## 3 Results and Discussion
In contrast, phenolic acids represented 97% of the total bound phenols (BPs), with the remaining 3% attributed to flavonoids. For the raw material S+SP, the predominant free phenol was the flavonoid patuletin-3-glucosyl-(1-6)-[2 pyosyl(1-2)]-glucoside, with a concentration of 85.1 mg/kg dw. In order of concentration, other flavonoids followed such as spinacetin glucuronide (61.6 mg/kg dw), patuletin-diglucoside (53.8 mg/kg dw), and patuletin-derivative (51.9 mg/kg dw). These findings are in accordance with previous studies on the phenolic composition of spinach leaves by LC-MS [42; 43]. In the bound phenolic fraction, ferulic acid, \(p\)-coumaric acid, and diferulic acid were detected as the most abundant at concentrations of 173.4, 79.9, and 39.5 mg/kg dw, respectively. These high phenolic acid contents in spinach have already been reported by other authors [44; 45]. The total concentration of FPs and BPs in the S+SP raw material reached values of 496.9 and 322.6 mg/kg dw, respectively, for a total amount of 819.6 mg/kg dw. As already seen for the tomato powder-enriched pasta, the process significantly affected (\(p<0.05\)) the total phenolic content of the uncooked spinach powder-enriched pasta (P-SS). In particular, 65.6% of the free phenols and 54.7% of the bound phenols were lost during processing, bringing the total phenolic content to 171.1 mg/kg dw and 146 mg/kg dw, respectively. Most of the flavonoids detected in the raw material were no longer present in the uncooked pasta sample or were present but with significantly lower contents. Nonetheless, patuletin-3-glucosyl-(1-6)-[2 pyosyl](1-2)-glucose was still the most abundant free phenol, together with spinacetin glucuronide and patuletin-diglucoside (46.6, 10.9 and 18.6 mg/kg dw, respectively). The patuletin derivative was the only compound that did not show a significant (\(p<0.05\)) difference from the level found in the raw material. With respect to BPs, ferulic acid, \(p\)-coumaric acid, and diferulic acid were still the principal phenols but with a significant (\(p<0.05\)) decrease in their concentrations compared to the raw material (82.6, 17.6, and 31.3 mg/kg dw, respectively). The cooking process led to a further significant degradation in phenolic compounds in the P-SS sample. The concentration of free phenols dropped by 88%, reducing the total amount to just 20.5 mg/kg dw. This decrease is mainly due to the significant drop in concentration of the main flavonoids, as partly already observed for the cooked pasta enriched with tomato powder. Flavonols are especially vulnerable to heat and undergo degradation when cooking pasta. [PERSON] and co-workers [46] explored the thermal stability of various flavonoids, finding that flavonoids, such as ruin, undergo strong degradation when exposed to temperatures above 100 \({}^{\circ}\)C. This degradation is attributed to the specific chemical structure of flavonoids, which makes them more easily degraded at high temperatures. Furthermore, [PERSON] et al. [26] found the same trend in wholemeal buckwheat pasta, where all the flavonoids were lost during the cooking process. All these results confirm the high thermo instability of this class of phenols, independently of the origin matrix. On the other hand, the BP fraction exhibited a smaller decrease, with a total phenol content not significantly (\(p<0.05\)) different compared to the uncooked pasta sample. The few flavonoids present were all lost after cooking, while the two main phenolic acids (ferulic and diferulic acid) did not show large significant differences from the uncooked pasta. Other previous studies found this behaviour for phenolic acids in high-temperature water [47].