Parameters  
Color is a basic sensory parameter in the evaluation of food quality because it is the first factor that triggers consumer perception of acceptability [45]. The lightness (L*), red and green scale (a*) and yellow and blue scale (b*) were measured in each processing step and the results are shown in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline  & **Raw Tuna** & **Salting** & **Salt-Washing** & **Dry-Cured Tuna** & \(p\)**-Value** \\ \hline L* & 33.98 \(\pm\) 3.70 b  & 40.75 \(\pm\) 5.24 a  & 41.74 \(\pm\) 4.61 a  & 29.94 \(\pm\) 2.64 b  & *** \\ a* & 4.12 \(\pm\) 1.30 a  & 1.39 \(\pm\) 1.47 b  & 0.23 \(\pm\) 2.02 c  & 2.31 \(\pm\) 1.06 b  & *** \\ b* & 7.87 \(\pm\) 1.29 b  & 9.91 \(\pm\) 1.25 a  & 9.00 \(\pm\) 3.00 ab  & 5.71 \(\pm\) 1.21 c  & *** \\ \hline C* & 11.98 \(\pm\) 2.24 a  & 10.16 \(\pm\) 1.23 ab  & 9.23 \(\pm\) 4.63 ab  & 8.02 \(\pm\) 1.30 b  & ** \\ h* & 59.82 \(\pm\) 5.03 b  & 81.79 \(\pm\) 8.65 a  & 91.37 \(\pm\) 14.48 a  & 67.53 \(\pm\) 9.96 b  & ** \\ \hline \end{tabular} Different letters in the same row indicate that there were significant differences. **, ***, ***-significant at \(p<0.001\), respectively.  
\end{table} 
Table 2: Changes in L*, a*, b*, C* and h* (mean \(\pm\) SD) parameters and function during the manufacturing process of _mojama_. Significant differences were found in the samples for the L* coordinate during the manufacturing process of _mojama_. The L* value was significantly affected by the salting process, with the flesh gaining a lighter color from 33.98 to 40.75 in the raw tuna and after the salting step samples, respectively. Hemoglobin and myoglobin are the basic pigments of the dark muscle of fish. NaCl is reported to enhance the removal of heme proteins such as hemoglobin (Hb) and myoglobin (Mb), resulting in a less pigmented color [46]. The salt-washing step increases the removal of heme proteins as well since they are water soluble, thus an increase in the L* value was noted (no significant) for the samples collected after this step. The tuna flesh samples obtained after the drying step were darker (29.94) because the drying step reduces the amount of free water on the surface, causing a decrease in the value of this coordinate [47]. The forced aeration during the drying step involved oxidation phenomena that could also contribute to that decrease. The red-green coordinate (a*) significantly decreased during the manufacturing process, with a later increase in the final product. Generally, the desired color in fresh fish is bright red, which is related to the content of Hb and Mb in the muscle [28]. As stated, the salting and salt-washing steps remove heme proteins so the a* values decreased significantly. Finally, the drying step could favor the development of oxidative phenomena, where the red color gradually becomes different shades of brown due to the conversion of oxymyoglobin to metmyoglobin (MMb) [48]. [PERSON] et al. [49] reported that the values of a* decrease when MMb content increases. During _mojama_ manufacturing, the b* coordinate (blue-yellow) of the samples analyzed increased after the salting and salt-washing steps, followed by a significant decrease for the samples obtained after the drying steps. Although this coordinate is the least studied color component in foods, particularly in fish products, it has been reported that it is influenced by the concentration of pigments and the state of the flesh (oxidized, reduced, or modified by chemical and/or biochemical reactions) as well as the structural changes that the muscle undergoes during the manufacturing process. Besides, an important characteristic to consider is that the yellow component of the color of tuna muscle decreases when it is subjected to the salting process [50] due to modifications/degradation of the carotenoids and the hemopigments occurring in the flesh [51]. Moreover, chroma (C*) and hue angle (h*) values were estimated using the L*, a* and b* parameters.