## 3 Results and Discussion
### Effect of Thermal Processing on the Phytochemical Content of Broccoli Extracts
In addition, the content of flavonoids in garden spinach leaf, Indian spinach leaf, and green leaf amaranth was higher after frying compared to boiling [49] which is due to a higher availability of the compounds trapped in fibers [50]. Additionally, higher levels of some proanthocyanidins were shown to protect the vegetable quality in deep frying oil by inhibiting oxidation [51], which would explain higher percentage of most phytochemicals in pan-fried broccoli. The total hydroxcinnamic acid content was highest in the water remaining after steaming broccoli (1.50 \(\pm\) 0.64 mg CAE/g fw) and in air-fried broccoli (1.58 \(\pm\) 0.71 mg CAE/g fw). Steamed broccoli tissue had the highest total tannin content (0.46 \(\pm\) 0.19 mg GAE/g fw). Although frying reduces the amount of phytochemicals compared to raw vegetables due to the high temperatures, it was shown that hydroxycinamic acids from fried red skin onion had a higher bioavailability after digestion compared to other types of baking and grilling [52], which indicates that frying had a less negative effect on these compounds. \begin{table}
\begin{tabular}{c c c c c} \hline  & **TP (mg GAE/g fw)** & **TF (mg QE/g fw)** & **THCA (mg CAE/g fw)** & **TPAN** \\ BOW & 0.37 \(\pm\) 0.18 bc & 0.54 \(\pm\) 0.13 c & 0.72 \(\pm\) 0.40 bc & 0.18 \(\pm\) 0.09 cd & 0.13 \(\pm\) 0.03 b \\ BOW & 0.39 \(\pm\) 0.20 bc & 2.72 \(\pm\) 0.59 a & 0.92 \(\pm\) 0.50 abc & 0.29 \(\pm\) 0.05 bc & 0.96 \(\pm\) 0.89 a \\ BL & 0.47 \(\pm\) 0.21 b & 0.86 \(\pm\) 0.25 c & 0.50 \(\pm\) 0.35 c & 0.22 \(\pm\) 0.10 bcd & 0.15 \(\pm\) 0.06 b \\ BLW & 0.25 \(\pm\) 0.16 c & 0.74 \(\pm\) 0.25 c & 0.64 \(\pm\) 0.38 bc & 0.10 \(\pm\) 0.08 d & 0.41 \(\pm\) 0.45 b \\ ST & 0.72 \(\pm\) 0.12 a & 1.49 \(\pm\) 0.47 b & 1.19 \(\pm\) 0.56 ab & 0.46 \(\pm\) 0.19 a & 0.31 \(\pm\) 0.04 b \\ STW & 0.43 \(\pm\) 0.34 bc & 0.75 \(\pm\) 0.25 c & 1.50 \(\pm\) 0.64 a & 0.27 \(\pm\) 0.23 bc & 0.07 \(\pm\) 0.05 b \\ AF & 0.65 \(\pm\) 0.15 a & 1.71 \(\pm\) 0.70 b & 1.58 \(\pm\) 0.71 a & 0.27 \(\pm\) 0.10 bc & 0.42 \(\pm\) 0.13 b \\ PF & 0.39 \(\pm\) 0.20 bc & 1.42 \(\pm\) 0.66 b & 0.98 \(\pm\) 0.37 abc & 0.35 \(\pm\) 0.15 ab & 0.21 \(\pm\) 0.06 b \\ \hline \end{tabular} Values represent average \(\pm\) standard deviation of three biological and four technical replicates. Different letters indicate a significant difference among the values in a row (one-way ANOVA, Duncan’s test, \(p\leq\) 0.05). fw = fresh weight; BO = broccoli boiled; BOW = water after boiling broccoli; BL = broccoli blanched; BLW = water after blanching broccoli; ST = broccoli steamed; STW = water after steaming broccoli; AF = broccoli air-fried; PF = broccoli blanched and then pan-fried; TP = total phenols; GAE = gallic acid equivalent; TF = total flavonoids; QE = quercetin equivalent; THCA = total hydroxcinnamic acids; CAE = caffe acid equivalent; TPAN = total proanthocyanidins; CatE = catechhin equivalent; TT = total tannins.  
\end{table} 
Table 1: Effect of different thermal processing techniques on different groups of polyphenolics in broccoli extracts. Unfortunately, no comparisons were found between fried and boiled/steamed/blanched onion to determine whether there are even greater losses of hydroxycinnamic acids when being cooked in other ways. Similarly, potatoes, still retain a high amount of hydroxycinnamic acids, despite the high temperatures reached during frying in oil, suggesting that frying does not necessarily have a negative impact on phytochemical integrity [53; 54]. Although most of the mentioned phytochemicals remain preserved in broccoli when air-fried or pan-fried, total tannin content was the highest in steamed broccoli (0.46 \(\pm\) 0.19 mg GAE/g fw), while in air-fried and pan-fried broccoli, their levels were lower (0.27 \(\pm\) 0.10 mg GAE/g fw and 0.35 \(\pm\) 0.15 mg GAE/g fw, respectively). The tannin composition of different vegetables varied depending on the type of thermal processing.