## 3 Results and Discussion  
### Effect of Thermal Processing on the Phytochemical Content of Broccoli Extracts  
Different thermal processing methods of broccoli heads resulted in significantly different phytochemical composition of the extracts (Table 1). The amount of total phenolic content was the highest in steamed and air-fried broccoli (0.72 \(\pm\) 0.12 mg GAE/g fw and 0.65 \(\pm\) 0.15 mg GAE/g fw, respectively), while boiled and blanched broccoli contained lower amounts (0.37 \(\pm\) 0.18 mg GAE/g fw and 0.47 \(\pm\) 0.21 mg GAE/g fw, respectively). This suggests that steamed and air-fried broccoli encapsulates these biochemicals more efficiently than boiled or blanched. A considerable amount of phenols was dissipated in water, as evidenced by the presence of phenols in the water remaining after boiling, blanching, and steaming. The same phenomenon was observed for all other polyphenic compounds (total flavonoids, hydroxcinnamic acids, tannins, and proanthocyanidins). All these phytochemicals exhibit limited (proanthocyanidins) [37] to moderate (polar aglycone flavonoids) water solubility [38], which is improved by heat [39]. Therefore, a considerable amount of these chemicals can be found in the hot water remaining after thermal processing. The fact that steaming does not include direct immersion of broccoli into the boiling water is the most likely reason why steamed broccoli has a higher total phenolic content than boiled or blanched. In addition, boiling and blanching are more \"aggressive\" methods, as more cells are damaged and the polysaccharide fibers are destroyed, which can lead to oxidation of the molecules [17; 40]. Similar results were found in Brussel sprouts and pumpkin [41], where a higher phenolic content was observed after air steam treatment, compared to water steaming. This could be due to the degradation that occurs in normal steaming treatment compared to the air steaming treatment due to the presence of air by oxidizing the antioxidant molecules [17]. In agreement with our results, [PERSON] and [PERSON] [13] showed that the total amount of phenolic compounds was also significantly lower in cooked and blanched white cauliflower compared to steamed and stir-fried. Flavonoids were also significantly reduced, with the greatest reduction occurring after boiling, followedby blanching, while stir-frying showed the best results [13]. Similar phenomenon was also recorded in air-fried eggplants with the highest polyphenolics content after air-frying [42]. In general, boiling and blanching are considered as very disruptive methods of vegetable thermal processing because phenolic compounds disintegrate during long heat exposure, and this was observed in green pea, pepper, beet and eggplant [43], as well as broccoli, cabbage, colored peppers, leek, peas, spinach, squash, and tomatoes [43; 44; 45; 46; 47]. The highest amount of phenolics retained by air-frying compared to other cooking methods was also noticed in red cabbage, green cabbage, broccoli sprouts, Brussel sprouts, and kale [14]. In some cases, certain thermogenic compounds such as canolol can even be formed during air-frying compared to other cooking methods [15; 16]. On the other hand, the water remaining after cooking (boiling) had significantly higher content of total flavonoids (2.72 \(\pm\) 0.59 mg QE/g fw) and proanthocyanidins (0.96 \(\pm\) 0.89 mg CatE/g fw) than all other samples. Among the tissues, air-fried and par-fried broccoli had the highest amount of preserved flavonoids (1.71 \(\pm\) 0.70 mg QE/g fw and 1.42 \(\pm\) 0.66 mg QE/g fw, respectively), while air-fried broccoli had the highest amount of preserved proanthocyanidins (0.42 \(\pm\) 0.13 mg CatE/g fw). Similar results were also recorded in broccoli florets [22], where the loss of flavonoids could be due to thermal degradation and \"leaching\" into cooking water. Steaming also proved to be a better cooking method than boiling and blanching in terms of preserving polyphenolics in green vegetables as well [48].