## 4 Discussion
### Physicochemical Characterization
#### 4.2.1 [PERSON] et al. [76] investigated the effect of supercooling conditions on the conservation of _Pyropia yezensis_. This was the only study encountered on the effect of storage conditions on the color of fresh \"layer\" seaweed. The main remarks were that \(L^{*}\), \(a^{*}\) and \(b^{*}\) values of the refrigerated fresh samples (stored at 5 \({}^{\circ}\)C) were affected by the storage temperature with the CIELAB values increasing more than that of the other samples stored at constant and step-cooling (\(-2\)\({}^{\circ}\)C) or frozen (\(-18\)\({}^{\circ}\)C), during the storage period of 15 days. This is not in accordance with our results in which there was a small decrease in \(a^{*}\) and no significant difference in \(b^{*}\) for PU-CTRL after 15 days of storage. It is possible that the differences between the results obtained by [PERSON] et al. and our results for PU-CTRL were due to the different experimental settings such as illumination [77; 78]. Because of the differences in how the MAP and VAC samples were treated, it is not reasonable to establish correlations between the studies.
Moreover, the available evidence suggests that an elevation in \(L^{*}\) values may occur due to pigment breakdown as a result of light oxidation, auto-oxidation (mainly, because of the presence of ROS), and even enzymatic reactions [26; 81; 82; 83]. The changes in the \(a^{*}\) and \(b^{*}\) coordinates for PU and UL were both affected by treatments and storage time. For PU, a small decrease was observed followed by an increase in \(a^{*}\) values, reflected in changes in red tones, for the MAP and VAC treatments, probably due to changes in phycobiliproteins, in particular phycoerythrins that have a reddish color [77; 78]. It should be noted that the increase observed from day 9 onwards seemed to be due to a red exudate (phycoerythrin release) observed mainly in PU-VAC, in a similar way to what was witnessed in the alga _Gracilaria salicornia_ (Rhodophyta) preserved under vacuum [35]. Chlorophylls appeared to play a minor role in changing \(a^{*}\) values for \"laver\" seaweeds as a result of their low concentration in these species [84]. With regard to \(b^{*}\), the significant decrease for both treatments (with more intensity for PU-VAC) seemed to occur due to alterations in the composition of carotenoids and phycocyanin-type phycbilins (of bluish coloration) [81; 85]. Phycocyanins were more stable than carotenoids, and the phycocyanin/carotenoids ratio appeared to increase with time, promoting a decrease in yellowish tones and an increase in bluish tones in red seaweeds [85]. For UL, all treatments implied an increase in \(a^{*}\) (less green intensity) over the storage time, which possibly occurs due to the degradation or adaptation of the chlorophylls to the experimental conditions [20; 32; 79]. Like PU, \(b^{*}\) values for UL also decreased with time, except for UL-MAP, which was not significantly different from day 0. These variations in \(b^{*}\) values may have been exclusively caused by changes in the carotenoid composition [20; 79]. Carotenoid content in seaweeds is directly affected by ROS through quenching activity, and indirectly by inducing the carotenoid biosynthetic pathway [86]. As both the VAC and MAP treatments involved the elimination of oxygen, it is possible that the absence of O\({}_{2}\), together with the presence of Ar and high CO\({}_{2}\) in the MAP samples, helped in the maintenance of carotenoids by suppressing oxidation reactions and/or enzymatic activities [86; 87]. A more yellowish coloration could be observed with the naked eye in samples processed by the MAP and VAC treatments on day 9 relative to CTRL (see Figure 9a). The adaptation or degradation of pigments due to light, extended duration and other storage conditions, together with metabolic responses to diverse sources of stress such as starvation (nutrient depletion) and cold damage, are the most possible hypotheses for the increasing \(L^{*}\) values and the changes observed in \(a^{*}\) and \(b^{*}\) for both PU and UL seaweeds [20; 32; 79; 88; 89; 90; 91]. It should also be taken into consideration that some of the variations observed throughout the storage days can arise from the heterogeneity of the samples, as can be observed in the different shades of green for UL and brown with discolored edges for PU, both presented in Figure 9b.