## 3 Results and Discussion
### Effect of Growing Medium on the Quality of Lettuce
#### 3.3.2 Effect of Growing Medium on the Leaf Antioxidant Compounds and Antioxidant Activity  
Statistical analysis performed by two-way ANOVA on the leaf antioxidant compounds and antioxidant activity at harvesting showed a significant effect of cultivar (C), growing medium (GM), and their interaction. The content of ascorbic acid was found higher in VDI than in the Imperiale variety (67.3 vs. 56.1 mg 100 g\({}^{-1}\) f.w.). The leaf content of this compound was affected by the interaction of the cultivar (C) with the growing medium (GM). The average values of total ascorbic acid found in this study were in the range of 53.6 to 71.8 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 39.2 to 86.5 mg 100 g\({}^{-1}\) f.w. In Figure 4, the effect of the cultivar (C) and growing medium (GM) interaction on the ascorbic acid at harvesting is represented. VDI showed the highest values in plants grown in the C2-60 and C3-30 substrates. No significant differences in the leaf ascorbic acid content were observed for cv IMP in dependence on the growing medium. The leaf ascorbic acid content resulted in a comparison between the two cultivars when grown on a control growing medium, TC. The observed increase in ascorbic acid agrees with previous results in which the ascorbic acid concentration was higher with compost in strawberries, peppers, and rocket salad [82], and in which a cultivar-specific response to lettuce in closed soilless cultivation was found [83]. Ascorbic acid is a potent biological antioxidant involved in both pathogen defense mechanisms and growth modulation via phytohormone signaling [36]. The observed increase in ascorbic acid could be related to the presence of compounds in the compost that  
Figure 4: Effect of the cultivar (C) and growing medium (GM) interaction (significant at \(p<0.01\)) on the leaf ascorbic acid 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 \(p\leq 0.05\). IMP: Imperiale lettuce cv; VDI: Verde d’Inverno lettuce cv; TC: Peat-based substrate; C1-60: 60% Composd 1 + 40% Peat; C1-30: 30% Composd 1 + 70% Peat; C2-60: 60% Composd 2 + 40% Peat; C2-30: 30% Composd 2 + 70% Peat; C3-30: 30% Composd 3 + 70% Peat; C3-60: 60% Composd 3 + 40% Peat. increase the antioxidant capacity of plants, as suggested by [PERSON] [84]. This beneficial effect is important both for the nutritional properties of the lettuce and for the marketing of the product. In fact, based on [PERSON] et al. [85], the shelf life of baby leaf lettuce is favored by high concentrations of ascorbic acid and tocopherols by safeguarding phenolic compounds. The polyphenols, flavonoids, and antioxidant activity were found higher in IMP than VDI cultivar (respectively, 488.6 vs. 435.9 mg GAE 100 g\({}^{-1}\) f.w., 292 vs. 274.1 CE mg 100 g\({}^{-1}\) f.w., and 2337.7 vs. 2016.1 umol TE 100 g\({}^{-1}\) f.w.). In the present work, the polyphenol content was in the range of 367.1 to 551.4 mg GAE 100 g\({}^{-1}\) f.w., resulting in slightly higher than the ones found by [PERSON] et al. [73] and [PERSON] et al. [47], taking into account that the average dry matter (d.w.) value found in our samples was 15%. Indeed, these authors reported an average value, respectively, of 2467.8 mg GAE 100 g\({}^{-1}\) d.w. and 18.43 mg GAE g\({}^{-1}\) d.w. According to [PERSON] et al. [34], several studies indicate that lettuce genotypes may have different polyphenol contents and levels of specific phenolic compounds, and they reported that in a study in which 25 lettuce cultivars were examined, the polyphenols ranged between 104 and 857 mg GAE per 100 g f.w. In Figure 5, the effect of the cultivar (C) and growing medium (GM) interaction on the polyphenols (a) and flavonoids (b) at harvesting is shown.