## 3 Results and Discussion
### Effect of Growing Medium on the Quality of Lettuce  
#### 3.3.1 Effect of Growing Medium on Content of Chlorophylls and Carotenoids  
Statistical analysis was performed by two-way ANOVA on leaf chlorophyll a, chlorophyll b, and total chlorophyll. The ratio of chlorophyll a/b and carotenoids at harvesting showed a significant effect of cultivar (C), while no significant effect of growing medium (GM) was observed. Cultivar (C) and growing medium (GM) interaction influenced only chlorophyll b and the ratio chlorophyll a/b. As for the effect of cultivar, chlorophyll a, total chlorophyll, and carotenoids were higher in the YDI than IMP variety, as shown in Table 8. The chlorophyll b content also resulted higher in YDI lettuce than in IMP (26.2 vs. 12.0 mg 100 g\({}^{-1}\) f.w. ), while the chlorophyll a/b ratio was lower (2.2 vs. 3.3 mg 100 g\({}^{-1}\) f.w.). The average values of total chlorophyll found in this study were in the range of 51.4 to 86.1 mg 100 g\({}^{-1}\) f.w. These data are in agreement with the results of [PERSON] et al. [47], who reported in 11 baby leaf lettuce varieties mean values from 33.9 to 60.6 mg 100 g\({}^{-1}\) f.w. Similar results were found by [PERSON] et al. [77] and [PERSON] et al. [78], who found in baby leaf lettuce an average chlorophyll content, respectively, of 49 and 50.8 mg 100 g\({}^{-1}\) f.w. As for carotenoids, [PERSON] [47], reported in 11 baby leaf lettuce varieties, an average carotenoid content of 36.76 ug g\({}^{-1}\) f.w. in the range from 1.85 to 126.98 ug g\({}^{-1}\) f.w. The differences found in chlorophyll and carotenoid content in lettuce cultivars are likely related to the structure of the head, which differs between IMP, butterhead type (closed head), and VDI, romaine type (open head). It has been reported that the different morphology of lettuce heads influences some nutritional and bioactive compounds; lettuce morphotypes with open heads have a greater surface area exposed to light that promotes photosynthetic activity and thus the synthesis of sugars, chlorophylls, and other relevant compounds, while cultivars with closed heads have a smaller surface area leading to lower content of metabolites [79]. [PERSON] and [PERSON] [80] also report variations in carotenoid content depending on head morphology in lettuce cultivars. In Figure 3, the effect of the cultivar (C) and growing medium (GM) interaction on chlorophyll b and the ratio of chlorophyll a/b at harvesting is shown. In the leaves of VDI grown on C1-60 and C2-60, chlorophyll b content was higher than those grown on TC while for Imperiale lettuce, chlorophyll b leaf content was not affected by growth medium. Significant differences in the leaf chlorophyll a/b ratio were observed for cv VDI that showed the highest values of the ratio when grown on control (TC). The chlorophyll a/b ratio of the leaves of the two lettuce varieties grown on TC was comparable; however, unlike VDI, no significant differences in the leaf chlorophyll a/b ratio were observed for cv Imperiale in dependence on the growing medium. Chlorophyll and carotenoids are both chromophores involved in photosynthesis. Chlorophyll a is an essential photosynthetic pigment present in the photosynthetic reaction centers. Generally, the ratio of chlorophyll a to chlorophyll b is one to three. Carotenoids are plant pigments involved in the photoprotection of chlorophylls. The health status of plants  
Figure 3: Effect of the cultivar (C) and growing medium (GM) interaction on the leaf chlorophyll b (significant at \(p<0.05\)) (**a**), and the ratio chlorophyll a/b (significant at \(p<0.001\)) (**b**) at harvesting. Vertical bars represent the standard deviation of mean values. Different letters mean that the values are significantly different according to [PERSON]’s test at \(p\leq 0.05\).